Preparation of Reagent for Immune Complex Isolation

This invention relates to immune complex isolation.

It is known to isolate circulating immune complexes from sera by contacting the sera with a component that binds to the immune complexes and may be removed with them. It has been proposed to isolate the circulating immune complexes for use in diagnosing diseases or detecting auto-immune disorders or for research purposes by correlating the appearance of certain circulating immune complexes and their levels with diseases or with other factors to be detected or identified.

In one prior art technique, immunoglobulin complexes are precipitated with polyethylene glycol. This technique has a disadvantage in that, under many circumstances, the amount of monomeric immunoglobulin precipitated is so large that determinations based on total precipitation of monomeric immunoglobulin and immune complexes are difficult because changes in the amount precipitated are not sufficiently representative of the immune complexes present in the subject. Moreover, if the sample is plasma rather than serum, other precipitates further complicate the analysis.

In another prior art technique for isolating circulating immune complexes, the circulating immune complex is bound to bovine conglutenin through fixed C3 complement components. In still another technique, the circulating immune complex is bound to human Clq which has been immobilized in an affinity chromatographic column and then eluted with a diaminoalkyl compound.

These prior art techniques have several disadvantages such as: (1) they do not isolate a sufficient quantity of curculating immune comples to enable an analysis of the antigen moiety; (2) they are not sufficiently specific; and (3) they are relatively expensive and difficult to use because they require specialized equipment.

Accordingly, it is an object of this invention to provide a novel reagent for precipitating immune complexes;

It is a further object of this invention to provide a novel technique for isolating circulating immune complexes from serum or plasma;

It is a still further object of the invention to provide a novel technique for diagnosing diseases;

It is a still further object of this invention to provide a novel method of screening sera to detect the presence of abnormalities;

It is a still further object of this invention to provide a novel method for separating immune complexes from monomeric immunoglobulin and other materials in sera;

It is a still further object of this invention to provide a novel technique for precipitating immune complexes without specialized equipment;

It is a still further object of the invention to provide a technique for detecting autoimmune disorders.

It is a still further object of the invention to provide a novel immunotherapy technique.

It is a still further object of the invention to provide a novel kit for detecting circulating immune complexes.

In accordance with the above and further objects of the invention, a reagent which is a derivative of animal sera, is obtained, having the ability to bind complex immunoglobulin without binding to monomeric immunoglobulin. It may be used to screen for abnormalities by isolating immune complexes without substantial monomeric immunoglobulin. The reagent and circulating immune complexes bound to it are efficiently separated from other materials in sera or plasma. The immune complexes and reagent may be seaprated from each other after being removed from sera or plasma and relatively pure antigen obtained. The combined reagent and circulating immune complexes may be separated by precipitation or by attachment of the circulating immune complexes to reagent that has been immobilized on a solid surface.

The reagent, RhC, coprecipitates the immune complexes from the blood serum when: (1) incubated with animal blood serum or plasma; and (2) precipitated by dialysizing against a high pH buffer. In the alternative, RhC may be immobilized on a solid surface and animal blood serum or plasma brought itno intimate contact with it. The existence of disease is indicated by the amount of immune complex isolated and specific diseases may be diagnosed by conventional analysis of the precipitate or immune complex attached to the immobilized reagent. The reagent is isolated from the animal sera by changing the ionic strength of the serum and adjusting the pH to a value between 5.0 and 6.5 In the preferred embodiment, the ionic strength and ionic content is changed by dilution to facilitate the formation of the reagent.

The reagent includes at least two components; which are believed to attach to different regions of the Fc of the antibodies only when the antibodies have combined with antigen. The reagent can be caused to separate from sera after the reagent has bound to immune complexes, usually by precipitation or affinity chromotography, under conditions that do not cause the monomeric immunoglobulin to separate with it. The one factor is believed to be a rheumatoid factor or a portion of a rheumatoid factor and the other factor is believed to be a complement component or a portion of a complement component and they are believed to bind to portions of the Fc region of different antibody complexes.

One of the components of the reagent is IgG and in the preferred embodiment this component is equine IgG and is the major protein content of the reagent. At least one other component of the reagent is anodic and combined with the cathodic Ig. This other component or components appears to be a component of horse serum because of its origin and because it reacts with antinormal horse serum, which can detect its presence.

Together these two components selectively isolate a much larger portion of the immune complex than of monomeric immunoglobulin. Under some circumstances, both broader spectrum of the immune complexes and a larger amount of each type of immune complex is isolated. It is believed that IgM and all subclasses of IgG are isolated. The reagent may be packaged for every application to assay samples.

In use, the reagent and a human or other animal sample is mixed, the immune complexes bind to the reagent and the combination is separated from characteristics of the reagent or combination of reagent and immune complex that differ from the characteristics of monomeric immunoglobulin under some circumstances. The immune complexes are then analyzed.

To isolate the immune complex in one embodiment, the reagent and sample are mixed and: (1) the ionic strength of the mixture is changed; and (2) the pH is adJusted to between pH 6.5 and pH 9.5. The ionic strength is adjusted by adjusting the salt concentration to 0.05M in the pH range of 6.5 to 9.5 The immune complex precipitates and the precipitate is subject to separation of reagent and complex. In another embodiment, the reagent is immobilized on a solid surface and brought into contact with the sample. The immune complex binds to the immobilized reagent and is separated from the complex with the solid support. The complexes may be correlated with known complexes to identify then, or the antibodies may be separated from the antigen and the separate antigen or antibodies used for identification or immunotherapy. An antibody may be developed and used subsequently to identify the antigen or modified antibodies may be formed and used for immunotherapy. Antibodies may also be used to locate specific antigens in the subject.

From the above description, it can be understood that the technique and reagen of this invention has several advantages such as: (1) the reagent is inexpensive and easy to use to quantitate immune complexes; (2) the technique enables a simple and inexpensive diagnosfic possibility for diseases; (3) the reagent may be sold separately to laboratories who may perform the diagnosis at their laboratories without the use of expensive equipment; (4) the technique is specific and accurate in quantitative determination of immune complexes; (5) the reagent precipitates or otherwise isolates sufficient quantities of immune complex for analysis: (6) the technique permits a relatively simple quantitative isolation of immune complexes from serum or plasma; and (7) the technique produces better results at a lower cost.

Broadly, a protein complex is provided including at least portions of a rheumatoid-like factor and a complement-like component. This protein complex is formed as a result of the chemical manipulations of animal serum and has the characteristics of attaching to immune complexes but not monomeric immunoglobulin.

At least 25 micrograms (ug) of reagent protein is used to assay one sample and each sample that is assayed has at least the immune complexes of twenty-five microliters (ul) of undiluted animal serum. For screening in diagnosis, less than 600 ug of reagent must be used for the equivalent 100 ul of serum or plasma to be able to effectively distinguish normal from diseased subjects. The words "equivalent serum" or "equilent plasma" are used to take into account the common use of dilution or concentration of the sera or plasma. For example, the use of a fraction of a diluted sample such as one-third of a sample diluted by two volumes of diluent, each volume of which is equal to the one-third volume of the sample may be reacted with one-third as much reagent. The dilution aids in obtaining a more accurate value in cases where there are substantial amounts of immune complex. For separating the antigen when screening is not a concern, less than 2000 ug of reagent must be used for the equivalent immunoglobulin of 100 ul of serum or plasma to be able to effectively separate antigens.

A reagent including this protein complex may be frozen or powdered and packaged for application or immobilized on a solid surface. In one embodiment of assay requiring bulk mixing of the reagent with the sample, two and one-half milligrams of protein for each milliliter of solution is used to assay one human sample.

The reagent is isolated from animal sera drawing off the sera and precipitating a powder containing the reagent. Precipitation is caused by removing salts from the sera and adjusting the pH to a value between 5.0 and 6.5 The precipitate is purified prior to use by removing a large amount of the lipids from it.

This soluable protein complex precipitates when dialyzed against a high pH buffer and surprisingly, if it is incubated with serum or plasma containing immune complexes, it coprecipitates them at a pH in the range of 6.5 to 9.5 under low ionic strength conditions. Various immunological assays can then determine what kinds and how much immune complexes were in the original materia. The complexes may be used to diagnose certain disorders of the autoimmune system and certain diseases.

In this specification serum is considered the clear liquid which separates in the clotting of blood from the clot and the corpuscles and is thus a constituent of blood. Plasma is considered the fluid portion of the blood in which the corpuscles are suspended.

The amount of precipitate of immune complexes is consistent for a sample amount of reagent and conditions of precipitation and thus can be used to screen for abnormalities in the animal from which the serum was extracted. It is not known if all of the immune complexes are isolated, but the amounts are sufficiently consistent to provide positive indications of disorders.

To study diseases of the autoimmune system or to diagnose diseases, the precipitate is analyzed and identified in accordance with the particular disease. For diagnostic or experimental work, the reagent is sold in kit form with instructions for precipitating the immune complexes from specific animals.

It is believed that the reagent is isolated from different animals has substantially the same composition, behaves the same and has a molecular weight of substantially 250,000 to 325,000. It has an anodic and cathodic component with characteristics similar to the rheumatoid factor and Clq complement when subjected to electrophoresis and its activity is affected by heat in a manner similar to these two components and does not bind substantially to monomeric immunoglobulin.

The reagent is obtained from animal sera by removing the salts and precipitating at approximately a pH of 5.5 and by purifying to remove the glycoprotein and lipids until less than 25 percent by weight of the reagent includes contaminants. For the purpose of this definition, contaminants are proteins other than the reagent which bind to monomeric immunoglobulin. The reagent has a molecular weight of 250,000 to 325,000 in the case of a reagent purified from equine sera.

More specifically, pooled equine blood (Central Nebraska Packing, Inc., North Platte, Neb.) is allowed to clot overnight at 4 degrees C. (Centigrade) and the serum collected following 1200.times.g centrifugation. One liter volumes are frozen at -4 degrees C. for storage.

The isolation procedure of the reagent is a modification of the isolation procedure previously described for equine Clq in McDonald, T. L. and Burger, D. Immunol. 37: 517, 1979, the disclosures of which are incorporated herel by reference. In this procedure eight volumes of 0.02M acetate buffer, pH 5.5 are added to 500 ml of equine serum. The mixture remains undisturbed at 4 degrees C. for 15 hours after which the supernatant is siphoned and discarded. The precipitate is washed twice with 5 volumes of acetate buffer and dissolved in 0.5M Tris-HCl buffer, pH 8.2 containing 0.5M NaCl and 0.001 EDTA. This solution (approximately 1/10 of the original serum volume) is clarified at 78,000.times.g for two hours at 4 degrees C.

The clear fluid between the lipid layer and the precipitate is aspirated with a needle and syringe and dialized at room temperature against 0.05M Tris-HCl and 0.001M EDTA, pH 8.2. The resulting precipitate is collected by centrifugation at 1,200.times.g for 15 minutes, washed twice with the dialyzing buffer and dissolved in 0.05M Tris-HCl with 0.001M EDTA and 0.5M NaCl at pH 8.2.

In the next purification step 1 ml aliquots of the dissolved precipitate are applied on a 2.5.times.30 cm Sepharose 6B-Cl column (Pharmacia Chemical Co., Piscataway, N.J.) equilibrated with PBS. Descending flow (30 ml/hour) of solvents is applied by gravity and the eluates monitored at 254 nm to detect protein peaks. The solvents are 0.05M PBS pH 7.2 or 0.05M Tris-HCl containing 0.5M NaCl at 8.2 pH.

The reagent is concentrated by. dialyzing the pooled activity peak against 0.05M Tris-HCl, pH 8.2. The resultant precipitate is redissolved in 0.5M Tris HCl pH 8.2 with 0.25M NaCl, diluted to 2.5 mg protein/ml, aliquoted in 0.5-ml volumes and stored at minus 20 degrees C.

In use, to isolated immune complexes, the reagent binds immune complexes to form a soluble protein complex. This soluble protein-complex precipitates when dialyzed against a high-pH buffer (0.05M Tris-HCl, pH 8.2) and, if it is incubated with serum containing immune complexes, it coprecipitates them. Various immunological assays can then easily determine what kinds and how much immune complexes were in the original material. The antigens may be separated and used: (1) to identify diseases; and (2) in immunotherapy to sensitize leukocytes in vitro and thus to provide marked leukocytes to locate cancer cells or leukocytes to destroy cancer cells.

The reagent, because of unique properties, may be provided in a "kit" form for clinical use. The actual composition of the kit depends upon circumstances of us but ideally contains all accessories such that the assay could be completed in even a modestly equipped clinic. Typically, for a powdered or frozen reagent, it may consist of: (1) 1 ml of RhC at 2.5 mg/ml, frozen or powdered which is enough for 10 assays; (2) 1 vial of Tris-buffer salts to make 1 liter of dialyzing buffer at pH of 8.2; (3) 10 dialysis bags (1 cm.times.5 cm: MW cutoff of 12-14,000); (4) 10 snap-cap micro-fuge centrifuge tubes; (5) 1 vial ammonium acetate salts to make 10 ml of 0.3M final concentration; (6) 1 precut radial immunodiffusion plate; and (7) standard concentration of IgG for determination of standard curve.

It has been found that the reagent may be immobilized on solids such as plastics by ionic attraction without substantial loss of its biological activity. The generally used methods for such immobiliziation of proteins unexpectedly gave unsatisfactory results . For example, the common practive of immobilizing protein onto solid surfaces with either biocarbonate or phosphate buffers at a pH of 9.6 were not sucessful in immobilizing RhC in that the RhC did not retain its biolgoical activity for the binding to immune complexes.

However, it was found that the use of TRIS (Tris 2-amino-2-hydroxymethyl-1,3-propanediol) buffer, provided satisfactory results. In the preferred embodiment 0.05 Molar TRIS with 0.15 molar sodium chloride and 0.001 molar EDTA (ethylene-diamine-tetracetic acid) was used to successfully immobilize the reagent and maintain biological activity. Once the immune complex has been immoblized on a solid surface, standard techniques may be used for its analysis. Thus, the kit may include a solid surface rather than the powder, dialyzing supplies, and centrifuge tubes.

These materials may be packaged together. Moreover, the quantities may in some kits be different and some parts may be omitted for certain applications. The package may be an enclosure capable of holding the parts within it for shipment.

To isolate the RhC reagent from horse serum, 8 volumes of 0.02M acetate buffer are added to one volume of serum at a pH 5.5, while stirring. The pH of the mixture is readjusted to 5.5 with glacial acetic acid and permitted to stand undisturbed overnight at 5 degrees C. The supernatent fluid including the serum is decanted and the precipitate centrifuged at 1,500.times.g for 10 minutes. The precipitate is washed two times in 0.02M acetate buffer, pH 5.5.

The precipitate is dissolved in 0.05M Tris-HCl, pH 8.2 containing 10.sup.-3 M ethylene-diamine-tetracetic acid (EDTA) and 0.5M sodium chloride (NaCl). It is centrifuged at 78,000.times.g for 2 hours at 5 degrees C. and the clear fluid between the upper lipid layer and the precipitate is removed and dialyzed against 2 L of 0.05M Tris-HCl containing 10.sup.-3 EDTA with no NaCl for a minimum of 4 hours at 5 degrees C.

The precipitate is: (1) concentrated by centrifugation at 1,500.times.g for 5 minutes and washed two times with dialyzing buffer; (2) dissolved in minimum volume of 0.05M Tris-HCl buffer, pH 8.2 containing 10.sup.-3 M EDTA and 0.5M NaCl, at which point the volume is usually 1/25 starting volume of serum; and (3) separated by chromatograph on a 40 cm.times.2.5 cm Sepharose 4B-Cl column equilibrated with dissolving buffer.

Equin RhC elutes in the second protein peak and is monitored at 254 nanometers. The entire second Sepharose 4B-Cl eluted peak is collected and dialyzed overnight at room temperature against 0.05M Tris-HCl buffer containing 0.001M EDTA and no NaCl at pH 8.2.

The precipitate is concentrated by centrifugation at 1,500.times.g for 10 minutes and dissolved in minimum volume of 0.05M Tris-HCl containing 0.001M EDTA and 0.25M NaCl pH 8.2, which volume is usually 1/100 original start volume of serum. Each volume of RhC is clarified with 10 volumes of Frigen by vortexing the appropriate volumes at 15 second intervals for 2 minutes and centrifuging 10,000.times.g for 5 minutes. RhC is in the clear fluid layer at the top of the tube.

The clarified RhC is further purified by high pressure liquid chromatography (HPLC) in 0.5M Tris-phosphate buffer at a pH of 8.0 and concentrated by precipitating it with 0.05M Tris-HCl, pH 8.2. This precipitate is dissolved in minimum volumes of 0.05M Tris HCl containing 0.001M EDTA and 0.25M NaCl pH 8.2

The protein concentration of the purified equine RhC is determined and diluted to 2.5 milligrams/ml using the final dissolving buffer above. It is broken into aliquotes and frozen at -20.degree. C. This purified RhC is used for the isolation of immune complexes from serum without further treatment.

To isolate the circulating immune complexes from serum, equal volumes of the serum of the animal and the reagent are mixed. A stock reagent has typically a concentration of two and one-half milligram of protein for each milliliter. A typical mixture may consist of 100 microliters of the sera taken directly from the animal and the 100 microliters of the reagent.

The mixture is placed in polystyrene tubes and incubated for 15 minutes at 37 degrees Centigrade and the contents ar then dialyzed against two liters of 0.05M Tris-HCl at a pH of 8.2 for two hours. This process removes a substantial portion of the salts from the serum and the material is then centrifuged at 1,200 gravities for five minutes and the precipitate resuspended and washed twice in the dialyzing buffer.

The final precipitate is dissolved in 100 microliters of 0.05M Tris-HCl at a pH o 8.2 or 0.3M ammonium acetate at a pH 7.0. The solution is analyzed by rocket immunoelectrophoresis or radial immunodiffusion respectively.

The amount of immune complex which is isolated is indicative of disorder. It differs from species to species: but in humans, a range of between 12 to 15 micrograms of immune complex per milliliter of undiluted serum or plasma is normal. This is within accuracy of 5 micrograms. Variations from 12 to 15 microgram levels indicate a disorder.

To determine the accuracy of the tests, each sample is divided into 10 aliquotes and each aliquote has the immune complex isolated. The measurements have a precision with a standard deviation of plus or minus 4 micrograms per milliliter.

The RhC factor in the immune complexes is separated by affinity chromatography by binding the immune complexes to staphylococcus protein-A (SPA) in the packing of the column or by HPLC. In the case of SPA, the immune complexes are then eluted by one of the following solvents, 0.1M glycine-HCL, pH 3.2, 1.0M sodium thiocyanate, pH 7.2 or 0.5M diiodosalicylic acid, pH 7.5 and the antigens separted by electrophoresis. The elctrophoresis mobilities may be used to identify the antigen or the antigen may be separated for other analysis.

After separation, the antigens from the immune complexes can be analyzed for composition by a variety of techniques such as by high performance liquid chromatography or SDS (sodium dodecylsulfate) polyacrylamide gel electrophoresis (SDS-PAGE). An antigen profile may be determined for certain particular diseases and used to identify a particular disease. Preparation of antibodies to common antigens of the diseased can aid in detection and diagnosis and eliminate the interference of unrelated immune complexes or antigens.

A specific procedure for diagnosing diseases may include the steps of: (1) screening serum samples for presence of immune complex by the techniques described previously for RhC; (2) obtaining more serum from patients having large amounts of immune complexes; (3) separating immune complex from RhC by affinity chromatography (RhC does not bind), or HPLC; (4) separating the immune complexes into antigen and antibody components by an electrophoresis; (5) analyzing antigens from the immune complexes for composition by one of a variety of known techniques such as high performance liquid chromatography or SDS-PAGE; (6) developing an "antigen profile" of circulating IC for each patient with the same disease; and (7) prepare antibodies to the "disease-common" antigen or antigens in the patients from the profile.

The antibodies may be used for diagnosis of the disease in other patients by detecting the antigen in the blood samples of the other patients. Moreover, marked antibodies may be prepared. to locate antigens in the subJect or leukocytes sensitized to destroy antigens.

The invention is illustrated by the following examples:

In the preferred embodiment equine RhC reagent is used although an RhC reagent with the same properties has been purified from the serum of other animals including human beings, rabbits and cattle. To prepare the reagent, eight volumes of 0.02 acetate buffer is added to one volume of horse serum at a pH 5.5 while stirring. The pH is readjusted to 5.5 with glacial acetic acid and permitted to stand undisturbed for several hours at 5 degrees centigrade.

A precipitate is formed at this step; and it is believed that white precipitate obtains the reagent. The reagent has activity similar to that of a rheumatoid. factor and a Clq complement component. The reagent is purified to remove other materials and specifically lipids as follows.

Firstly, the serum is decanted and the precipitate is centrifuged at 1,500.times.g for 10 minutes. It is then washed two times on 0.02M acetate buffer at a pH of 5.5.

Secondly, the precipitate is dissolved in 0.05M Tris-HCL (tris-hydrosy-methyl)amino methane with 0.05M hydrochloric acid added to adjust its pH to 8.2. The Tris-HCL contains 0.001M ethylene-diamine-tetracetic acid (EDTA) and 0.5M sodium chloride (NaCl). This solution will have approximately 1/10 of the original starting volume of the serum.

Thirdly, the resulting solution is centrifuged at seventy-eight thousand gravities for two hours at 5 degrees centigrade. The clear fluid between the upper lipid layer and the precipitate is removed and dialyzed against two liters of 0.05M Tris-HCL containing 0.001M EDTA but with no sodium chloride for a minimum of four hours at 5 degrees centigrade.

Fourthly, the precipitate from the previous step is concentrated by centrifugation at 1,500 gravities at five minutes and washed two times with the same dialyzing buffer used above.

Fifthly, the precipitate is dissolved in a minimum volume of 0.5M Tris-HCL buffer at a pH of 8.2 containing 0.001M EDTA and 0.5M sodium chloride. It is now usually at 125th of the starting volume of the serum.

Sixthly, the resulting solution is purified further on a liquid chromatograph using 40 centimeters by 2.5 centimeters Sepharose 4B-CL column equilibrated with 0.05M Tris-HCL buffer. Equine RhC elutes in the second protein peak monitored at 254 nanometers with a solvent of 0.05M Tris-HCL at a pH of 8.2 containing 0.001M EDTA and 0.5M sodium chloride. The solution forming the second protein peak is collected and dialyzed for several hours at room temperature against a 0.05M Tris-HCL buffer containing 0.001M EDTA but without sodium chloride. The buffer is maintained at a pH of substantially 8.2 to form a further purified white precipitate.

Seventhly, the precipitate is concentrated by centrifugation at 1,500 gravities for ten minutes and dissolved in a minimum volume of 0.05M Tris-HCl containing 0.001M EDTA and 0.25M sodium chloride at a pH of 8.2. At this point the volume is approximately 1/100ths of the original starting volume of the serum.

Eighthly, more of the lipids are removed by taking each volume of RhC and clarifying it with 10 volumes of Frigen (1,1, 2-Trichlorotrifluroethane) by vortexing the appropriate volumes at 15-second intervals for two minutes and centrifuging at 10,000 gravities for five minutes. The RhC is in the clear fluid layer at the top of the tube and this clear fluid layer is removed from the foamed material created by the vortexing.

Finally, the clarified RhC is further purified by high pressure liquid chromatography (HPLC) in 0.5M Tris-phosphate buffer, at a pH of 8.0 and concentrated by precipitating it with 0.05M Tris-HCl, pH 8.2. This precipitate is dissolved in minimum volumes of 0.05M Tris HCl containing 0.01M EDTA and 0.25M NaCl pH 8.2.

At this stage, the reagent is sufficiently pure and is prepared to an appropriate concentration. The protein concentration of the purified RhC is determined and diluted to 2.5 milligrams of RhC for each milliliter in 0.05M Tris-HCl containing 0.001M EDTA and 0.25M sodium chloride at a pH of 8.2 It may be broken into aloquotes and frozen at a negative 20 degrees Centigrade. At this step the reagent protein contains about 300 parts for every part of lipid or other contaminating material in the solution.

To remove lipids, two ml of 1, 1, 2-Trichlorotrifluroethane (Frigen) is added to 0.25 ml of serum and mixed with vortex at 15 second intervals for total mixing time of 2 minutes. It is centrifuged at 1,500.times.g for 5 minutes and 0.1 ml of lipid-clarified serum is removed and placed in a clean glass tube.

To isolate immunglobulin complexes, 0.1 ml of RhC reagent is added to each 0.1 ml of Frigen-Treated serum to be assayed for IC and the solution is incubated at 37.degree. C. for 30 minutes.

The contents of each tube is removed and dialyzed against 1 liter of 0.05M Tris-HCl buffer containing 10.sup.-3 M ethylene-diamine-tetra-acetic acid (EDTA) for two hours. The contents of each dialysis bag is removed with a pasteur pipette, and the bag is washed nce with dialyzing buffer and centrifuged at 8,000.times.g for 5 minutes.

The supernatant is discarded and precipitate washed two times with dialyzing buffer. The precipitate is resuspended well by vigorously pipetting up and down with the bulbed-pasteur pipette.

The final precipitate is dissolved in 0.1 ml of 0.3M ammonium acetate (AA) pH 7.0.

To determine the amount of immune complex, the isolated-IC is diluted 1:2 and 1:4 by adding 0.025 ml of sample to 0.025 ml of AA and 0.025 ml of sample to 0.075 ml of AA respectively.

Five microliters of each dilution and 5 microliters of solution of standard concentrations of IgG (10, 25, 40 and 60 micrograms/ml) are placed in wells of a radial immunodiffusion plate containing 0.2% of anti-IgG and incubated at room temperature for 18 hours.

The plate is soaked in distilled water for 1 hour, dried in warm air and stained.

A standard curve is drawn by measuring the diameter of the diffusion rings obtained for the IgG standards and plotting these measurements against their respective concentration. The concentrations IgC in immune complexes of unknown samples is determined by measuring the diameter of the diffusion ring, interpreting from the standard curve and multiplying by the appropriate dilution.

Another method of assaying antibody contained in the RhC-isolated immune complexes is a modification of the rocket immunoelectrophoresis (RIEP) originally described in Laurell, C. B. (1972) Electroimmuno. assay, Scand. J. Clin. Invest 29, 21, the disclosure of which is incorporated herein. This method is used for the quantitation of immunoglobulin classes and subclasses in both the original serum samples and the reagent precipitates.

Prior to gel casting, the appropriate antisera with specificity to the immuhoglobulin (Research Prod. Int., Elk Grove Village, Ill.) is diluted to 1% v/v final concentration in 56.degree. C. agarose (1% w/v in barbital buffer, pH 8.6). All serum samples are diluted 1:40 in 0.05M phosphate buffered saline at a pH 7.2 with undiluted immune complex isolates are incubated 30 min. at 37.degree. C. with an equal volume of 1% formaldehyde prior to RIEP. Five ul aliquotes are then applied to 3 mm diameter wells, cut at the base of the gel slab, and immediately electrophoresed at 5 volts/cm gel for 4 hours at 4.degree. C.

Five ul samples of IgM, IgG.sub.1 and IgG.sub.2 (Research Prod. Int., Elk Grove Village, Ill.) are used as standards at concentrations of 200, 100, 50 and 25 ug/ml. Following RIEP, the gel plates are dried and stained with 0.05% w/v Coomassie brilliant blue R-250 and destained with ETOH, H.sub.2 O, glacial acetic acid (4.5: 4.5:1.0) as described by Laurell supra.

The reproducability of the reagent in isolating CIC from infected and normal animals was evaluated by analysis of frozen aliquots of each pooled serum sample at three different times. The greatest standard error of the mean concentration of CIC in these triplicate serum samples is calculated. Analysis of individual samples, run in triplicate, is made to assess the reproducability of the RIEP for analysis of CIC concentration, and the standard error is calculated.

The sensitivity of the RIEP was determined by electrophoresing varius concentrations each immunoglobulin class or subclass against the appropriate homologous antisera-containing gel. The lowest detectable concentration is determined for all IgG subclasses.

Virus. Frozen LDV (lactic dehydrogenase virus) infected mouse serum was originally obtained from Dr. D. Burger, Washington State University, Pullman, Wash. and used as seed virus. Stock virus preparations, titrations and storage were performed as described by Rowson and Mahy, 1975, (supra).

Mice. Balb/c mice (Charles Rivers Labs., Wilmington, Mass.) were caged in 10 groups of 7 each and infected with 0.1 ml of stock LDV by intraperitoneal injection. Chronological samples were obtained daily by pooling approximately 0.5 ml of blood, obtained by retroorbital sinus puncture, from all mice in one cage. The serum collected following low speed centrifugation was assayed immediately for lactic dehydrogenase activity (LDH) and the remaining serum pool was frozen at -70.degree. C. in 0.5 ml alioquots.

Using this method, each group of mice was bled every 10 days and all 10 cages were maintained throughout one 33 day chronological study. Alternate daily bleedings of three cages of 7 uninoculated Balb/c mice were used for normal mouse serum pools. All uninoculated animals were housed separately from LDV mice. CIC were isolated from chronological serum samples from LDV-infected mice as described above.

A modification of the rocket immunoelectrophoresis (RIEP), described above, is used for the quantitation of immunoglobulin classes and subclasses in both the original serum samples and the RhC precipitates.

The greatest standard error of the mean concentration of CIC in these triplicate serum samples was .+-.6 ug/ml (range .+-.2 ug to .+-.6 ug). Analysis of individual samples run in triplicate, in order to assess the reproductability of the RIEP for analysis of CIC concentration, demonstrated a standard error of .+-.4 ug/ml.

The sensitivity of the RIEP was determined as described above, and the lowest detectable concentration was 5 ug/ml for IgM and 10 ug/ml for all IgG subclasses.

An indirect ELISA method was used to quantitate anti-LDV activity in the chronological serum samples obtained from LDV-infected mice. Diluted samples containing isolated CIC were incubated in ELISA wells that were previously coated with purified LDV antigen and the date scored for anti-LDV activity following addition of alkaline phosphatase-conJugated anti-mouse IgG as the ELISA second antibody as described above.

No anti-LDV activity was detected in any of the samples containing isolated CIC. This indicates that the LDV-specific antibody demonstrated in the isolated CIC by RIEP was bound to the LDV-antigen.

IC were isolated from the serum of diabetic and normal hamsters by coprecipitation with the reagent, RHC as described in the general section.

Syrian hamsters at six weeks of age and approximately 100 g in weight were injected intraperitoneally, once each day for three days with 50 mg streptozotocin (SZ) per kg of body weight. Age-matched animals were similary injected with acidified saline and were used as controls.

All hamsters had free access to water and lab chow however none of the animals received insulin. Serum samples were obtained from blood that was drawn from the orbital sinus of each hamster at weekly intervals. Serum glucose was determined with a Beckman II glucose analyzer. Only those animals with fasted-glucose concentrations of greater than 300 mg/dl were considered to be diabetic. The serum was stored at -70.degree. C. for future us in IC assays.

Immune complexes isolated from the serum of the Sz-induced diabetic hamsters by coprecipitation with RhC comprised an unknown antigen and IgG at two distinct time intervals during the 12-week chronological study. Although all diabetic hamsters with hyperglycemia of 300 mg/dl had IC, there was no correlation between the occurrence or concentration of IC and the degree of hyperglycemia.

The isolation of IC from diabetic and normal hamster serum by equine RhC was shown to be highly reproducable by analysis of frozen aliquots of the same serum sample at three different times. It has a coefficient of variations (CV) of 1.6%. Interexperimental variation in the RIEP analysis of triplicate samples was also highly reproducable (CV of 1.2%). The lowest detectable concentration of IgG by RIEP was 25 ug/ml and defined the lower limits of the test system.

Anti-BSA was prepared by subcutaneous inoculation of 5 rabbits, each received 2 mg BSA dissolved in 1 ml of PBS - Freund's complete adjuvant and each was boosted 3 weeks later with the same BSA concentrations in Freund's incomplete adJuvant. Anti-BSA activity of these was determined by the highest titer at which a visible precipitin line was seen in an Ouchterlony-type gel diffusion system. Rabbit sera having an Ouchterlony titer of 16 or greater 2 weeks following booster inoculations were pooled and stored at -20.degree. C. for IC preparation.

.sup.125 I-HG was prepared by pooling the non-aggregated protein peak eluted from a Sephadex G-200 column (Pharmacia Chemical Co., Piscataway, N.J.) loaded with 10 mg/ml .sup.125 I-labeled unheated Cohn Fraction II.

Radiolabeling of both human IgG and BSA wa performed as described in Enzymobead radioiodination reagent bulletin (Bio-Rad Laboratories, Richmond, Calif.) The labeled protein was exhaustively dialyzed at 4.degree. C. against pH 7.2 PBS to remove unbound .sup.125 I.

IC were prepared in PBS by adding .sup.125 I-BSA and rabbit anti-BSA in the desired Ag-Ab ratios. The anti-BSA serum was diluted 1:4 and incubated with decreasing concentrations of .sup.125 I-BSA in order to determine Ag-excess, Ag-Ab equivalence, Ab excess and percent soluble IC.

AHG was prepared by heating 2.0 ml of a 20 mg/ml solution of .sup.125 I-Cohn Fraction II (Sigma Chemical Co., St. Louis, Mo.) at 63.degree. C. for 20 min. Insoluble aggregates were removed by 1,200.times.g centrifugation for 15 min and the supernatant applied to a 1.5.times.25 cm Sephadex G-200 column equilibrated with PBS. AHG that eluted in the void volume was pooled, aliquoted and frozen at -70.degree. C.

The ability of the RhC factor to co-precipitate bound as opposed to unbound IgG is demonstrated with .sup.125 I-labeled Cohn Fraction II in aggregated (AHG) and unaggregated (HG) states following the procedure for above for isolating immune complexes.

To establish if the RhC factor was a limiting factor for the isolation of Ag-Ab complexes, it was necessary to determine the optimum concentration required to co-precipitate a predetermined amount of AHG. Radiolabeled AHG and HG were diluted to approximately 45 ug (micrograms) of protein contained in 100 ul (microliters) of PBS and was represented by approximately 2.22.times.10.sup.5 cpm. To these 100 ul samples, 100 ul of RhC varying in protein concentration from 100 ug/ml to 1 mg/ml was added.

To determine the efficacy of the RhC factor to coprecipitate soluble Ag-Ab antigen-antibody) complexes in Ag or Ab excess, the following in vitro BSA anti-BSA model system was used, using the above materials. In this series of experiments, the BSA anti-BSA model was defined with respect to Ag-Ab equivalence (maximum insoluble IC) and the percent soluble IC.

One-half ml of a 1:4 dilution of rabbit anti-BSA serum was incubated with an equal volume of two fold serial dilutions of .sup.125 I-BSA for 1 hr at 37.degree. C. Following 1,200.times.g centrifugation for 15 min the percent of insoluble BSA-anti-BSA immune complexes was determined. In our system Ag-Ab equivalence was reached at 64 ug/ml of .sup.125 I-BSA which precipitated approximately 93% of the available BSA antigen. The percent of soluble immune complexes represented by the total .sup.125 I remaining in the 1 ml supernatants was calculated by (NH.sub.4).sub.2 SO.sub.4 precipitation analysis on one-half of the sample volume. From a concentration range of 125 ug of BSA (2.times.antigen excess) to 8 ug BSA (8.times.antibody excess) approximately 85% of the .sup.125 I BSA in solution was a soluable IC. The remaining one-half (500 ul) of the .sup.125 I BSA anti-BSA supernatants was incubated with 500 ul of the Rhc.

At Ag-Ab equivalence and all conditions of Ab excess, 100% of the soluable BSA-anti-BSA IC was coprecipitated with the RhC factor. Under conditions of 2.times.Ag excess approximately 80% of the soluable IC were coprecipitated and minimal isolation could be obtained at Ag concentrations greater than 8.times.. Dialysis of these soluable IC-containing solutions without addition of RhC factor resulted in no precipitation of radioactivity. In addition, the RhC would no coprecipitate free .sup.125 I BSA that was not bound as an IC.

Heat-aggregated human IgG (AHG) and monomeric human IgG (HG) were also subjected to IC-isolation by RhC. The percentage of labeled IgG that coprecipitated with the RhC following dialysis was calculated from the .sup.125 I-protein specific activity and the results are expressed in Table 1.

Increasing concentrations of RhC material did not affect the co-precipitate of HG. In control experiments, neither AHG or HG precipitated without the addition of the RhC. It was determined from these results that the RhC diluted to 2.5 mg/ml would be used with equal volumes of IC samples for maximum efficiency.

The RhC reagent co-precipitated 99% of the .sup.125 I-labeled aggregated human IgG (AHG) following dialysis against 0.05M Tris-HCl, pH 8.1 compared to only 0.8% of the unaggregated human IgG (HG). When incubated with bovine serum albumin (BSA) anti-BSA soluble immune complexes (IC) prepared at antigen (Ag)-antibody (Ab) equivalence or in Ab excess, the RhC co-precipitated 100% of the available complexes. Under conditions of 2.times.Ag excess, RhC was less efficient as demonstrated by co-precipitation of 80% of the available IC.

Serum from patients clinically normal was processed by the isolation of immune complex procedure in the general section and reproducibility was checked by the procedure in the general section above.

The level of immune complexes isolated for all twenty-five patients fell within the range of 12-18 micrograms with the mean amount being 15 micrograms to provide a standard error of 5 micrograms.

Serum from 36 patients who had been diagnosed a having diabetes with late complications was obtained and the immune complexes separated from it as described under Isolation of Immune Complexes above. The reproducibility of the measurements was tested as described in the section under reproducibility by rocket immunoelectrophoresis or radio immunodiffusion.

Of the 36 patients clinically diagnosed a having diabetes, 34 showed an elevated level of immune complexes. The total range was from a normal range of 15 micrograms to 144 micrograms. The standard deviation on the repeated samples was plus or minus 6 micrograms.

Serum from 37 patients who had been clinically diagnosed as having streptococcus infection was drawn and the immune complexes separated in the manner decribed in the general section of the examples. The reproducibility was checked by the procedure described in the general section.

The level of the immune complexes of 22 of the 37 samples was elevated above normal. The range of immune complexes was from 14 micrograms to 280 micrograms with a standard deviation on repeated samples of plus or minus 5 micrograms.

Serum from 6 patients clinically diagnosed as being infected with streptococcu with bacteremia was obtained and the immune complexes isolated in accordance with the procedure in the general section. The reproducibility was checked in accordance with the procedure under Reproducibility in the general section.

Six of the six patients had immune complexes above a normal level. The range of immune complexes was 140 micrograms to 260 micrograms with a standard deviations on repeated samples of plus or minus 6 micrograms.

Serum was obtained from 2 patient diagnosed as having juvenile rheumatoid arthritis in an active stage and immune complexes were isolated following the procedure in the general section of these examples. The reproducibility was tested as stated in the general section.

Both of the samples showed elevated levels of immune complexes, with both of them showing 240 micrograms.

Serum was obtained from 2 patients diagnosed as having had juvenile rheumatoid arthritis which was in remission. The immune complexes were isolated as described in the general section of these examples.

Neither of the patients showed elevated levels of immune complexes as compared to the levels of Example 5 for clinical diagnosis of normal patients. The levels were between 12 and 15 micrograms.

Samples of serum were obtained from 3 patients clinically diagnosed as having acute nephritis. The samples were processed for the isolation of immune complexes using the procedure described in the general section of these examples.

All three of the patients showed elevated levels of immune complexes within the range of 90 micrograms to 120 micrograms.

Samples were obtained from 2 patients clinically diagnosed as having bacterial endocarditis and the immune complexes were isolated using the procedure provided in the general section of these examples.

Both patients showed elevated immune complexes within the range of 140 micrograms to 180 micrograms.

Immune complexes were isolated from the serum of rats with streptozotocin-induced diabetes. One method using RhC as described in the general section and the other using an affinity chromotography with human polyclonal rheumatoid factor being attached to the packing. Both methods precipitated immunoglobluin but the affinity chromotography method isolated both bound and monomeric immunoglobulin whereas the method described in this section precipitated only quantities of immune complexes without monomeric immunoglobulin.

Samples of serum were obtained from 20 mice without tumors and the immune complexes isolated using the procedure described in the general section of these examples. The immune complexes were not elevated. Twenty mice with bladder tumors had samples drawn from them at periods of one week, two weeks, and three weeks.

In the fourth week, the tumor was removed from 10 animals and the immune complexes measured from serum in four weeks for both the 10 animals with the tumor removed and the 10 animals in which the tumor remained. All ten animals with tumors died between the fourth and the fifth week. It was noted that the primary tumor had metastasized to the lungs.

Serum was drawn from animals with the tumor removed at the fifth week. The immune complexes were isolated using the procedures in the general section and the reproducability was measured using the procedures in the general section of these examples.

The mice without tumors showed no elevation of immune complexes. The animals with tumors showed a mean value of immune complex of 55 micrograms with a standard deviation of plus or minus eight micrograms in the frist week, a precipitation of immune complexes of 80 micrograms with a standard deviation of 5 micrograms in the second week, a level of immuhe complexes isolated of 170 micrograms with a standard deviation of plus or minus 6 micrograms in the third week

In the 10 animals for which the tumor was removed in the fourth week, the average of the immune complexes was 25 micrograms with a standard deviation of plus or minus 6 micrograms: and in the tumored animals it was 180 micrograms with a standard deviation of 5 micrograms. Of the animals with the tumor removed, in the fifth week, was 80 micrograms with a standard deviation of plus or minus 5 micrograms.

From the above decription, it can be understood that the technique and reagent of this invention has several advantages such as: (1) the reagent is inexpensive and easy to use to quantitate immune complexes; (2) the technique enables a simple and inexpensive diagnostic possibility for disease; (3) the reagent may be sold separately to laboratories who may perform the diagnosis at their laboratories without the use of expensive equipment; (4) the technique is specific and accurat in quantitative determination of immune complexes; (5) the reagent precipitates sufficient quantities of immune complex for analysis; (6) the technique permits a relatively simple quantitative isolation of immune complexes from serum; and (7) the technique produces better results at a lower cost.

Although a preferred embodiment has been described with some particularity, many modifications and variations may be made in the preferred embodiment without deviating from the invention. Accordingly, it is to be understood that, within the scope of the appended claims, the invention may be practiced other than as specifically described.