Recombinant Clones of Chlamydia Trachomatis Lipopolysaccharide

Chlamydia are obligate intracellular procaryotes that are structurally similar to gram-negative bacteria. There are two species, Chlamydia trachomatis and C. psittaci. C. trachomatis is a specific human pathogen, whereas C. psittaci is a pathogen of a variety of non-primate species. Diseases caused by C. trachomatis present a major health problem throughout the world. In developing countries, C. trachomatis causes hyperendemic trachoma which is the world's leading cause of preventable blindness. There are approximately two million people in the world today who are blind as a result of trachoma and an estimated 500 million more who are affected by this disease. In industralized nations, C. trachomatis is a sexually transmitted pathogen that causes an array of genital tract and associated infections whose incidence is increasing at epidemic rates. Conservative estimates indicate that in the United States alone there are 7-10 million C. trachomatis infections per year. In addition to their vertebrate hosts, chlamydial-like organisms have also been identified in tissues of spiders (Coelotus luctuosus) and clams (Mercenarie mercenaria), suggesting that chlamydiae are ubiquitous parasites present throughout the animal kingdom.

Biologically, Chlamydia are distinguished from all other intracellular procaryotes by their unique life cycle and molecular mechanisms of pathogenesis. The life cycle consists of two cell types, the elementary body and the reticulate body, which differ both morphologically and functionally. The elementary body is the extracellular cell type; it is metabolically inactive and is the infectious form of the parasite. The elementary body is unique in that it is efficiently phagocytized, even by nonprofessional phagocytes, and once internalized, it prevents phagolysosomal fusion. Mediators of these pathogenic mechanisms are believed to be surface components of the elementary body; however, their identity and biochemical nature is currently unknown.

Despite their common biology, C. trachomatis and C. psittaci share only 10% DNA homology and demonstrate little antigenic relatedness among their surface protein constituents. They do, however, share a common outer membrane qlycolipid antigen that has been shown to be a lipopolysaccharide (LPS) antigenically similar to the Re LPS chemotype isolated from mutants of Salmonella spp. (Caldwell et al: Inf. & Imm. 44 : 306-314 [1984]). Despite the similarities between chlamydial LPS and the Re LPS of enteric bacteria, chlamydial LPS contains a periodate sensitive antigenic determinant that is common to Chlamydia but is not found in a variety of enteric bacteria. This antigenic determinant has been defined by monoclonal antibody and termed the genus-specific LPS antigen (see Caldwell et al, above). The biological function of chlamydial LPS is unknown, but the conserved nature of the LSP epitope in an otherwise antigenically diverse genus suggests that this epitope may be functionally important with respect to the molecular mechanisms of pathogenesis shared by these obligate intracellular parasites.

The clone JM109(pFEN207), equivalent to ATCC Accession No. 53041, was deposited in the American Type Culture Collection on Feb. 27, 1985, in the patent deposit for a term of at least thirty years and complying with the time requirements of the Budapest Convention.

The recombinant clones of the present invention are used for the development of simple, rapid, and inexpensive serologic or antigen assays for diagnosing and treating infections caused by Chlamydia trachomatis or C. psittaci.

The clones of the present invention are produced from chlamydia a gene bank selected from, a C. trachomatis was partially digested with Sau3A. DNA of 4-6 kilobases is pooled and then cloned into BamHI digested alkaline phosphatased E. coli pUC8. These clones possess an antigen reactive with monoclonal antibodies directed against the genus-specific LPS epitope.

Whole genomic DNA from C. trachomatis is isolated and digested partially with Sau3A restriction enzyme. Partially digested DNA is then sized by agarose gel electrophoresis; DNA of 4-6 Kb is isolated, pooled, and ligated into a suitable BamHI digested plasmid. The ligated plasmid mixture is then transformed into E. coli, and ampicillin resistance E. coli were selected (indicating recombinants containing C. trachomatis DNA). They are then screened for the presence of chlamydial specific antigens using polyclonal antibody directed against C. trachomatis elementary bodies. Several E. coli recombinants reacted with the antibodies: these are then screened with monoclonal antibodies directed against different antigens. Several of the recombinants reacted with lipopolysaccharide epitope of C. trachomatis (also found of C. psittaci) and these recombinants were further characterized by examining the DNA with restriction endonucleases in vitro transcription translation of the isolated plasmid and other biochemical techniques.

A preferred plasmid for use in this process is pUC8, commercially available from Pharmacia. pUC8 and other suitable plasmids, contain a relatively strong promoter region which aids in expression of the chlamydial genes. Specifically, this promoter is the lac operon promoter.

A preferred strain of E. coli is strain JM109, also commercially available. This particular strain is compatible with pUC8 due to a lesion of the lac operon on the chromosome.

Although a preferred plasmid and bacterial strain are disclosed, other plasmids and E. coli strains may be used provided that the plasmid contains a lac promoter and the E. coli strain complements the plasmid.

An experiment was conducted to determine whether the chlamydial LPS epitope was exposed on the surface of the E. coli recombinant. Fluorescent antibody staining of heat-fixed pFEN207 cells with the chlamydial LPS monoclonal antibody showed that the antigen was located at the periphery of individual cells.

Surface immunofluorescence was also observed. Surface exposure of the chlamydial LPS epitope was shown on viable E. coli recombinants by immunoelectron microscopy. When viable pFEN207 cells were reacted with monoclonal antibody and protein A colloidal cold and then examined by electron microscopy without subsequent fixation or staining, electron dense gold particles were specifically bound to the surfaces of the recombinant clone expressing the chlamydial LPS epitope.

From a gene bank of C. trachomatis (strain LGV-434) DNA, we identified several recombinants that were immunoreactive with rabbit polyclonal antibody raised against viable LGV-434 elementary bodies. Four of these non-sibling recombinants were subsequently shown by immunoblots of polyacrylamide gels to possess an antigen reactive with monoclonal antibody directed against the genus-specific LPS epitope. One of these Escherichia coli recombinants, JM109 (pFEN207), was studied in more detail. Analysis of whole-cell preparations and phenol-water extracts of chlamydial elementary bodies and E. coli recombinants by polyacrylamide gel electrophoresis showed that the JM109 (pFEN207) recombinant possessed three distinct species of LPS. Two of the LPS species were found in the parent E. coli strain harboring the pUC8 plasmid. A third LPS species was unique to the recombinant strain and reacted with monoclonal antibody against the chlamydial genus-specific LPS epitope by immunoblotting analysis. The immunoreactive LPS found in the recombinant clone pFEN207 migrated with an increased electrophoretic mobility relative to native chlamydial LPS. This molecule is a hybrid LPS composed of both an E. coli and chlamydial LPS component. The pFEN207 plasmid contains a gene(s) that encodes a glycosyl transferase involved in chlamydial LPS synthesis and that the chlamydial glycosyl transferase has incorporated the carbohydrate moiety that confers the genus-specific antigenic property to chlamydial LPS on E. coli LPS.