Properties of monoclonal antibodies to the genus-specific antigen of Chlamydia and their use for antigen detection by reverse passive haemagglutination.

The chlamydial genus-specific antigen was extracted with phenol/chloroform/petroleum ether (PCP) from preparations of Chlamydia trachomatis and C. psittaci, and quantities measured using an assay for lipopolysaccharide (LPS). The LPS from C. trachomatis contained 2.2% (w/w) of ketodeoxyoctanoic acid. Five IgG monoclonal antibodies reacted in an ELISA with LPS from both species, the antigen being periodate-sensitive and heat-resistant, confirming that all antibodies were against the genus-specific antigen. All the antibodies bound to the PCP extract of C. trachomatis on an immunoblot, at a position corresponding to the periodate-Schiff-stained bands of both C. trachomatis extract and Salmonella Re-LPS. When linked to trypsin-treated sheep erthrocytes and used in reverse passive haemagglutination tests, all antibodies gave indicator cells capable of detecting chlamydial LPS or crude preparations of chlamydiae grown in McCoy cells, the sensitivity varying with the antibody used. The antibodies varied in IgG subclass (either IgG2a or IgG3), and in ability to precipitate in immunodiffusion tests. Two antibodies cross-reacted with one strain of Acinetobacter in ELISA and with Salmonella Re-LPS in both ELISA and immunodiffusion tests. The other three did not react in ELISA with Acinetobacter strains or Salmonella Re-LPS, and none of the five reacted with LPS of E. coli or Pseudomonas morsprunorum.