Detection and antigenicity of chlamydial proteins that blind eukaryotic cell membrane proteins

Chlamydia psittaci proteins capable of binding eukaryotic cell membranes were identified and antigenically characterized. Cell membrane proteins (CMP) of noninfected cells were labeled with biotin (B-CMP), then were extracted with 1% Triton X-100. Nitrocellulose membrane strips containing sodium dodecyl sulfate-polyacrylamide gel electrophoresis-resolved proteins of chlamydial elementary bodies (EB) were reacted with the B-CMP extract, followed by addition of streptavidin-conjugated horse radish peroxidase. Among the various strains of chlamydiae examined, a protein of approximately 16 to 18 kDa consistently bound B-CMP. A second larger protein, ranging in molecular mass from 24 to 32 kDa, also bound B-CMP. Immunoblotting techniques were used to analyze the reactions of antisera from immunized and experimentally infected animals to these proteins. A rabbit polyclonal antiserum produced against the 18-kDa adhesin of a serovar-1 strain of C psittaci (B577) reacted strongly with 18-kDa proteins of aH C psittaci strains, but weakly with that of C trachomatis. Mouse antisera raised against the serovar-2 (FCc-Stra) 28-kDa protein reacted only with proteins of the homologous serovar. Sera from experimentally infected animals did not react with the C trachomatis 18-kDa adhesion protein, but did react in 2 patterns with related and nonrelated C psittaci isolates. Two rabbits inoculated with infective serovar-1 EB and 1 rabbit inoculated with a serovar-2 strain reacted specifically with the 18-kDa proteins of their homologous serovars. In contrast, 2 other rabbits inoculated with the same serovar-2 strain produced antisera that reacted with all C psittaci 18-kDa proteins, as did serum from a similarly inoculated buff. The reason for the 2 types of responses to infection remains to be determined.