MOLECULAR-CLONING AND CHARACTERIZATION OF THE GENES-CODING FOR THE HIGHLY IMMUNOGENIC CLUSTER OF 90-KILODALTON ENVELOPE PROTEINS FROM THE CHLAMYDIA-PSITTACI SUBTYPE THAT CAUSES ABORTION IN SHEEP

Proteins present in the outer membrane of chlamydiae that are involved in mucosal epithelial cell infection must clearly be identified and c haracterized if we are to understand and modify the pathogenic mechani sms utilized by these organisms. We have identified and isolated a fam ily of four genes encoding putative outer membrane proteins (POMPs), a group of proteins of approximately 90 kDa present in the outer membra ne of the subtype of Chlamydia psittaci that causes ovine enzootic abo rtion (strain S26/3). These proteins, although minor components, are m ajor immunogens, as shown by the immunoblotting of chlamydial outer me mbrane complexes with postabortion sheep sera, and are therefore poten tial diagnostic and/or protective antigen candidates, Immunoblotting o f the expressed amino-and carboxy-terminal halves of one of the POMPs with postabortion sheep sera showed that the major humoral immune resp onse appeared to be directed solely against the amino-terminal half Th is result, in combination with the positive immunofluorescence stainin g of S26/3-infected cells using POMP-specific (specific to the amino t erminal half of the proteins) monoclonal antibodies, suggests the prob able surface localization of the POMPs and, more specifically, the sur face exposure of the amino-terminal half of these proteins. The four p omp genes are highly homologous, sharing 82 to 100% similarity with ea ch other (two of the genes are identical), Genes with strong and weak homologies were also detected in C. psittaci avian and feline pneumoni tis strains, respectively. No pomp homologs were found in strains of C . trachomatis and C. pneumoniae, but this does not preclude their exis tence, The absence of homology with various subtypes of C. pecorum, wh ich complicate the diagnosis of the ovine abortion subtype, indicates the possible suitability of the these 90-kDa proteins as serodiagnosti c antigens.