CHARACTERIZATION OF THE MURINE ANTIBODY-RESPONSE TO PEPTIDES REPRESENTING THE VARIABLE DOMAINS OF THE MAJOR OUTER-MEMBRANE PROTEIN OF CHLAMYDIA-PNEUMONIAE

In an attempt to gain more knowledge about the immunogenicity of the v ariable domains (VDs) of the major outer membrane protein (MOMP) of Ch lamydia pneumoniae, peptides representing these areas were used to imm unize BALB/c and C57BL/6 mice. Antisera to the peptides and to peptide s conjugated to keyhole limpet hemocyanin (KLH) were characterized by their ability to recognize the immunizing peptide and elementary bodie s (EBs) of C. pneumoniae by enzyme-linked immunosorbent assay (ELISA) and Western blot (immunoblot). In addition, antiserum was analyzed for its molecular specificity by a pepscan as well as its in vitro neutra lizing ability. In general, results obtained with antisera to the pept ides paralleled the results obtained with the antisera to the KLH-conj ugated peptides except that the titers or strength of reaction in the assays was less. Antisera to the VDs in both strains of mice gave ELIS A titers to the homologous VD peptide ranging from 1,000 to >64,000. T he strength of reactivity with the reduced MOMP as judged by Western b lot, in most cases, paralleled the ELISA titer to the peptide. However , only antisera raised in both strains of mice to the VD1 and VD4 pept ides reacted strongly with the EBs, suggesting surface exposure of the se VDs. In addition, antisera to VD3 from C57BL/6 mice gave strong rea ctivity to EBs. By pepscan analysis antisera from both strains of mice reacted with several VD1 and VD3 octameric peptides, with weaker reac tivity being seen with the octameric peptides in the other two VDs. Th is was in contrast to antisera raised to EBs of C. pneumoniae TW-183, which identified two immunogenic regions, one in VD1 and the other map ped to VD4. While antisera raised to EBs strongly neutralized the infe ctivity of C. pneumoniae, none of the peptide antisera was able to neu tralize. In addition, peptides to the VDs were not able to block the n eutralizing ability of the antisera to EBs of C. pneumoniae. Therefore , these results suggest that the VDs of the MOMP of C. pneumoniae are surface exposed but do not elicit neutralizing antibodies when linear peptides representing them are used as the immunogen.