THE LPS LOCALIZATION MIGHT EXPLAIN THE LACK OF PROTECTION OF LPS-SPECIFIC ANTIBODIES IN ABORTION-CAUSING CHLAMYDIA-PSITTACI INFECTIONS

Four monoclonal antibodies against chlamydial lipopolysaccharide (LPS) were used to study their localization and distribution in the Chlamyd ia psittaci AB7 abortion-causing strain by immunoelectron microscopy. A non-embedding technique on whole chlamydiae, together with a post-em bedding technique on McCoy cells infected with the strain, were perfor med. lmmunogold labelling was observed on the surface of reticular bod ies (RB), but not on elementary bodies (EB). Immunolabelling was obser ved in ultrathin sections on both sides of the external chlamydial mem brane, mainly on the inner side of EB and on the outer side of RB. Imm unogold density was higher in EB than in RB; however, the absolute num ber of gold particles was higher in RB than EB, suggesting a loss of i mmunolabelling during the transformation of RB into EB. Specific label ling of LPS was also found in electrodense and adielectronic vacuoles near the surface of the cytoplasmic membrane of infected McCoy cells. These results suggest that the lack of protection against some chlamyd ial strains, despite the presence of anti-LPS specific antibodies, is due to the localization of LPS on the inner side of the external membr ane of EB.