DEMONSTRATION OF HEAT-LABILE AND HEAT-STABLE EPITOPES OF RICKETTSIA-JAPONICA ON ULTRATHIN SECTIONS

BACKGROUND: Spotted fever group rickettsiae including Rickettsia japon ica have two major polypeptides and lipopolysaccharide (LPS)-like anti gen on the surface. The major part of the antibodies to these polypept ides generated by immunization with live rickettsiae are reactive with heat-labile and conformation-dependent epitopes. EXPERIMENTAL DESIGN: To demonstrate and precisely localize the heat-labile and heat-stable epitopes on the major surface polypeptides and LPS-like antigen of R. japonica, the immunocolloidal gold method was performed on ultrathin sections with polyclonal and monoclonal antibodies. The antigenicity a nd fine structure were preserved by using periodate-lysine-paraformald ehyde as fixative, followed by embedding with the resin Lowicryl K4M a t a polymerization temperature of -35 degrees C. RESULTS: Heat-labile and heat-stable epitopes on the two major surface polypeptides togethe r with LPS-like antigen of R. japonica were demonstrated at the same l ocation. These antigens were rather broadly distributed on the cell wa ll apart from the slime layer of the organism. The number of gold part icles corresponding to the LPS-like antigen was much larger than that corresponding to the polypeptide antigen. CONCLUSIONS: Heat-labile epi topes of rickettsiae could be preserved and demonstrated by using the procedure cited here. Moreover, the precise localization of the major surface polypeptides and LPS-like antigen could be achieved in the cel l wall by using ultrathin sections of infected cells instead of whole rickettsial cells. The LPS-like antigen was quantitatively predominant as judged by immunoelectron microscopy.