Serum antibodies in rickettsia patients as determined by immunoblotting technique

The Western-blot technique (WB) was used to determine which polypeptides of Israeli spotted fever (ISF) isolates and other spotted fever group rickettssia (SFGR) reference isolates (G212, S484, A828) and two reference strains. R. Rickettsii (Sheila Smith strain) and R. conorii (Boutonneuse fever), were used as antigen sources for the WB. Immunoperoxidase assay (IPA) seropositive (titer greater than 80) and seronegative (titer less than) sera were examined with the separated polypeptides of the above strains. WB analysis of the rickettsial polypeptide-serum reactions showed that R. conorii and the three isolates of ISF reacted identically with the sera, except that in the three ISF strains a 175 kD protein was present. It was also observed that all of the IPA seropositive sera examined reacted with the following polypeptides: 18kD, 20kD, 22kD (28kD to 37 kD LPS group), while each seropositive and seronegative serum reacted differently with polypeptides 23kD, 42kD, 45kD, 46kD, 52kD, 55kD, 70kD, 82kD, 105kD, 125kD, 155kD and 175kD. Using this technique, no heat labile polypeptides (preelectrophoretic treatment: 100 degrees C for 2 min vs 37 degrees C for 20 min) were observed in SFGR strains used in this study. Our results indicate that the immunoblot technique shows no difference between R. conorii and ISF antigens except the existence of 175kD protein antigen in the latter.