IDENTIFICATION OF AFIPIA-FELIS ANTIGENS IN CULTURE-MEDIUM - REACTION WITH HUMAN SERA

Fourteen protein antigens were identified on SDS-PAGE of Afipia felis culture supernatant. Immunoblotting against 10 monoclonal antibodies o btained from mice infected with live A. felis showed that 4 antibodies reacted with a 56 kDa band and 3 with both 56 kDa and 62 kDa bands. C ompared with A, felis sonicate, the reacting proteins in culture super natant showed an increase in molecular mass of 2-3 kDa, suggesting tha t they were more glycosylated. Purified antigen obtained by affinity c hromatography of culture supernatant on the seven immobilized antibodi es was tested against antibodies reacting with the 56 kDa and 62 kDa b ands. All eluates contained both components, suggesting that the antib odies were directed against different epitopes of a double antigen hel d together during the affinity chromatography but cleaved by reduction and SDS-PAGE. The molecular size of the uncleaved protein in culture supernatant was determined by size-exclusion chromatography as >1000 k Da. Testing of pre- and post-infection rabbit sera in immunoblotting a gainst culture supernatant demonstrated that the 56 kDa and 62 kDa com ponents gave the most prominent specific reactions with post-infection sera. One of fifty human sera submitted for resting for cat-scratch d isease and 1 of 50 sera from healthy blood donors reacted with several bands in A. felis culture supernatant, including the 56 kDa and 62 kD a bands.