MONOCLONAL-ANTIBODY TO A CONSERVED EPITOPE ON PROTEINS ENCODED BY BABESIA-BIGEMINA AND PRESENT ON THE SURFACE OF INTACT INFECTED ERYTHROCYTES

To define Babesia bigemina-specific antigens on the surface of infecte d erythrocytes, monoclonal antibodies (MAbs) were identified by live-c ell immunofluorescence. As determined by live-cell immunofluorescence, two MAbs made to the Mexico strain reacted with the Mexico strain and three Kenya strains, while three MAbs made to the Kenya-Ngong strain reacted with the Kenya strains but not the Mexico strain. Binding of M Ab 44.18 (made to the Mexico strain) to a strain-common epitope was co nfirmed by immunoelectron microscopy and by surface-specific immunopre cipitation of [S-35]methionine-labeled proteins (200, 28, and 16 kDa i n size), which also demonstrated that the MAb recognized an epitope on proteins encoded by B, bigemina, In immunoblots, the MAb bound to pre dominant antigens with sizes of 200 and 220 kDa in erythrocyte lysates infected with strains from Puerto Rico, St, Croix, Texcoco (Mexico), Kenya, and Mexico, Major antigens with sizes of 200 and 220 kDa were i solated from a MAb 44.18 affinity matrix. Calf serum antibodies to the se isolated antigens bound to erythrocytes infected with either the Me xico or Kenya strains as determined by live cell immunofluorescence, a llowing the conclusion that at least one conserved surface epitope was recognized, Calf serum antibodies identified major labeled proteins w ith sizes of 200 and 72 kDa by surface-specific immunoprecipitation, a nd infected erythrocytes sensitized with these antibodies were phagocy tized by cultured bovine peripheral blood monocytes. These results pro vide a rationale for evaluating antigens identified by MAb 44.18 indiv idually and as components of subunit vaccines.