VARIABLE EXPRESSION OF EPITOPES ON THE SURFACE OF MYCOPLASMA-GALLISEPTICUM DEMONSTRATED WITH MONOCLONAL-ANTIBODIES

Twelve monoclonal antibodies (Mabs) against Mycoplasma gallisepticum ( Mg) strains F, R, S6(208) and PET2 were used for analysis of epitopes of 22 Mg strains. Six Mabs recognized surface epitopes in the majority of strains, but did not react with variant strains like K 503 and K 7 03. Two Mabs reacted with epitopes on about 56 kilodalton (kDa) protei ns and showing consistent expression on Mg colonies. Three Mabs recogn ized three different variable surface epitopes associated with about 6 7 kDa proteins and one Mab variable epitope on about 33 and 80 kDa pro teins. Two-dimensional immunoblotting showed considerable differences in the charge of proteins bearing variable surface epitopes in differe nt Mg strains. Subcloning of four low passage Mg strains using Mabs fo r screening populations that derived from a single colony with defined surface epitopes showed that some colonies may switch surface epitope s associated with 67 and 80 kDa proteins. This switching was reversibl e and generated subpopulations of Mg expressing different combinations of surface epitopes. Phenotypic switching of epitopes probably occurs also in vivo and may be the mechanism enabling Mg to evade the host i mmune response.