ADAPTIVE SURFACE-ANTIGEN VARIATION IN MYCOPLASMA-BOVIS TO THE HOST IMMUNE-RESPONSE

The variability of predominant Mycoplasma bovis surface antigens in th e presence of specific immune pressure was analyzed in an in vitro ass ay to determine if M. bovis could escape immune destruction. We have s hown that serum antibodies from immunized or experimentally infected c alves and monoclonal antibodies which specifically react with previous ly characterized or as yet undefined major M. bovis membrane surface p roteins cause repression of expression ol shortening of the target pro tein, or induce switching to expression of an antigenically distinct v ariant protein. We have further demonstrated that removal of the induc ing antibody results in reversion to the original phenotype. These res ults suggest that the level of expression and the length of M. bovis s urface antigens in the host is modulated by cognate antibodies. Accord ing to the surface antigenic variation systems, random selection of pr eexisting variants resistant to antibody-mediated inhibition or direct regulation of gene expression may be means by which this organism eva des host immune defences.