A family of strain-variant surface lipoproteins of Mycoplasma fermentans

Abstract

The wall-less procaryote Mycoplasma fermentans is currently being examined as an agent potentially associated with human disease, including infectious processes affecting immunocompromised individuals. To delineate and understand the interactions of M. fermentans with its host, specific membrane surface components were characterized as markers for detecting the organism and for assessing heterogeneity in antigenic surface architecture within this mycoplasma species. Detergent phase fractionation of metabolically labeled organisms of type strain PG18 identified a family of prominent integral membrane proteins; several of these labeled with 35S-cysteine and 3H-palmitate, which are characteristics of procaryotic lipoproteins. Specific monoclonal and polyclonal antibodies raised to strain PG18 components further distinguished seven of these membrane proteins, which were localized on the organism's surface by monitoring their selective susceptibility during trypsin treatment of intact cells. With these antibodies, Western immunoblot profiles of surface membrane antigens expressed on strain PG18 were compared with those expressed on the recently identified Incognitus strain of M. fermentans, as well as with several other human and animal mycoplasma species. While the antibodies were specific for M. fermentans, marked differences were observed between the strains in the size of one surface lipoprotein and in the apparent levels of several antigens expressed in the cultured populations analyzed. Some monoclonal antibodies to strain PG18 and a previously described monoclonal antibody to strain Incognitus showed apparent selectivity for the strain used for immunization. Monoclonal antibodies developed here recognize stable epitopes defining a family of surface lipoproteins and provide critical tools to determine the basis of surface variation in this mycoplasma species and to assess the location and antigenic phenotypes of organisms in the human host.