IMMUNOELECTRON MICROSCOPIC LOCALIZATION OF VARIABLE PROTEINS ON THE SURFACE OF MYCOPLASMA-BOVIS

The ultrastructural distribution and immunological accessibility of th e variable surface proteins VspA, VspB, VspC and VspD were determined by immunoelectron microscopy on the surface of negatively stained cell s of Mycoplasma bovis PG45 and 18 subclones, expressing either one or two of the Vsps. The variable proteins VspA, VspB, VspC and VspD, reco gnized by two monoclonal antibodies (mAb 1E5 and mAb 87-2) and visuali zed by goat-antimurine-IgM labelled with gold particles, showed identi cal distribution patterns on the surfaces of the cells of all M. bovis clones investigated. Cold particles were distributed over the whole c ell surface, arranged in clusters. The cell form seemed not to have an influence on the decoration pattern. Gold particles were also observe d in irregular distributions around the cells. All clones showed unlab elled cells as well as strongly and weakly labelled cells, There were in general, however, no significant differences in the percentages of unlabelled, weakly labelled and strongly labelled cells, either betwee n clones expressing different Vsps or between individual clones. No co rrelations were found between the numbers of labelled cells in immunoe lectron microscopy and the numbers of labelled colonies in immunobindi ng assay (IBA) originating from the same broth cultures. The percentag e of positive colonies in IBA was generally much higher than the perce ntage of positive cells in immunoelectron microscopy. The results show that the cells of the M. bovis clones are not identical, but differ i n their surface antigens, and reveal the high variable potential of th is species.