title: Electron microscopic localization of receptors for aggregated beta 2-microglobulin on the surface of beta-hemolytic streptococci.
abstract: The presence and location of receptors for aggregated human beta 2-microglobulin (beta 2m) on the surface of group A, C, and G streptococci were studied by electron microscopic techniques. Ferritin-conjugated aggregates of human beta 2m were used in direct binding experiments. Ferritin-conjugated antibodies against beta 2m were employed in a two-step indirect binding assay where the streptococci were incubated with unlabeled beta 2m aggregates before the addition of antibodies. Similar results were obtained with these two methods. Among tested group C and G strains, some showed binding of beta 2m, whereas others were negative. In group A streptococci, beta 2m binding was localized to filamentous structures typical of M protein. In two M protein-negative group A strains, the reactivity was heterogeneous, revealing a majority of unlabeled, but also some heavily labeled streptococci. Morphologically, these beta 2m-binding bacteria exhibited M protein-like projections in contrast to the smooth surfaces of unlabeled cells.
mesh_terms: D002462:Cell Membrane / Q000032:analysis / Q000648:ultrastructure; D005293:Ferritins; D008854:Microscopy, Electron; D011971:Receptors, Immunologic / Q000032:analysis*; D013291:Streptococcus / Q000032:analysis* / Q000648:ultrastructure; D013297:Streptococcus pyogenes / Q000032:analysis* / Q000648:ultrastructure; D001613:beta 2-Microglobulin / Q000378:metabolism*
chemical_list: D011971:Receptors, Immunologic; C027292:beta 2 microglobulin receptor; D001613:beta 2-Microglobulin; D005293:Ferritins