Characterization of the murine macrophage receptor for group B streptococci

Attachment of group B streptococci to macrophages is mediated by a 21-kDa protein

Group B Streptococcus (GBS) is able to bind to human macrophages in vitro in the absence of exogenous opsonins. The exact mechanisms that mediate this attachment are unclear. This study was undertaken to determine what protein adhesins are present on the surface of GBS that mediate attachment to macrophages. We have identified a 21-kDa protein from the envelope of GBS type III that directly binds to macrophages as determined by Western blot analysis. Antiserum against this protein was able to inhibit binding of GBS to macrophages by greater than 80% as measured by flow cytometry. Antiserum against the 21-kDa protein cross-reacted with 21-kDa proteins from GBS type Ib, type II, type III (COH31 and MR732) and type IV, as well as Staphyloccus epidermidis, but not GBS type Ia, Listeria monocytogenes or Enterococcus faecalis. This protein may be important in mediating the attachment of GBS to macrophages in an opsonin-poor environment.

Adherence of Salmonella typhimurium to murine peritoneal macrophages is mediated by lipopolysaccharide and complement receptors

Adherence of Salmonella typhimurium to mouse peritoneal macrophages (Mø) was monitored using a direct microscopic assay and flow cytometry. Competitive binding studies using wild-type lipopolysaccharide and derivatives confirmed a role for this moiety in bacterial adherence. Mø pretreated with 2-deoxy-D-glucose exhibited lower binding activity than did untreated controls, suggesting involvement of either Fc or complement receptors. Pre-exposing Mø to Fc fragments, however, failed to reduce bacterial binding, thus eliminating a role for Fc receptors in this process. Mø pretreated with neutrophil elastase exhibited a diminished ability to bind S. typhimurium, suggesting involvement of complement receptor 1. Monoclonal antibodies M1/70 and M18/2, specific for epitopes on the alpha and beta chains, respectively, of complement receptor 3, also blocked this adherence. In each case we were unable to eliminate completely bacterial adhesion to Mø. Monoclonal antibodies to two additional Mø receptors, Mac-2 and Mac-3, did not block bacterial attachment. These data indicate that multiple mechanisms are involved in the initial adhesion of S. typhimurium to mouse Mø.