Mouse-protective effect of rabbit anti-R-protein antibodies against group B streptococci type II carrying R-protein. Lack of effect on type III carrying R-protein.

R-proteins was isolated by affinity chromatography from an alkaline extract of group B streptococci, type III. the identity of the protein was demonstrated by pepsin- and trypsin-treatment and in double diffusion-in-gel with antisera from other laboratories. A monospecific rabbit antiserum against the R-protein was studied in mouse-protection tests, using three type II strains with R-protein and three without, and six type III strains, of which four carried R-protein. the serum protected animals from infection by type II strains carrying R-protein, but not against any of the other strains. The capacity of anti-R-protein serum to opsonize type II strains carrying R-protein was also demonstrated in phagocytosis experiments with mouse peritoneal macrophages. Studies with radio-labelled protein A and anti-R-protein antibodies showed that R-protein was localized on the surface of both type II and type III groups B streptococci. Taken together, the results suggest that type II group B streptococci should be divided into two subtypes, II, R+ and II, R-.