IMMUNE-RESPONSES TO THE R4 PROTEIN ANTIGEN OF GROUP-B STREPTOCOCCI AND ITS RELATIONSHIP TO OTHER STREPTOCOCCAL R4 PROTEINS

The R antigen, a trypsin-resistant protein observed in group A, C, F, G, and L streptococci, has also been found in group B streptococci (GB S). Although four species of the TC antigen have been described for GB S, the R4 protein is the most prevalent in GBS isolates recovered from humans. This study examined the prevalence of antibodies against the R4 antigen by Western blot (immunoblot) (WB) in sera from 40 mothers c olonized with GBS serotype II or III and from 26 noncolonized mothers; 92.5% of the colonized mothers had anti-R3 antibodies, compared with 54% of the noncolonized mothers (P < 0.001). Findings of antibodies in neonatal cord sera (n = 14) were concordant with maternal results by WB analysis for 71% of mother-infant pairs colonized with serotype II and for 57% of pairs colonized with serotype III. Of mothers known to be colonized with type II/R4 or III/R4, 100% (n = 12) had antibody aga inst R4 by WB. This study also evaluated the prevalence of antibody to the GBS R4 antigen in 48 sera from individuals with high and low grou p A streptococcal anti-DNase B titers. Of those individuals with an an ti-DNase B titer of >640, 64% had a positive WB for anti-R4 antibody, compared with 30% of individuals with low anti-DNase B titers (P < 0.0 5). The R4 antigen of GBS had immunologic identity to the R4 antigen o f group A streptococci. Overall, the findings suggested that antibodie s to the streptococcal R4 antigen were commonly present in GBS-coloniz ed mothers and that transplacental passage of these antibodies occurre d. The presence of antibody to R4 in non-GBS-colonized individuals may be due to immunologic responses to past exposure to the R antigen pre sent in GBS or other streptococcal groups.