Mouse protection assay for group B streptococcus type III.

The mucin model for group B Streptococcus (GBS) type III was used to assay the protective effect of sera against a type III challenge in mice. Hyperimmune rabbit sera, prepared by the Lancefield method against the laboratory reference strain (SS620) and a clinical isolate (M732), protected against a lethal challenge with either strain of GBS type III. Absorption of the sera with either of these type III strains removed the protective effect. Neither normal rabbit sera nor heterologous antisera (anti-Ia, SS615) provided protection; however, protection was obtained with pooled human gamma globulin. Sera from adult volunteers were tested to assay protective levels in the mouse model. Human sera enhanced the mouse lethality of the clinical isolate, M732, but not the laboratory reference strain, SS620. Sera from adults vaccinated with type III polysaccharide of GBS were also tested. The murine-mucin-GBS model may be developed as a screening test to measure protective antibody levels in the pre- and postvaccine treatment period. The model may also be used to measure protective antibody in pooled human gamma globulin for use in the passive immunization of high-risk individuals.