Protective activity of a murine monoclonal antibody against acute and chronic experimental infection with type IV group B streptococcus

A murine IgM monoclonal antibody (MAb H11) was developed against the type polysaccharide capsular antigen of group B streptococcus (GBS), serotype IV, after intraperitoneal immunisation of BALB/c mice with heat-killed bacteria. MAb H11 reacted in immunodiffusion with the purified polysaccharide in both its sialylated and desialylated form, giving a line of identity, and opsonised type IV GBS strains in an in vitro assay. When administered at the time of intraperitoneal lethal challenge with homologous GBS, or 4 h earlier, MAb H11 protected 90% of the mice. Protection was still observed when MAb H11 was given 4 h after the challenge. This MAb was strongly effective in preventing septic arthritis induced by type IV GBS.