Cross-neutralization of staphylococcal and streptococcal pyrogenic toxins by monoclonal and polyclonal antibodies

We evaluated cross-reactivity of antibodies against staphylococcal and streptococcal pyrogenic toxins. Monoclonal antibodies against staphylococcal enterotoxin (ET) C1 and streptococcal pyrogenic exotoxin (SPE) A were tested for reactivity with homologous and heterologous pyrogenic toxins in vitro. Ten immunoglobulin G1 anti-ET C1 monoclonal antibodies showed little or no cross-reactivity in an enzyme-linked immunosorbent assay, but many of these could neutralize the mitogenic effect of ET B, SPE A, or both. Two immunoglobulin M anti-ET C1 monoclonal antibodies and eight immunoglobulin M anti-SPE A monoclonal antibodies showed extensive cross-reactivity in the enzyme-linked immunosorbent assay and the mitogenicity neutralization assay. No cross-reactivity was observed with SPE C or toxic shock syndrome toxin 1. Rabbits immunized against ET B, ET C1, or SPE A were resistant to challenge with the immunizing toxin. In addition, reciprocal immunity was stimulated by the two ETs, and immunity to SPE A provided protection against ET B but not ET C1. These results show that staphylococcal and streptococcal pyrogenic toxins which share sequence homology have common antigenic determinants which may not be detected in Ouchterlony immunodiffusion assays.