In vivo polyclonal stimulation of antibody secretion by two types of bacteria.

We previously proposed that one benefit of early polyclonal antibody secretion after bacterial infection might be the formation of antibodies protective against infection by a second pathogen. In order to analyse this possibility, the polyclonal and anti-phosphorylcholine (PC) plaque-forming cell (PFC) response induced by Staphylococcus aureus Cowan I (SA) was compared with the same responses stimulated by unencapsulated Streptococcus pneumonia strain R36a. S. aureus stimulated significant anti-PC PFCs, despite an inability to detect immunoassay-reactive PC on the surface of SA (present on R36a). The induction of these antibodies appeared very similar to the mechanism for producing polyclonal responses. R36a also stimulated both anti-PC and polyclonal PFCs, but by different means. In summary, our data suggest that each type of bacteria induces polyclonal and anti-PC responses through different mechanisms, and that the polyclonal antibody response stimulated by one group of bacteria can contain antibodies directed towards a second and different genus of bacteria.