Phosphorylcholine on Streptococcus pneumoniae R36a is responsible for in vitro polyclonal antibody secretion by human peripheral blood lymphocytes.

We have shown that Pc on the C-polysaccharide of Streptococcus pneumoniae R36a is responsible for polyclonal PFC responses induced in vitro by this bacterium in humans. R36a grown in media containing EA instead of CL, and therefore having phosphorylethanolamine instead of Pc in their C-polysaccharide, were unable to induce substantial PFC responses. When EA-substituted bacteria were chemically conjugated with Pc, their ability to induce polyclonal PFC was restored. Specific removal of Pc from the surface of the bacteria by the use PLC also resulted in abrogation of the polyclonal antibody response. These data are consistent with our hypothesis that polyclonal activation resulting from R36a stimulation may be mediated by a recently described Pc-binding receptor that is distributed on the surface of a subpopulation of B lymphocytes in humans and mice.