Human polysaccharide-specific B cells are responsive to pokeweed mitogen and IL-6

The responsiveness of polysaccharide-specific B cells to PWM was examined in vitro. Spleen cells from six patients immunized with Haemophilus influenzae type b-diphtheria toxoid, pneumococcal and meningococcal vaccines were T cell-depleted and separated by Percoll density gradient centrifugation. In each B cell fraction, spontaneous antibody production was demonstrated to capsular polysaccharides as well as diphtheria toxoid. The peak of spontaneous antibody production was demonstrated to be five to seven days after immunization. When T cells and PWM were added, the total Ig secretion increased in all B cell fractions. PWM also enhanced IgG antibody directed to each of three polysaccharide Ag measured. This enhancement was most noticeable for nonresting B cells. The PWM effect was not confined to IgG, as IgM and IgA to Neisseria meningitidis type C were measured and also enhanced. The kinetics of the PWM response demonstrated the most IgG antibody to polysaccharide Ag from spleens immunized five to seven days before splenectomy. When the patients were immunized either 2 days or 4 mo before splenectomy, no spontaneous IgG antibody to polysaccharides was detected although PWM induced small amounts of antibody. Finally, anti-IL-6 antibody blocked PWM-induced total and polysaccharide-specific antibody production. We conclude that human polysaccharide-specific B cells are responsive to PWM and IL-6. We suggest that polysaccharide B cells are not truly "T cell-independent" and may respond to T cell lymphokines and thus are similar to protein-specific B cells.