ANTIGEN-BINDING B-CELLS AND POLYREACTIVE ANTIBODIES

The present experiments were initiated to see if cells capable of binding antigens could make polyreactive antibodies. Fluorescein isothiocyanate-labeled self and non-self antigens were incubated with B cells from normal individuals. Antigen-binding cells were separated from non-antigen-binding cells by flow cytometry, immortalized with Epstein-Ban virus and analyzed at the clonal level for their capacity to make polyreactive antibodies. Four to six times more cells making polyreactive antibodies were found in the B cell subset that bound antigens than in the B cell subset that did not bind antigens. The majority of the polyreactive antibodies were of the immunoglobulin (Ig)M isotype. Immunoflow cytometry revealed that cell lines making polyreactive antibodies bound a variety of antigens (e.g., insulin, IgGFc and beta-galactosidase), whereas cell lines making monoreactive antibodies bound only a single antigen. The binding of antigens to B cell lines that made polyreactive antibodies could be inhibited (range, 28 %-57 %) by both homogeneous and heterogeneous antigens. Both CD5(+) and CD5(-) antigen-binding B cells made polyreactive antibodies, but the frequency was slightly higher in the CD5(+) antigen-binding (85 %) as compared to the CD5(-) antigen-binding (50 %) population. Comparison of CD5(+) B cells that bound antigens with CD5(+) B cells that did not bind antigens showed that approximately 86 % of the former, but only 15 % of the latter, made polyreactive antibodies. It is concluded that cells capable of binding a variety of different antigens can make polyreactive antibodies and that antigen binding is a good marker for identifying polyreactive antibody-producing cells.