[Role of B cell surface IgM in antigen presentation].

Previous studies showed that both resting and lipopolysaccharide activated B cells were very effective accessory cells and antigen presenting cells in T cell responding to mitogens and antigens. This paper discusses the role of B cell surface IgM in antigen presentation. Splenic B cells obtained from C57BL/6 mouse were depleted of macrophages, dendritic cells and T cells. The purified B cells were prepulsed with sheep anti-mouse IgM antibody (SaM) at 4 degrees C for 60 min or with tetanus toxoid antigen (TT-Ag) at 37 degrees C for 12 h before pulsing with TT-Ag or SaM. Then B cells (2 x 10(5)/well) were used as antigen presenting cells without further addition of TT-Ag in TT-Ag primed T cells (2 x 10(5)/well, obtained from TT-Ag immunized C57BL/6 mouse lymph node) proliferation. The results showed that antigen presentation of B cells prepulsed with SaM before pulsing with TT-Ag was blocked. But if B cells were preincubated with TT-Ag before pulsing with SaM, antigen presentation of B cells was not blocked by SaM. These results have suggested that B cell surface IgM can take up antigen and can present the antigen to antigen specific T cells. It has also been revealed that B cell surface IgM by taking up antigen plays an important role in antigen presentation. Also, the biological significance of the role on B cell surface IgM in antigen presentation is discussed.