Figure 2. A schematic model shows our current understanding of the positive roles of B lymphocytes in tumor immunity.

a. Allogeneic B cells secrete IgG antibodies to recognize surface molecules on tumor cells, activate DCs, and induce the cell-killing activity of CD8⁺ T cells. b. B cells function as APCs for CD4⁺ and CD8⁺ T cells. c. B cells could express the death-inducing molecule FasL, and kill tumor cells through Fas-FasL connections. d. B cells could secrete granzyme B, to cause caspase3 activation and tumor cell apoptosis. Consequently, B lymphocytes perform positive functions in the regulation of many processes associated with tumor immunity.