Marginal zone, but not follicular B cells, are potent activators of naive CD4 T cells

The early involvement of marginal zone (MZ) B lymphocytes in T-independent immune responses is well established. In this study we compared the abilities of MZ and follicular (FO) B cells to collaborate with T cells. After immunization with soluble hen egg lysozyme, both MZ and FO B cells captured Ag and migrated to T cell areas in the response to hen egg lysozyme. MZ B cells were far superior to FO B cells in inducing CD4(+) T cell expansion both in vitro and in vivo. MZ, but not FO, B cells, after interaction with T cells, differentiated into plasma cells, and in addition they stimulated Ag-specitic CD4(+) T cells to produce high levels of Th1-like cytokines upon primary stimulation in vitro. These results indicate that MZ B cells rapidly and effectively capture soluble Ag and activate CD4(+) T cells to become effector T cells. The enhanced capacity of MZ B cells to prime T cells in this study appeared to be intrinsic to MZ B cells, as both MZ and FO B cell populations express an identical Ag receptor. The Journal of Immunology, 2004, 172: 803-811.