Toward a role of dendritic cells in the germinal center reaction: Triggering of B cell proliferation and isotype switching

We have reported previously that in vitro generated dendritic cells (DC) ca n directly regulate B cell responses. Recently, germinal center DC (GCDC) w ere identified within B cell follicles, Due to their particular localizatio n, we have tested in the present study whether GCDC could contribute to key events characteristic of the GC reaction, Our present results demonstrate that 1) ex vivo GCDC induce a dramatic GC B cell expansion upon CD40 and IL -2 activation and drive plasma cell differentiation, 2) this property is sh ared by GCDC and blood DC, but not by Langerhans cells, 3) IL-12 production by GCDC is critical in GC B cell expansion and differentiation, and 4) imp ortantly, GCDC also induce IL-10-independent isotype switching toward IgG1, These observations support the novel concept that GCDC directly contribute to the germinal center reaction.