Human interdigitating dendritic cells induce isotype switching and IL-13-dependent IgM production in CD40-activated naive B cells

Interdigitating dendritic cells (IDC) represent a mature progeny of dendrit ic cells (DC) in vivo and are exhibiting a strong lymphocyte stimulatory po tential. Because of the restricted localization to secondary lymphoid organ s where decisive cellular interactions take place in the initial events of immunity, IDC regulatory function was addressed in relation to naive B cell s. In this study, we demonstrate that human tonsillar IDC induce a dual res ponse from CD40-activated IgD(+)/CD38(-) naive B lymphocytes. IDC direct na ive B cells toward either isotype switching or an IL-13-dependent IgM secre tion. IDC-dependent proliferation, isotype switching, and Ig production are all strictly mediated by soluble factors, suggesting that such skewing in B cell activation is the result of differential cytokine expression. Moreov er, IDC-expressed IL-13 represents a novel source of a cytokine with recent ly established effects in Th2 induction as well as in immunological disorde rs resulting in allergic reactions.