HUMAN INTERDIGITATING DENDRITIC CELLS DIRECTLY STIMULATE CD40-ACTIVATED NAIVE B-CELLS

Human interdigitating dendritic cells (IDC) were isolated from tonsils based on their CD40(+) lineage-negative expression in situ. Isolated IDC displayed a phenotypic profile similar to that of IDC in tonsils a nd spleen in situ, characterized by high-level expression of major his tocompatibility complex class II, the costimulatory molecules B7.1 (CD 80) and B7.2 (CD86), expression of the late DC maturation marker CD83, and no expression of CD1a, CD13, or CD33. IDC also showed weak nonspe cific esterase staining and had the ability to induce an allogeneic mi xed lymphocyte reaction. In this study, we further show that in the pr esence of surrogate activated T cells in the form of CD40 ligation and IL-2, IDC enhance the proliferation of naive B cells and induce their differentiation into plasma cells producing IgM. Evidence for the ana tomical co-localization of naive B cells and IDC in the T cell area to gether with the data obtained in vitro implies a role for IDC in the i nitiation of the extrafollicular reaction.