Isolation of follicular dendritic cells from human tonsils and adenoids. V. Effect on lymphocyte proliferation and differentiation.

Follicular dendritic cells (FDC) are located only in lymph follicles and are characterized by their capacity to retain high amounts of immune complexes on their plasma membranes. As their functions in germinal centres are unknown, we isolated them from human tonsils and cultured them with autologous lymphoid cells. Cultures of lymphoid cells alone or with added macrophages were used as controls. Lymphoid cells incorporated tritiated thymidine only when FDC and lectins were added; this could be shown after several periods of time. However, the Ig secretion by lymphoid cell populations was inhibited by FDC after several days in vitro. In contrast, the supernatants of lymphocytes cultured alone or with macrophages only for the same periods of time contained increasing amounts of immunoglobulins. This inhibitory effect of FDC on immunoglobulin production was observed for all considered isotypes. Our data suggest that FDC stimulate lymphoid cell proliferation but reduce B-cell differentiation. This is the first accessory cell activity definitely shown for FDC in cultures.