Accessory function of thymic and tonsillar dendritic cells in interferon gamma production by T lymphocytes

Human dendritic cells (DC) were purified from tonsils and thymus by a three-step procedure. Over 85% of cells in the purified DC preparations were identified as DC based on their characteristic morphology, presence of HLA-DR, Pro-Iml and Pro-Im2 antigens, and absence of macrophage associated antigens OKM1 and OKM5. To study the accessory function of DC in IFN-gamma production, T lymphocytes and T4+ or T8+ subsets were purified from peripheral blood and tonsils. Addition of autologous or allogeneic tonsillar DC to cultures of purified T cells caused up to a fifteen-fold increase in phytohemagglutinin (PHA)-induced IFN-gamma production and up to a seven-fold augmentation of IFN-gamma induction by interleukin 2 (IL 2). Thymic DC also showed a similar potent accessory activity on IFN-gamma production with concanavalin A (Con A) or PHA. Marked enhancement of IFN-gamma production by T cells was seen in the presence of as little as 0.3% thymic DC.