Interferon-gamma- and interleukin-4-producing T cells can be primed on dendritic cells in vivo and do not require the presence of B cells.

The antigen-presenting cell (APC) requirements for the in vivo induction of Th1- and Th2-type responses were investigated using a severe combined immunodeficiency (SCID)mouse chimera model. SCID mice adoptively transferred with either T cells [SCID(T)] or T+B cells [SCID(T+B)] and immunized with antigen in adjuvant were able to generate antigen-specific T cells which could produce both interferon (IFN)-gamma and interleukin (IL)-4 upon in vitro restimulation. This suggests that B cell APC are not necessary for the priming of either IFN-gamma- or IL-4-producing T cells in vivo. The ability of different APC to activate Th2-dependent effector mechanisms was also investigated. SCID(T) and SCID(T + B) mice were infected with the nematode parasite Nippostrongylus brasiliensis and analyzed for the development of IL-5-dependent peripheral blood eosinophilia. Following infection both SCID(T) and SCID(T+B) mice generated similar numbers of peripheral blood eosinophils, suggesting that similar amounts of IL-5 had been produced. Therefore, B cell APC are also not required for the in vivo activation of Th2 cells to lymphokine production. To establish more precisely which APC prime T cells to produce IFN-gamma and IL-4, normal mice were immunized by injection of syngeneic splenic dendritic cells which had been pulsed with antigen in vitro. T cells from these immunized mice were able to produce good IFN-gamma and IL-4 responses upon in vitro restimulation with specific antigen; therefore, dendritic cells appear to be sufficient APC for the in vivo priming of both IFN-gamma- and IL-4-producing T cells.