Antigen Presentation to Th1 but Not Th2 Cells by Macrophages Results in Nitric Oxide Production and Inhibition of T Cell Proliferation: Interferon-γ Is Essential but Insufficient

The induction and role of nitric oxide (NO) during antigen presentation by macrophages to T helper (Th) cell subsets was examined. When cultured with Th1 clones, macrophage APC produced NO only in the presence of cognate Ag, which in turn suppressed T cell proliferation. IFN-γ production by the activated Th1 cells was essential for the induction of NO. Th2 cells presented with the same cognate Ag did not induce NO production and proliferated uninhibited. Coactivation of Th1 and Th2 cells specific for the same Ag indicated that Th2 cells did not inhibit NO production, but were sensitive to NO induced by stimulated Th1 cells. Antigenic activation of Th2 cells in the presence of rIFN-γ resulted in NO-mediated inhibition of proliferation. Th2 cells provided only a cell-associated cofactor, whereas Th1 cells secreted a soluble cofactor for IFN-γ as well, i.e., TNF-α. Finally, a role for IFN-γ and NO during immune responses was studied in spleen cells obtained from immunized IFN-γ−/− mice. NO production and subsequent inhibition of Ag-specific proliferation ex vivo was observed only after the addition of rIFN-γ. These studies suggest an IFN-γ-dependent regulatory role for NO during Ag-specific Th cell activation involving macrophages, with obvious implications for Th subset-dependent immune responses in general.