Carrier (KLH)-speciflc type 1 T cell clones (Th1), which are defined by secretion of IL-2 and IFN-γ but not IL-4, and type 2 (Th2) clones, which secrete IL-4, but not IL-2 or IFN-γ, have been isolated and analyzed for their ability to collaborate in providing help for B cells to secrete phosphorylcholine-specific IgM antibodies. The resulting antibody responses exhibited a characteristic pattern suggesting two distinct regulatory interactions among the Th1, Th2, and B cells. At low doses of antigen, Th1 cells enhanced the helper function of the Th2 cells, an effect due primarily to IL-2. At high doses of antigen, Th1 cells or IFN-γ inhibited Th2-dependent antibody responses. The inhibitory effect of Th1 or IFN-γ affected primarily the hapten-carrier-linked portion of the response. The overall effect was a modulation of the antigen dose-response curve for antibody production, eliminating the sharp increases in dose response mediated by isolated T cell clones. The data suggest that collaborative interactions of Th1 and Th2 cells in antibody production may have important physiological consequences.
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