Antigen-specific activation of effector macrophages by IFN-gamma producing (TH1) T cell clones. Failure of IL-4-producing (TH2) T cell clones to activate effector function in macrophages.

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Abstract
IFN-gamma-producing (TH1) and IL-4-producing (TH2) clones were assayed for their ability to directly induce cytostatic activity in macrophages generated from splenic myeloid precursors (M phi-c). In the presence, but not in the absence, of antigen, TH1 clones activated the M phi-c to inhibit the growth of P815 tumor cells in vitro. TH2 clones were not able to activate such effector activity in the M phi-c. The M phi-c did effectively present Ag to the TH2 clones as evidenced by the proliferation of TH2 cells cultured with Ag in the presence, but not in the absence, of M phi-c. Therefore, although both TH1 and TH2 were activated by cognate interaction with antigen presenting M phi-c, only TH1:M phi-c interactions displayed reciprocity resulting in activation of the M phi-c. TH1-derived lymphokines or rIFN-gamma, in the presence of LPS, could activate proteose-peptone elicited M phi, resident peritoneal M phi, and M phi-c whereas neither TH2-derived lymphokines nor rIL4 could induce detectable activity in any of the 3 M phi populations. IFN-gamma, in the absence of LPS, could activate the elicited M phi and to a lesser and more variable degree, the resident M phi Only the M phi-c consistently required both IFN-gamma and LPS for induction of cytostatic activity. Since M phi-c consistently required at least two signals for activation, the ability of TH1-derived lymphokines to synergize with TH2 cells in M phi activation was examined. TH2 could activate the Ag-presenting M phi-c in the presence of IFN-gamma. The ability of added IFN-gamma to synergize with TH2 indicates that the cognate interaction between TH2 and antigen presenting M phi-c does result in delivery of at least one of the signal required for M phi activation.