Macrophage activation: dissociation of cytotoxic activity from Ia-A antigen expression.

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Abstract
Peritoneal macrophages were obtained from DBA/2 mice that were untreated or after the injection of BCG, thioglycollate broth, proteose-peptone broth or .gamma.-irradiated P-815 [mouse mastocytoma] tumor cells. These macrophages were activated to become cytotoxic for a [mouse] fibroblast cell line (L 929) by the addition of lymphokines (LK), lipopolysaccharide (LPS) or fibroblast interferon (IFN-.beta.) and the expression of I region-associated antigens (Ia-Ad) on the macrophages was examined both before and after activation. Thioglycollate-elicited macrophages became Ia-A+ when activated by LK, but they remained Ia-A- when activated by LPS or IFN-.beta.. Resident macrophages and proteose-peptone-elicited macrophages remained Ia-A- when activated with LK. Macrophages from BCG-infected mice were both Ia-A+ and cytotoxic for tumor cells without further treatment. Macrophages from mice injected with .gamma.-irradiated P-815 mastocytoma cells were Ia-A+ but not cytotoxic, and these macrophages could not be made cytotoxic by incubation with LK. The cultured macrophage-like [murine leukemia] cell lines P388DL and WEHI-3 became Ia-A+ after incubation with LK, and this treatment amplified the cytotoxicity of both cell lines. Apparently, a number of factors are important in determining whether Ia-A expression accompanies macrophage activation, and Ia-A is evidently irrelevant as a surface marker for macrophage activation.