Ia antigen expression and antigen-presenting function by macrophages isolated from hypersensitivity granulomas.

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Abstract
Macrophages were isolated from granulomas elicited in the liver by the eggs of the trematode Schistosoma mansoni. They were analyzed for the expression of determinants encoded by the I-A subregion of the major histocompatibility complex and for their ability to present antigen in a T cell proliferation assay. Seventy-five to 81% of the macrophages were found to bear I-A antigens after 24 hr in culture; they also were shown to be effective in carrying out antigen-presenting function. Subsequent in vitro cultivation for up to 4 days demonstrated a progressive loss of I-A molecules, which correlated with a corresponding reduction in antigen-presenting capability. The latter was antigen-specific, blocked by monoclonal antibody directed against I-A, and abrogated after depletion of I-A-positive macrophages. Populations of macrophages from hepatic egg granulomas were richer in I-A-positive cells, and were more effective in terms of antigen-presenting capability compared to those obtained from foreign body-type granulomas. These observations suggest a central role for macrophages from infectious granulomas in the induction and maintenance of immunity and hypersensitivity.