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

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.