Separate Ia-like determinants in human lymphocytes and macrophages.

Some human alloantisera cytotoxic for B-lymphocyte preparations lost their reactivity when the number of contaminating monocytes was decreased by treatment with carbonyl iron. Such sera were found to react with the corresponding monocyte preparations isolated by adherence to Petri dishes. Macrophage antibodies were present in 38% of random sera from multiparous women and in 70% of sera from kidney transplant recipients. They could not be absorbed with B-lymphocyte preparations, thus suggesting that determinants expressed in macrophages were not present in B lymphocytes. Macrophages stimulate in mixed lymphocyte culture and participate in immune reactions. It is possible that alloantigens of macrophages, as observed in the present experiments, are products of genes associated with these histocompatibility-controlled functions.