Monoclonal antibodies against human monocytes. II. Recognition of two distinct cell surface molecules

Three monoclonal antibodies (63D3, 63D2, and 61D3) with reactivity against human monocytes have been studied. They reacted with most adherent mononuclear cells but not with pure populations of peripheral blood B and T lymphocytes. Two of these antibodies, 63D3 and 63D2, competed in fluorescence inhibition experiments, recognized a monocyte surface antigen of about 200,000 daltons, and were idiotypically related. The third antibody, 61D3, did not compete with the others in fluorescence inhibition experiments, recognized a different surface molecule, and was idiotypically distinct from 63D3 and 63D2. Whereas 63D3 and 63D2 reacted very weakly with some granulocytes, 61D3 did not, suggesting that it is specific for monocytes alone.