Characterization of Two Fc Receptors for Mouse Immunoglobulins on Human Monocytes and Cell Lines.

We have previously reported a polymorphism in the mitogenic effect of murine (m) IgGI anti-CD3 monoclonal antibodies. This polymorphism was genetically determined and could be attributed to polymorphism of the Fc receptor (FcR) for mIgGl present on human monocytes. We have now extended these studies by quantitating FcR expression on monocytes and cell lines by it recently developed EA rosette assay, using the erythrocyte-associated pseudoperoxidase activity. The data show that the polymorphism of the monocyte FcR for mIg2a-based on a quantitative rather than an absolute difference. Furthermore, this FcR is specific for mIgGI and does not bind mIgG2a nor mIgG2b nor surprisingly, human IgG. The expression of this FcR on cell lines correlates with their accessory function in IgG I anti-CD3-induced T cell proliferation mIgG2a can inhibit the rosetting of monocytes with erythrocytes sensitized with human IgG. The FcR detected by this rosette technique can interact with all four human IgG subclasses but not with mIgG1 or mIgG2b. The expression of this type of FcR in human cell lines correlates well with their ability to support mIgG2a anti-CD3-induced mitogenesis. These direct measurements of FcR expression support the concept that human monocytes have two independent FcR with affinity for mouse IgG: one receptor specific for mIgG2a (which also binds human IgG), and a second specific for mIgG1. [ABSTRACT FROM AUTHOR]