Peripheral blood mononuclear cells (PBMC) from 80 normal donors were studied for their capacity to proliferate in response to Pan T2, an IgG1 monoclonal antibody (MoAb), that recognizes the CD3 complex. Forty percent of this population, regardless of sex or age, were found to be non-responders. However, the binding of MoAb Pan T2 to T cells as studied by indirect immunofluorescence was positive in all the donors. The addition of IL 1 or IL 2 to Pan T2-stimulated non-responder lymphocytes did not activate T cell proliferation, while the addition of responder monocytes restored the proliferation capacity in non-responder PBMC. The data indicate the existence of a heterogeneous responsiveness among normal individuals to a mitogenic IgG1 MoAb, and are in agreement with reports obtained using other anti-T3 MoAbs of IgG1 isotype, i.e. UCHT1, Leu4 and WT31. This defect is reported to be a function of monocytes, related to a polymorphism of Fc receptors for mouse IgG1 on human monocytic cells.
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