Comparison of the Fc Receptors for IgE on Human Lymphocytes and Monocytes

Fc receptors for IgE (Fc epsilon R) on human peripheral blood lymphocytes and monocytes and cultured lymphoblastoid and macrophage-like cell lines were compared with respect to: 1) binding affinity for radiolabeled IgE, 2) inhibition of IgE-specific rosette formation and inhibition of binding of radiolabeled IgE by an antiserum raised against Fc epsilon R isolated from a lymphoblastoid cell line, and 3) m.w. of radiolabeled cell surface proteins precipitated with the anti-Fc epsilon R serum. Scatchard analysis of 125I-IgE binding to lymphocytes, monocytes, and their corresponding cell lines showed biphasic binding curves with all cell types, from which 2 binding affinities were calculated to be KA = 6.2 +/- 1.1 and 2.0 +/- 0.5 x 10(7) M-1. The anti-Fc epsilon R serum inhibited both IgE rosette formation and binding of radiolabeled IgE by lymphocytes and monocytes but did not inhibit IgE rosettes formed by basophils. The inhibitory activity of the anti-Fc epsilon R serum could be absorbed with Fc epsilon R(+) but not with Fc epsilon R(-) cell lines. The anti-Fc epsilon R serum precipitated 2 peptides having m.w. of approximately 47,000 and 23,000 daltons from lysates of both cell surface-labeled lymphocyte and macrophage cell lines. These data indicate that Fc epsilon R on normal lymphocytes and monocytes, as well as on cultured lymphoblastoid and macrophage-like cells, are related structurally, since they share antigenic determinants, bind IgE with a similar affinity, and have similar m.w. However, they differ in all 3 parameters from Fc epsilon R on basophilic granulocytes.