Using a monoclonal anti-human Fc epsilon R antibody (H107), we found that lymphocytosis promoting factor (LPF), phytohaemagglutinin (PHA-P) and Concanavalin A (Con A) could induce Fc epsilon R, detected by immunofluorescence study, on normal human peripheral blood lymphocytes without IgE. The number of Fc epsilon R bearing lymphocytes was increased by stimulation with 3, 10 and 10 micrograms/ml of LPF, PHA-P and Con A, respectively, from 6.0 +/- 3.0/1000 cells to 26.0 +/- 7.9, 54.0 +/- 6.7 and 24.8 +/- 7.1/1000 cells, respectively. Although the induction of Fc epsilon R occurred neither in the separated T-enriched fraction (TEF) nor the T-depleted fraction (TDF), it recovered when the two fractions were mixed. The cell free supernatants from TEF stimulated with LPF or PHA-P could increase Fc epsilon R(+) cells in TDF, whereas those from TDF failed to increase them in TEF. The results suggest that the induction of Fc epsilon R occurs mainly on B lymphocytes by the soluble factor(s) formed by T cells stimulated with LPF or PHA-P. The induction of Fc epsilon R by stimulants was completely inhibited by 10(-6) M dexamethasone. It was demonstrated that the effects of dexamethasone on lymphocytes were dual: one was on B cells to inhibit responsive increases of Fc epsilon R, and the other was on T cells to suppress the formation of the soluble factor(s) which induced Fc epsilon R on B cells
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