IgE receptors on human lymphocytes III. Expression of IgE receptors on mitogen‐stimulated human mononuclear cells

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Abstract
Human peripheral blood mononuclear cells (PBMC) were tested for the expression of Fee-receptor (FcεR) after stimulation with various mitogens in the absence of IgE. FcεR were found on virtually all the cells from 19 Epstein-Barr virus-transformed B cell lines including those derived from cord blood, from one agamma-globulinemic patient and VDS-0 pre-B cells. Hence, the data clearly indicate that FcεR may be expressed on very immature B cells. PBMC cultures stimulated with either pokeweed mitogen (PWM), phytohemagglutinin (PHA) or concanavalin A displayed an early increase of their content in FcεR-bearing cells followed by a decrease to levels below those of the control cultures. After fractionation of the PWM-stimulated cultures into T and B cell-enriched preparations, most of the FcεR+ cells were in the B cell fractions and the same low levels of FceR+ cells were found in the T cell fractions isolated from the PWM-stimulated and from the control cultures. Double-labeling experiments, employing biotinylated F(ab')2 monoclonal antibody to FcR and either fluorescein isothiocyanate-conjugated B1 or Mo2 monoclonal antibodies, indicated that PWM mainly exerted its effect on B cells and on monocytes. This effect was T cell dependent and it was mediated by soluble factors of T cell origin. At the peak of the PHA or concanavalin A response, most of the FceR-bearing cells were found in the B cell fraction but the T cells isolated from mitogen-stimulated cultures contained significantly more FcεR+ cells than those from the control cultures, suggesting that T cell mitogens had increased the expression of FcεR on some T cells. This view was supported by the finding of a higher proportion of FceR+ cells in PHA-stimulated than in control cultures of highly purified T cells with a maximum response at the end of the culture period. Double-labeling experiments at the peak (day 2) of the peripheral blood mononuclear cell response indicated that the expression of FcεR was increased on B cells (Bl+) and on monocytes (Mo2+). By using the same approach at the peak of the T cell response (day 7), it was found that T cells isolated from PHA-stimulated cultures expressed more FcεR than those isolated from control cultures. Moreover, in unstimulated cultures, FcεR was mainly expressed on T helper cells (Leu 3+) whereas in PHA-stimulated cultures FcεR was expressed on both T helper and T suppressor/cytotoxic cells (Leu 2+).

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