Recombinant interleukin-4 promotes expression of the CD25 (Tac) antigen at the plasma membrane of high-density human tonsillar B lymphocytes.

High-density human B lymphocytes were prepared from tonsillar mononuclear cells by depletion of adherent cells and T lymphocytes, followed by discontinuous density gradient centrifugation. The B cells were analysed for the levels of expression of the CD25 (Tac) antigen marker by flow cytometry following culture with a variety of cytokines. IL-4 could induce elevated levels of CD25 on high-density, putatively resting B lymphocytes in a dose-dependent fashion. Expression of CD25 at the B-cell surface could not be promoted by interleukin-2 (IL-2), interferon-gamma (IFN-gamma) or by a crude preparation of B-cell growth factor 2 (BCGF-2). Mitogenic challenge of the B cells with pokeweed mitogen (PWM) and a combination of phorbol ester and calcium ionophore were similarly ineffective, although a small increase in CD25 expression could be detected when the B cells were cultured with phytohaemagglutinin A (PHA). The ability of IL-4 to promote CD25 expression was abolished by the presence of IFN-gamma in the culture. Titration experiments suggested that the amount of IL-4 required to produce a half-maximal increase in CD25 expression was approximately 40 U/ml; this is considerably greater than the 8-10 U/ml required to produce the equivalent effect on CD23 expression. The ability of IL-4 to promote CD25 expression in the high-density B-lymphocyte population was apparently independent of proliferation of the cells. IL-4 could not promote Tac expression on high-density T cells prepared from the same tissue source.