Induction of CD25 expression in human B lymphocytes by pharmacological activators of cellular signalling pathways

IL-4 promotes simultaneous expression of both the CD23 and CD25 antigens in resting human B lymphocytes in a dose-dependent manner. Simultaneous three-colour flow cytometric analysis revealed that CD19+/CD23+/CD25+ triple-positive cells were derived from a CD19+/CD23-/CD25- pool, and that induction of CD23 required lower doses of IL-4 than did induction of CD25. Although the concentrations of IL-4 required for half-maximal up-regulation of CD23 (35 pM) and CD25 (150 pM) expression were different, the capacity of IL-4 to promote expression of the two markers could be mimicked by the same combination of pharmacological agents. Thus, maximal expression of CD23 and CD25 was obtained with a 30 (or 120) second pulse with phorbol ester and/or ionomycin followed by a sustained (20 minute) treatment with forskolin. Use of BAPTA to chelate intracellular calcium suggested that IL-4 driven CD25 expression required mobilization of intracellular Ca2+. Finally, down-regulation of cellular protein kinase C by chronic treatment of resting B lymphocytes with phorbol ester abolished the ability of IL-4 to elevate CD23 and CD25 expression; phorbol ester treatment similarly abrogated the ability of anti-CD40 and anti-Ig reagents to promote expression of CD25. The data are consistent with the proposal that IL-4 influences CD23 and CD25 expression via a similar signal transduction pathway which involves both protein kinase C activation and elevation of intracellular cAMP levels.