INTERACTION BETWEEN INTERLEUKIN-10 AND INTERLEUKIN-6 AND HUMAN B-CELLDIFFERENTIATION

Contrary to their opposing action on human T-lymphocytes and monocytes , both Interleukin (IL-)10 and IL-6 are potent differentiation factors of human B-cells. Both are known to induce immunoglobulin (Ig) produc tion. The precise mechanism of this converging effect of IL-6 and IL-1 0 remains elusive, however. Here we investigated the role of IL-6 in t he IL-IO dependent B-cell differentiation into Ia secreting cells. We found that co-stimulation of SAG-stimulated human peripheral B-lymphoc ytes with IL-10 and IL-6 exhibited no additive effect on Ig production over stimulation with IL-10 alone, and that IL-6 receptor blockade on ly mildly inhibited IL-10 induced Ig synthesis. In fact, we could show that stimulation of B-cells with IL-10 somewhat suppressed SAC induce d autocrine IL-6 production. Despite this suppression IL-6 levels rema ined sufficiently high to stimulate its receptor, and IL-6 binding to the B-cell surface was not affected. The failure of IL-6 to exert an a dditional effect on SAC+IL-10 induced Ig production suggests that IL-1 0 may recruit components of the IL-6 intracellular pathway for Ig indu ction. In conclusion we could demonstrate that IL-10 acts on B-cell di fferentiation independently of autocrine IL-6 and that it had a consid erably mild effect on B lymphocytic autocrine IL-6 secretion. This sti ll allows an IL-6 effect in the presence of IL-10 which appears adapti ve with a view to the converging effects of these two cytokines on hum an B lymphocytes. Our study thus adds to the appreciation of the compl ex cytokine regulation of the immune system.