Differential regulation of IgA production by TGF-β and IL-5: TGF-β induces surface IgA-positive cells bearing IL-5 receptor, whereas IL-5 promotes their survival and maturation into IgA-secreting cells☆

Abstract Transforming growth factor β (TGF-/3) and IL-5 have been shown to augment IgA production by LPS-stimulated murine B cells. We investigated the effect of TGF-β on the expression of surface Ig-isotype and IL-5 receptor on LPS-stimulated B cells. TGF-β increased the proportion of both surface IgA-positive (sIgA+) B cells and sIgG 2 b+ B cells and enhanced IgA and IgG 2 b production by LPS-stimulated B cells. TGF-β synergized with IL-5 only for IgA production of the seven Ig-isotypes and in combination with IL-5 caused a significant increase in the proportion of sIgA + B cells up to 17.4%. In contrast, IL-5 decreased the proportion of sIgG 2 b + B cells and sIgG 3 + B cells and inhibited the production of IgG 2 b and IgG 3 by LPS-stimulated B cells. About 50% of sIgA + cells induced by TGF-β expressed IL-5 receptor. They secreted peak levels of IgA and seemed to maintain long viability in the presence of IL-5; whereas TGF-β had the opposite effects on sIgA + B cells and down-regulated the IL-5 receptor expression. These results indicate that TGF-β increases the number of sIgA + - and IL-5 receptor-positive B cells which respond to IL-5 giving rise to IgA-secreting cells and also support the notions that TGF-β preferentially induces switching to sIgA + B cells and IL-5 induces the maturation of postswitch sIgA + B cells into IgA-secreting cells in a stepwise fashion.