Potent induction of activin A secretion from monocytes and bone marrow stromal fibroblasts by cognate interaction with activated T cells

Activin A is a multifunctional cytokine essential for cell differentiation and apoptosis including erythroid cell differentiation in the bone marrow. In addition, activin A is induced by inflammation and exerts anti‐inflammatory effects. However, the mechanism of activin A induction is still unclear, especially by inflammatory processes. Here we show that activin A secretion from monocytes and bone marrow stromal fibroblasts, its major sources in the bone marrow, is markedly enhanced by cognate interaction with activated T cells. This process is mediated by CD40/CD40 ligand interaction as well as concomitantly secreted T cell‐derived cytokines, granulocyte macrophage‐colony stimulating factor, and interferon‐γ. Furthermore, stromal fibroblasts as well as monocytes provide a costimulatory signal to anti‐CD3‐treated T cells via CD80 and CD86 to maintain the enhanced activin A production. These findings suggest that activin A is potently induced in the bone marrow and may play a role in the suppression of inflammatory or immune processes.