Ultraviolet-irradiated apoptotic lymphocytes produce interleukin-10 by themselves

Since inflammatory responses are rarely associated with apoptotic cell deat h, it is plausible that cells undergoing apoptosis may signal the immune sy stem to suppress inflammatory responses. By employing intracytoplasmic cyto kine staining in conjunction with annexin V-binding, we examined the repres entative pro-inflammatory cytokine tumor necrosis factor-alpha (TNF alpha) and anti-inflammatory cytokine interleukin-10 (IL-10) expression in ultravi olet (UV)-irradiated lymphocytes and analyzed them with apoptosis induction at a single cell level. We show here that lymphocytes exposed to UV result ed in IL-10 expression with marginal TNF alpha expression, and these IL-10- expressing cells underwent apoptosis. Addition of inhibitors for caspases b locked UV-induced apoptosis bur: not IL-10. These results indicate that UV elicited at least two types of signals: one which was caspase dependent, le ading to apoptosis, and another which was caspase independent, leading to I L-10 production. Lymphocyte apoptosis was thus found to link anti-inflammat ory cytokine secretion, and thereby may contribute to preventing unwanted i mmune responses. (C) 2000 Elsevier Science B.V. All rights reserved.