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.