IL-10 inhibits apoptotic cell death in human T cells starved of IL-2

Abstract

IL-10 was originally described as an inhibitory factor produced by murine T_h2 lymphocytes that suppresses IFN-_γ production by activated murine T_h1 lymphocytes. In this study, we have analyzed the effect of human IL-10 on human T cell death induced by IL-2 deprivation. IL-2-dependent T lymphocytes rapidly die when deprived of IL-2. This cell death was found to involve loss of cell volume, chromatin condensation, and DNA fragmentation, all characteristic of apoptosis. After 2 days incubation in culture medium without IL-2, the viability of TM11 cells (a tetanus toxoid-specific T cell line) and of activated peripheral blood T cells decreased from >98% to 34.3 (±2.9) and 39.7 (±5.5)% respectively. Addition of purified human IL-10 (100 U/ml) to these IL-2-starved cells significantly improved cell viability (66.0±6.0 and 73.1±12.3% respectively, P=0.0051). This protective effect of IL-10 was dose-dependent and was neutralized by the anti-human IL-10 mAb 19F1. It was neither accompanied by T cell growth stimulation as judged by [³H] thymidine incorporation nor neutralized by anti-IL-2 or anti-IL-2 receptor (CD25) antibodies. Analysis of DNA after separation on agarose gels revealed that IL-10 inhibits DNA fragmentation in IL-2-starved T cells. T cells protected from death by IL-10 were indistinguishable from IL-10-untreated viable T cells in the ability to proliferate in response to IL-2. Thus, another property of IL-10 is to promote the survival of IL-2-dependent T cells otherwise destined to die by apoptosis.