INTERLEUKIN-10 INHIBITS ALLOGENEIC PROLIFERATIVE AND CYTOTOXIC T-CELL RESPONSES GENERATED IN PRIMARY MIXED LYMPHOCYTE-CULTURES

The effects of IL-10 on the generation of alloreactivity in primary mixed lymphocyte cultures (MLCs) were investigated. IL-10 inhibited in a dose-dependent fashion the alloantigen-induced proliferative responses. The suppressive effect was maximal when IL-10 was added at the beginning of the cultures, suggesting that it acts on the early stages of T cell activation. The proliferative responses were enhanced in the presence of a neutralizing anti-IL-10 mAb, indicating that endogenously produced IL-10 suppresses proliferation in primary MLC. The inhibitory effects of IL-10 were observed irrespective of whether irradiated allogeneic peripheral blood mononuclear cells, purified monocytes or freshly isolated B cells were used as stimulator cells. The proliferation of both the CD4+ and CD8+ T cell subsets was inhibited to a similar extent. The reduced proliferative responses were only minimally restored by high concentrations of exogenous IL-2, indicating that the effects of IL-10 are not exclusively due to inhibition of IL-2 synthesis. Furthermore, the production of IL-2, interferon (IFN)-gamma, IL-6, granulocyte macrophage colony stimulating factor, and tumor necrosis factor-alpha in primary MLCs was diminished by IL-10 and enhanced in the presence of anti-IL-10 mAb. The strongest effects were observed on the production of IFN-gamma. Although IL-10 reduces the proliferative responses, the ratios of CD3+CD4+ and CD3+CD8+ T cells remained the same in IL-10 treated and control cultures, yet the percentages of activated CD3+ T cells, as judged by CD25 and HLA-DR expression, were consistently reduced. The generation of allospecific cytotoxicity was also inhibited by IL-10 and enhanced in the presence of anti-IL-10 mAb. These data indicate that IL-10 has important regulatory effects on allogeneic responses in vitro.