Tumor necrosis factor‐α and interleukin 6 synergistically induce T cell growth

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Abstract
T cells stimulated with phytohemagglutinin are dependent on monocyte‐derived helper signals (e.g. interleukin (IL) 6 and IL 1) for their proliferation. In the present study the effect of recombinant tumor necrosis factor α (rTNF‐α) as a helper signal for growth of highly purified peripheral blood human T cells stimulated with phytohemagglutinin was examined. TNF‐α alone had a weak co‐stimulatory effect, while a combination of TNF‐α and IL 6 provided highly effective synergistic helper signals for T cell proliferation. The effect of TNF‐α could not be ascribed to secondary induction of IL 1 production. The effect of TNF‐α on T cell proliferation was also found to be independent of the autocrine T cell growth factors IL 2 and IL 4. This latter points to dissimilarity between IL 1 and TNF‐α in the mechanism by which each of these two cytokines in combination with IL 6promotes T cell proliferation. TNF‐α, IL 6 and IL 1 thus seem to follow different pathways in their function as helper signals in T cell activation.