Interleukin (IL)-4 indirectly suppresses IL-2 production by human T lymphocytes via peroxisome proliferator-activated receptor gamma activated by macrophage-derived 12/15-lipoxygenase ligands.

The respective development of either T helper type 1 (Th1) or Th2 cells is believed to be mediated by the effects of cytokines acting directly on Th precursors (Thp). We have generated evidence for an indirect monocyte-dependent immunoregulatory pathway. Recently, interleukin (IL) 4 has been shown to produce "new" potential peroxisome proliferator-activated receptor gamma (PPARgamma) ligands by inducing macrophage 12/15-lipoxygenase (12/15-LO). We have shown previously that the activated PPARgamma is a profound inhibitor of IL-2 transcription in human T lymphocytes. It is hypothetically possible that IL-4 might indirectly affect IL-2 production by Thp cells via macrophage-derived PPARgamma ligands. Using human monocytes and T lymphocytes from same donors, we have found that monocyte 12/15-LO products mediate the indirect inhibitory effect of IL-4 on anti-CD3- or phytohemagglutinin/phorbol 12-myristate 13-acetate-stimulated IL-2 production by T lymphocytes. We further analyzed which major 12/15-LO metabolites contributed to the above inhibition. 13-Hydroxyoctadecadienoic acid (13-HODE), a 12/15-LO product, markedly blocked IL-2 production by human blood T lymphocytes, but not Jurkat T cells. Moreover, the IL-4-conditioned macrophage medium contained a sufficient amount of 13-HODE and anti-13-HODE antibody indeed neutralized the inhibitory effects of the IL-4-conditional medium on T-cell IL-2 production. Using human T lymphocytes and the PPARgamma-transfected Jurkat T cells, we demonstrated the specific inhibition by 13-HODE of the transcription factors NFAT (nuclear factor of activated T cells) and nuclear factor kappaB, the IL-2 promoter reporter, and IL-2 production. However, 15-hydroxytetraenoic acid had little inhibitory effect. The potency of such inhibitory effects correlates well with the capability of the above metabolic lipids to activate PPARgamma. These data provide a mechanism whereby IL-4 may indirectly affect Thp function via PPARgamma activated by macrophage products of the 12/15-LO pathway.