A novel secreted cytokine, termed IL-17F, was cloned using nested RACE PCR. This cytokine bears homology to IL-17. IL-17F was expressed only in activated CD4+ T cells and activated monocytes. Recombinant human IL-17F did not stimulate the proliferation of hematopoietic progenitors or the migration of mature leukocytes. However, it markedly inhibited the angiogenesis of human endothelial cells and induced endothelial cells to produce IL-2, TGF-β, and monocyte chemoattractant protein-1.

A novel cytokine termed IL-17D was cloned using nested RACE PCR. It is a secreted cytokine with homology to the IL-17 family of proteins. IL-17D is preferentially expressed in skeletal muscle, brain, adipose tissue, heart, lung, and pancreas. Treatment of endothelial cells with purified rIL-17D protein stimulated the production of IL-6, IL-8, and GM-CSF. The increased expression of IL-8 was found to be NF-κB-dependent. rIL-17D also demonstrated an inhibitory effect on hemopoiesis of myeloid progenitor cells in colony formation assays.

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