Human Interleukin-17A (IL-17A) is encoded by the IL17A gene located on the chromosome 6 and belongs to the IL-17 family that contains IL-17A, IL-17B, IL-17C, IL-17D, IL-17E and IL-17F. They have a similar protein structure, with four highly conserved cysteine residues critical to their 3-dimensional shape, but no sequence similarity to any other known cytokines. Interleukin 17 is a T cell-expressed pleiotropic cytokine that exhibits a high degree of homology to a protein encoded by the ORF13 gene of herpesvirus Saimiri. Mature IL-17 containing one potential N-linked glycosylation site. Both recombinant and natural IL-17 have been shown to exist as disulfide linked homodimers. At the amino acid level, IL-17 exhibits 63 % amino acid identity with mouse IL-17. High levels of human IL-17 were induced from primary peripheral blood CD4+ T cells upon stimulation and they can induce stromal cells to produce proinflammatory and hematopoietic cytokines.