Purity >95% as determined by SDS-PAGE. Interleukin 15 (IL-15) is a widely expressed proinflammatory cytokine that is structurally and functionally related to interleukin 2 (IL-2). IL-15 signals through JAK kinases to activate STAT3, STAT5, and STAT6 transcription factors. IL-15 regulates the activation of T cells, neutrophils, and macrophages, and is a stimulatory cytokine promoting dendritic cell function. IL-15 expression is dysregulated in chronic inflammatory disorders, including rheumatoid arthritis, psoriasis, and pulmonary inflammatory diseases. Therefore, IL-15 may serve as an effective therapeutic target, due to the beneficial outcomes of IL-15 neutralization in models of psoriasis and diabetes.