Interleukin 10, also known as cytokine synthesis inhibitory factor (CSIF), is the charter member of the IL-10 family of alpha -helical cytokines that also includesIL-19, IL-20, IL-22, IL-24, and IL-26/AK155 [1, 2]. IL-10 is secreted by many activated hematopoietic cell types as well as hepatic stellate cells, keratinocytes, and placental cytotrophoblasts [2-5]. Mature human IL-10 shares 72%-86% amino acid sequence identity with bovine, canine, equine, feline, mouse, ovine, porcine, and rat IL-10. Whereas human IL-10 is active on mouse cells, mouse IL-10 does not act on human cells [6, 7]. IL-10 is a 178 amino acid molecule that contains two intrachain disulfide bridges and is expressed as a 36 kDa noncovalently associated homodimer [6, 8, 9]. The IL-10 dimer binds to two IL-10 R alpha /IL-10 R1 chains, resulting in recruitment of two IL-10 R beta /IL-10 R2 chains and activation of a signaling cascade involving JAK1, TYK2, and STAT3 [10]. IL-10 R beta does not bind IL-10 by itself but is required for signal transduction [1]. IL-10 R beta also associates with IL-20 R alpha, IL-22R alpha, or IL-28 R alpha to form the receptor complexes for IL-22, IL-26, IL-28, and IL-29[11-13]. IL-10 is a critical molecule in the control of viral infections and allergic and autoimmune inflammation [14-16]. It promotes phagocytic uptake and Th2 responses but suppresses antigen presentation and Th1 proinflammatory responses [2].
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