Introduction
Interleukin-10 (IL-10 or IL10), also known as human cytokine synthesis inhibitory factor (CSIF), is an anti-inflammatory cytokine. In humans, IL-10 is encoded by the IL10 gene. The IL-10 protein is a homodimer; each of its subunits is 178-amino-acid long. IL-10 is classified as a class-2 cytokine, a set of cytokines including IL-19, IL-20, IL-22, IL-24 (Mda-7), and IL-26, interferons (IFN-alpha, -beta, -epsilon, -kappa, -omega, -delta, -tau, and -gamma) and interferon-like molecules (limitin, IL-28A, IL-28B, and IL-29). In humans, IL-10 is encoded by the IL10 gene, which is located on chromosome 1 and comprises 5 exons, and is primarily produced by monocytes and, to a lesser extent, lymphocytes, namely type 2 T helper cells (TH2), mastocytes, CD4+CD25+Foxp3+ regulatory T cells, and in a certain subset of activated T cells and B cells. IL-10 can be produced by monocytes upon PD-1 triggering in these cells.