IL-1 is a pyrogen, originally discovered in connection with fever responses to pathogens. IL-1 is an activating factor for lymphocytes also known to damage joints and influence liver protein levels. IL-1 is made by several cell types, including macrophages, monocytes, dendritic cells, B cells, NK cells, and epithelial cells. IL-1 upregulates endothelial cell adhesion molecule expression and can affect the hypothalamus and cause an increase in body temperature. IL-1α and -β are produced in pro-forms that require proteolytic cleavage to create the shorter, active form. IL-1 binds to the cell surface type I and II IL-1 receptors (IL-1RI and IL-1RII). IL-1α and -β and IL-1RA can compete for binding to these receptors. However, only IL-1RI, not IL-1RII, is functional because IL-1RII lacks a cytoplasmic domain and is thus unable to transmit signals to downstream steps.
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