Human IL-36 alpha, previously called IL-1F6?and FIL1 epsilon ?(family of IL-1 member epsilon), is a?member of the IL-1 family which includes IL-1 beta, IL-1 alpha, IL-1ra, IL-18, and novel family members IL-36 Ra (IL-1F5), IL-36 beta (IL-1F8), IL-36 gamma (IL-1F9), IL-37 (IL-1F7) and IL?38 (IL?1F10) (1?4). All family members show a 12? beta ?strand, beta -trefoil configuration, and are believed to have arisen from a common ancestral gene (1,?2). IL-36 alpha is an 18?22?kDa, 158 amino acid (aa) intracellular and secreted protein that contains no signal sequence, no prosegment and no potential from N?linked glycosylation sites (1?3). It can be?released in response to LPS and the cell?ATP?induced activation of the P2X7 receptor (5). A 120?aa isoform missing aa 1?38 has been reported (6). Human IL?36 alpha (aa?6???158) shares 57?68% aa sequence identity with mouse, rabbit, equine and bovine IL?36 alpha and 27?57%?aa sequence identity with other novel IL?1 family members. IL?36 alpha is mainly found in skin and lymphoid tissues,?but?also?in fetal brain, trachea, stomach and intestine (1,?3,?7). It is expressed by monocytes, B?and T?cells (1,?2). The receptor for IL?36 alpha is a combination of IL?1?Rrp2 (also called IL1RL2 or IL?1?R6), mainly found in epithelia and keratinocytes, and the widely expressed IL?1?RAcP (3,?7). IL-36 alpha, beta, and gamma all activate NF-kappa B and MAPK pathways in an IL?1?Rrp2 dependent manner, and induce production of inflammatory cytokines and chemokines such as CXCL8/IL-8 (7). IL-36 alpha and?other?family members are overexpressed in psoriatic skin lesions, and transgenic overexpression of IL?36 alpha in skin keratinocytes produces epidermal hyperplasia (7?9). IL-36 alpha is present in kidney tubule epithelia, and?it is highly expressed in intubulointerstitial lesions in mouse models of chronic glomerulonephritis, lupus nephritis and diabetic nephritis (10).
