Human IL-1ra/IL-1F3 DuoSet ELISA

Human IL-1ra is synthesized as a 177 aa precursor that contains a 25 aa signal sequence and a 152 aa mature region (10, 11). Although it contains an IL-1 cytokine fold, it apparently lacks two structural motifs that allow for activation of the IL-1 receptor heterodimer. First, and following binding to IL-1 RI, the presence of Ile 51-His 54 and Lys 145 of the mature molecule preclude recruitment of IL-1 R AcP. Second, there is no identifiable C-terminal lectin segment that is hypothesized to help recruit an accessory signaling component (1, 12, 13). Mature human IL-1ra is 77% and 82% aa identical to mouse and canine IL-1ra, respectively, and human IL-1ra inhibits IL-1 activity on mouse cells (10). A number of cell types express IL-1ra, including monocytes (11), Sertoli cells (14), hepatocytes (15), adipocytes (16), synovial fibroblasts (17), mast cells (18), pancreatic beta-cells (19), and intestinal epithelial cells (20). There are at least three intracellular IL-1ra isoforms (icIL-1ra1, 2, and 3). All show N-terminal variation, and all contain amino acids 35-177 of the secreted precursor (21-23). Intracellular IL-1ra1 is of particular interest, because it is reported to be "secreted" by endothelial cells and binds to the IL-1 RI in an antagonist fashion (23-25). Intracellular IL-1ra1 is 159 aa in length and shows a 3 aa substitution for the first 21 aa's of the signal sequence of IL-1ra (21).