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Background
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IL-1α is a member of interleukin 1 family. IL-1α and IL-1β recognize the same IL-1 receptor and share a number of similar biological functions. IL-1α is predominantly a cell-associated molecule whereas IL-1β is a secreted molecule. IL-1α is synthesized primarily as a 31 kDa precursor that lacks a signal peptide. Cleavage of the precursor is via the cysteine protease calpain, resulting in a 17.5 kDa mature IL-1 molecule. Being active in the processed form, the IL-1 precursor is also biologically active via specific cell binding. A portion of the precursor is transported to the cell surface and associated with the cell membrane. Precursor IL-1α can be released and cleaved by extracellular proteases when the cells die, and can also be cleaved by activation of the calcium-dependent, membrane-associated calpains. Nearly all microbes and microbial products induce the production of IL-1α. Furthermore, IL-1α can be produced in monocytes and other cells in the 31 kDa precursor state. IL-1α can act on macrophages or monocytes by inducing its own synthesis as well as the production of TNF and IL-6. IL-1α induces the production of IL-2, IL-2 receptors, GM-CSF and IL-4 from activated T cells, stimulates B cell proliferation and maturation, and increases immunoglobulin synthesis. IL-1α affects NK cell activation and LAK production associated with other cytokines, and induces prostaglandin synthesis in endothelial cells and smooth muscle cells, collagenase production in synovial cells, and cartilage and calcium resorption in bones. Studies have shown a connection between IL-1α and the pathogenesis of endometriotic lesions. The increased expression of both matrix-degrading MMP-1 and its major stimulatory cytokine IL-1α in endometriotic lesions and the selective co-expression in the stroma of endometriotic foci clearly suggests the involvement of the IL-1α molecule in the pathogenic mechanisms leading to local invasion and tissue destruction. Reports also indicate that the translation of the neurotransmitter gene only occurs after receiving IL-1α stimulation. This effect was supressed by co-stimulation with IL-1 receptor antagonist. High levels of IL-1α are associated with sepsis, rheumatoid arthritis, inflammatory bowel disease, acute and chronic myelogenous leukemia, insulin-dependent diabetes mellitus, and atherosclerosis.
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