Interleukin 1 represents two proteins. IL-1a and IL-1b are two genetically distinct but related proteins which recognize the same surface receptors. IL-1 is not typically produced by healthy individuals, though various laboratory mice strains will display constitutive levels serum expression of IL-1, though this may be attributed to mode of sample collection. In response to proinflammatory stimulation, however, high levels of IL-1 are expressed. stimulation, IL-1 is a proinflammatory cytokine expressed by multiple cell types.

Both the alpha and beta forms of IL-1 are synthesized in preform which is partially membrane associated and partially stored for quick cleavage and release upon stimulation. IL-1a and IL-1b differ at the amino acid level, showing only 25% similarity, and also in activity in the pre and processed forms. Unprocessed IL-1a remains biologically acitive, while IL-1b has little or no biological activity while unprocessed. Both forms have nearly the same effect produced by binding to specific receptors. Two distinct receptors from the Ig superfamily have been isolated. IL-1 RI isolated mainly from endothelial cells, fibroblasts, hepatocytes, keratinocytes, and T cells; while IL-1 RII is found on B-cells, bone marrow cells and neutrophils predominantly. IL-1a preferentially binds to IL-1 RI while IL-1b binds better to IL-1 RII though each will stimulated both receptors.

IL-1 has been shown to have diverse biological functions though best konwn for its immunological roles inducing inflammation. The presence of IL-1 will stimulated cell adhesion molecule upregulation, MMP expression and activation of numerous cells, including: macrophages/monocytes, T-cells, B-cells, NK cells, and LAK cells. It induces proinflammatory cytokines in macrophages/monocytes such as TNFa and IL-6, while inducing TC to secreted IL-2, IL-4 and GM-CSF. In combination with IL-6 it induces B-cell proliferation. IL-1 is also known to induce prostaglandin synthesis in endothelial cells, activate protein and albumin synthesis in the liver, induce insulin production in pancreas, induce fever in the brain, collagenase production in synovial cells, and cartliage resorption in bones. Excessive or prolonged production of IL-1 has been observed in pancreatic beta cell destruction, sepsis, autoimmunity, leukemia, diabetes mellitus, and atherosclerosis.

In summary, IL-1a and IL-1b are early phase cytokines present in many disease pathologies. It's proinflammatory effects make it a significant regulator and inducer of diesease. In mixed cultures, it is commonly seen with: S IL-6, IL-12, IL-10, IFNy, TNFa and numerous chemokines.