The presence of IL-15 mRNA in many normal tissues and the increased production of IL-15 by macrophages/monocytes in response to bacterial or viral products suggests a role for IL-15 in protective immune responses, allograft rejection, and the pathogenesis of autoimmune diseases. Recently, a possible role for IL-15 in the pathogenesis of rheumatoid arthritis has been suggested. IL-15 is present in the synovial fluid of rheumatoid arthritis patients where it might contribute to recruitment of T cells and provide a means of stimulating T cells to produce macrophage-activating cytokines such as IFN-y. tumor necrosis factor a (TNFa) and granulocyte-macrophage colony-stimulating factor (GM-CSF).
Studies of IL-2 and IL-2Ra knockout mice have revealed that IL-2 provides an immunoregulatory role in the immune system that cannot be compensated for by IL-15 or other cytokines. Comparative studies using the IL-2, IL-2Ra, and IL-2R|3 knockout mice are likely to reveal defects in the IL-2R|3 knockout mice that can be attributed to the lack of both IL-2- and IL-15-mediated responses. The use of IL-15 antagonists in vivo and the generation of IL-15 knockout mice will provide further insight regarding the physiological roles of IL-15.
See also: Cytokines; Interleukin 2; Interleukin 2 receptor; Interleukin 12 and its receptor.
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