Interleukin-6 (IL-6) is a multifunctional cytokine that plays a crucial role in regulating the immune response, inflammation, and various physiological processes. IL-6 is produced by a variety of cells, including T cells, B cells, monocytes, fibroblasts, endothelial cells, and adipocytes [1].
IL-6 is a pleiotropic cytokine that belongs to the interleukin family of proteins. IL-6 adopts a four-helix bundle structure, with helices A and D forming the receptor-binding site [2]. It is glycosylated, influencing stability and activity. IL-6 binds to IL-6 receptor (IL-6R), forming a hexameric complex with gp130, initiating downstream signaling via the JAK/STAT pathway. Conformational changes upon receptor binding facilitate signaling.
IL-6 has a primary involvement in the acute phase response, the immediate reaction to infection, injury, or inflammation. IL-6 stimulates the production of acute-phase proteins such as C-reactive protein (CRP), fibrinogen, and serum amyloid A, which help to enhance the immune response and facilitate tissue repair [3,4].
IL-6 plays a key role in the regulation of the immune system. It promotes the differentiation of B cells into antibody-producing plasma cells and stimulates the proliferation and activation of T cells, enhancing the adaptive immune response. IL-6 acts on various immune cells to modulate inflammation, promoting the recruitment of immune cells to sites of infection or injury [5,6]. IL-6 has diverse effects on different tissues and organs throughout the body. It has been implicated in the regulation of metabolism, with studies suggesting that IL-6 may play a role in energy balance, glucose metabolism, and lipid metabolism. IL-6 has been shown to have both pro- and anti-inflammatory effects depending on the context and the cells involved [7].
Dysregulated IL-6 signaling has been associated with various pathological conditions, including autoimmune diseases, chronic inflammation, and cancer. Elevated levels of IL-6 have been observed in conditions such as rheumatoid arthritis, systemic lupus erythematosus, and inflammatory bowel disease, where it contributes to tissue damage and disease progression [8].
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