Interleukin 6 (IL-6) is a cytokine with pleiotropic effects on inflammation, immune response, and hematopoiesis. It is produced in response to infections and tissue injuries, stimulating acute phase responses, hematopoiesis, and immune reactions. While its expression is tightly regulated, dysregulated continuous synthesis of IL-6 contributes to chronic inflammation and autoimmunity. Tocilizumab, a humanized anti-IL-6 receptor antibody, has shown exceptional efficacy in treating rheumatoid arthritis and juvenile idiopathic arthritis, and is expected to be effective for other immune-mediated diseases. The mechanism of continuous IL-6 synthesis needs to be elucidated to develop more specific therapeutic approaches. IL-6 promotes the differentiation of naive CD4+ T cells, enhances antibody production, and regulates serum iron and zinc levels. It also stimulates bone resorption and osteoporosis, enhances angiogenesis, and aids keratinocyte proliferation. The regulation of IL-6 synthesis involves transcriptional and posttranscriptional mechanisms, including the actions of various transcription factors and microRNAs. The IL-6 receptor-signaling system, composed of IL-6R and gp130, triggers downstream signaling pathways such as JAK-STAT3 and JAK-SHP-2-mitogen-activated protein kinase. IL-6 is involved in various diseases, including rheumatoid arthritis, Castleman’s disease, systemic lupus erythematosus, and inflammatory myopathies. Tocilizumab has been approved for treating these conditions and is showing promise in off-label applications for other immune-mediated diseases. Further research is needed to understand the mechanisms underlying IL-6 persistence in certain diseases and to identify more specific therapeutic targets.Interleukin 6 (IL-6) is a cytokine with pleiotropic effects on inflammation, immune response, and hematopoiesis. It is produced in response to infections and tissue injuries, stimulating acute phase responses, hematopoiesis, and immune reactions. While its expression is tightly regulated, dysregulated continuous synthesis of IL-6 contributes to chronic inflammation and autoimmunity. Tocilizumab, a humanized anti-IL-6 receptor antibody, has shown exceptional efficacy in treating rheumatoid arthritis and juvenile idiopathic arthritis, and is expected to be effective for other immune-mediated diseases. The mechanism of continuous IL-6 synthesis needs to be elucidated to develop more specific therapeutic approaches. IL-6 promotes the differentiation of naive CD4+ T cells, enhances antibody production, and regulates serum iron and zinc levels. It also stimulates bone resorption and osteoporosis, enhances angiogenesis, and aids keratinocyte proliferation. The regulation of IL-6 synthesis involves transcriptional and posttranscriptional mechanisms, including the actions of various transcription factors and microRNAs. The IL-6 receptor-signaling system, composed of IL-6R and gp130, triggers downstream signaling pathways such as JAK-STAT3 and JAK-SHP-2-mitogen-activated protein kinase. IL-6 is involved in various diseases, including rheumatoid arthritis, Castleman’s disease, systemic lupus erythematosus, and inflammatory myopathies. Tocilizumab has been approved for treating these conditions and is showing promise in off-label applications for other immune-mediated diseases. Further research is needed to understand the mechanisms underlying IL-6 persistence in certain diseases and to identify more specific therapeutic targets.