Cytokines are a class of small-molecule proteins synthesized and secreted by immune and non-immune cells. They facilitate intercellular communication and are extensively involved in various physiological processes such as immune responses, inflammatory reactions, and hematopoietic regulation. Acting on target cells via autocrine, paracrine, or endocrine pathways through specific surface receptors, they efficiently regulate cell proliferation, differentiation, activation, and function. Characterized by pleiotropy and redundancy, cytokines play a central role in anti-infection, anti-tumor immunity, and autoimmune diseases, making them significant therapeutic targets.