Cytokines are small proteins that act as chemical messengers in the immune system, playing a crucial role in cell signaling to regulate immune responses and inflammation in the body. They are secreted by various cells, including immune cells like macrophages, T cells, B cells, and others, to communicate and coordinate the body's defense against infections, allergens, and tissue damage
. Cytokines function by binding to specific receptors on target cells, triggering responses such as immune cell activation, proliferation, differentiation, and directing cells where to go and what actions to take. They can act locally (paracrine), on the cell that secreted them (autocrine), or at distant sites via the bloodstream (endocrine)
. They are especially known for regulating inflammation, which is a key part of the immune response to fight pathogens and repair tissues. Cytokines can both promote and inhibit inflammation, maintaining a balance that is vital because excessive cytokine activity can lead to harmful conditions like autoimmune diseases or chronic inflammation
. Types of cytokines include interleukins, interferons, chemokines, lymphokines, and tumor necrosis factors, each with specific roles in immune modulation, cell growth, and hematopoiesis (blood cell formation)
. They are produced "on demand" rather than stored, and their signaling ultimately influences gene expression and protein production in target cells
. In summary, cytokines are essential proteins that regulate immune system communication, inflammation, and cellular behavior to protect the body and maintain health
