Cytokines: Key Messengers of the Immune System
Cytokines are small proteins that play a crucial role in communication between cells, particularly within the immune system. Acting as chemical messengers, they help regulate immune responses, inflammation, cell growth, and tissue repair. Although they are produced in tiny amounts, cytokines have powerful effects on how the body responds to infection, injury, and disease.
Cytokines are secreted by a wide range of cells, including immune cells such as macrophages, T lymphocytes, B lymphocytes, and natural killer cells, as well as non-immune cells like endothelial and epithelial cells. Once released, cytokines bind to specific receptors on target cells, triggering signaling pathways that alter gene expression and cellular behavior. Their actions can be local (autocrine or paracrine) or systemic (endocrine), depending on the context and concentration.
There are several major categories of cytokines, each with distinct functions. Interleukins (ILs) primarily mediate communication between white blood cells and are essential for coordinating immune responses. Interferons (IFNs) play a key role in antiviral defense by inhibiting viral replication and activating immune cells. Tumor necrosis factors (TNFs) are involved in inflammation and apoptosis, while chemokines guide the movement of immune cells to sites of infection or injury. Colony-stimulating factors (CSFs) regulate the production and differentiation of blood cells in the bone marrow.