citokine

Cytokines are a broad category of small secreted proteins that mediate and regulate immunity, inflammation, and hematopoiesis. They are produced by a range of cells, including macrophages, dendritic cells, T and B lymphocytes, endothelial cells, and fibroblasts, in response to infection or injury. Cytokines exert their effects by binding to specific receptors on target cells, triggering intracellular signaling cascades such as JAK-STAT, MAPK, and NF-κB pathways. This leads to altered gene expression and diverse outcomes, from cell growth and differentiation to recruitment of immune cells.

Functions and classification: They can act locally (paracrine) or at a distance (endocrine). They are often grouped by function into interleukins, interferons, tumor necrosis factors, chemokines, and growth factors. Many cytokines are pleiotropic, redundant, synergistic, or antagonistic, contributing to the complex regulation of immune responses.

Roles in health and disease: Cytokines coordinate responses to infection, inflammation, and tissue repair. Dysregulated cytokine production is linked to autoimmune diseases (for instance TNF-α in rheumatoid arthritis), allergic conditions, and cancer. A hyperinflammatory overproduction, known as a cytokine storm, can cause severe tissue damage and organ failure in infections and some therapies.

Clinical use and research: Cytokines or cytokine-modulating therapies are used clinically, such as interferons in viral infections and certain cancers; monoclonal antibodies or receptor antagonists targeting specific cytokines (for example TNF inhibitors or IL-6 receptor blockers) are used in autoimmune diseases. Ongoing research explores cytokine networks to better modulate immune responses with fewer side effects.