Cytokines are a broad and diverse group of small proteins that play crucial roles in cell signaling and communication within the immune system and other physiological processes. They are produced by various cell types, including immune cells such as macrophages, T cells, and B cells, as well as endothelial cells, fibroblasts, and others.
There are numerous types of cytokines, including interleukins, interferons, tumor necrosis factors (TNFs), chemokines, growth factors, and others. Each type of cytokine has specific functions and can interact with various receptors on target cells, triggering specific cellular responses.
Cytokines serve as molecular messengers that regulate immune responses, inflammation, hematopoiesis (the formation of blood cells), cell proliferation, differentiation, and cell death. They can act locally, affecting nearby cells (paracrine signaling), or they can act systemically, influencing distant cells (endocrine signaling).