Cytokine

Cytokines are a broad and loose category of small <a href="/facts/Protein/Jxmagu3E">proteins</a> (~5–25 <a href="/facts/KDa/dSQWav5t">kDa</a>) important in <a href="/facts/Cell_signaling/6oYAVP9I">cell signaling</a>. 
Due to their size, cytokines cannot cross the <a href="/facts/Lipid_bilayer/CQKQ9l3g">lipid bilayer</a> of cells to enter the <a href="/facts/Cytoplasm/Wa0sE6xf">cytoplasm</a> and therefore typically exert their functions by interacting with specific <a href="/facts/Cytokine_receptor/4wVuJDmm">cytokine receptors</a> on the target cell surface. 
Cytokines have been shown to be involved in <a href="/facts/Autocrine_signaling/EwfQEYzG">autocrine</a>, <a href="/facts/Paracrine_signaling/V8eVwG9z">paracrine</a> and <a href="/facts/Endocrine_signaling/PDvN5cpj">endocrine signaling</a> as <a href="/facts/Immunomodulation/fWlbBnHc">immunomodulating agents</a>. 
Cytokines include <a href="/facts/Chemokine/YrySj9eD">chemokines</a>, <a href="/facts/Interferon/63XfwpEh">interferons</a>, <a href="/facts/Interleukin/a8qBzb0E">interleukins</a>, <a href="/facts/Lymphokine/FWIfyQBv">lymphokines</a>, and <a href="/facts/Tumour_necrosis_factor/5G0MA0dG">tumour necrosis factors</a>, but generally not <a href="/facts/Hormone/WFnBnINJ">hormones</a> or <a href="/facts/Growth_factor/D1xnRbcH">growth factors</a> (despite some <a href="/facts/Growth_factor/D1xnRbcH">overlap in the terminology</a>). 
Cytokines are produced by a broad range of cells, including immune cells like <a href="/facts/Macrophage/z7hkQu3o">macrophages</a>, <a href="/facts/B_cell/6Y1tgwwp">B lymphocytes</a>, <a href="/facts/T_cell/5z6PQ9UN">T lymphocytes</a> and <a href="/facts/Mast_cell/szfXss5q">mast cells</a>, as well as <a href="/facts/Endothelium/L4ENFVnw">endothelial cells</a>, <a href="/facts/Fibroblast/n08KsFll">fibroblasts</a>, and various <a href="/facts/Stromal_cell/31AA691H">stromal cells</a>; a given cytokine may be produced by more than one type of cell. 
Cytokines act through <a href="/facts/Cell_surface_receptor/0YGSjDdL">cell surface receptors</a> and are especially important in the <a href="/facts/Immune_system/HRCTf1pb">immune system</a>; cytokines modulate the balance between <a href="/facts/Humoral_immunity/qG9I4pGf">humoral</a> and <a href="/facts/Cell-mediated_immunity/vPX39rt1">cell-based</a> immune responses, and they regulate the maturation, growth, and responsiveness of particular cell populations. Some cytokines enhance or inhibit the action of other cytokines in complex ways.Cytokines are also released in lower concentrations than hormones. 
Cytokines are important in health and disease, specifically in host <a href="/facts/Immune_response/dtLulqIy">immune responses</a> to <a href="/facts/Infection/182XrncP">infection</a>, <a href="/facts/Inflammation/Ura86MIy">inflammation</a>, <a href="/facts/Major_trauma/vAIyyy22">trauma</a>, <a href="/facts/Sepsis/n52bkffJ">sepsis</a>, <a href="/facts/Cancer/PVW6n1D0">cancer</a>, and reproduction.

Cytokine open-in-new

Cytokine