Cytokines

Cytokines (formerly known as lymphokines, interleukins, and chemokines) are a group of signaling compounds that enable cells to communicate with each other. These compounds are water-soluble and made of proteins whose mass ranges between 8 to 30 kDa.

Cytokines are released by many cells within the body and are not limited to a single organ system. Because so many different types of cells use cytokines to communicate, their functions are as diverse as the cells that use them. They were originally identified within the immune system where they were found to mediate many immunological and inflammatory functions in response to trauma and disease.

All cytokines have receptors on cells. These receptors cause upregulation or downregulation of particular cellular functions (usually gene expression). Most cytokines are also pleiotropic (i.e., they cause different reactions in different cell types).

The endocrine functions of cytokines are particularly relevant in obesity. The excess adipose tissue, characteristic of obesity, releases large amounts of cytokines that affect almost every organ system within the body. Obesity-associated cytokine production has been thought to play a role in diabetes, hypertension, insulin resistance, arteriosclerosis, vascular endothelial dysfunction, triglyceride overproduction, very-low-density lipid overproduction, and a fall in high-density lipoproteins.

Cytokines that affect these diseases are believed to be derived from immune cells, such as macrophages, which accumulate in large numbers within the adipose tissue of obese individuals. These cells release large amounts of cytokines into the circulation and have numerous deleterious endocrine effects as outlined above.

Adipocytes themselves release cytokines such as leptin, which affect appetite, fat storage, insulin resistance, and reproductive functions. The exact interplay between the cytokines secreted by adipocytes, immune cells, and the rest of the body is incompletely understood and is a fertile ground for research as new cytokines with new functions are being discovered and characterized almost daily.