Chemokines

Chemokines are a family of small cytokines, or signaling proteins secreted by cells, whose main function is to act as chemotactic agents—substances that induce the migration of cells toward the source of the chemokine. These molecules play critical roles in immune responses by directing the movement of circulating immune cells such as leukocytes from the blood into the tissues where their functions are required.

Classification

Chemokines are classified into four main subfamilies: CC chemokines, CXC chemokines, CX3C chemokines, and C chemokines, based on the arrangement of the first two of the conserved cysteine residues near their amino terminus. The classification is as follows:

• CC chemokines: The first two cysteines are adjacent to each other.
• CXC chemokines: There is one amino acid between the first two cysteines.
• CX3C chemokines: There are three amino acids between the two cysteines.
• C chemokines: Only one cysteine is present in the conserved location.

Function

Chemokines are primarily involved in the regulation of leukocyte trafficking in immune responses and inflammation. They are crucial in the body's defense against infections and play a role in diseases such as atherosclerosis, cancer, and HIV. Chemokines bind to specific G protein-coupled receptors on the surfaces of their target cells.

Immune Response and Inflammation

During an immune response, chemokines released by various cell types (including macrophages, endothelial cells, and fibroblasts) create a gradient that directs the migration of immune cells to sites of infection or injury. This process is essential for the initiation and maintenance of inflammation.

Role in Disease

Abnormal chemokine function is associated with a variety of diseases. For example, the overexpression of certain chemokines can lead to the recruitment of an excessive number of immune cells, which can cause tissue damage and contribute to the pathology of chronic inflammatory diseases. Conversely, some viruses, such as HIV, exploit chemokines and their receptors to infect target cells.

Research and Therapeutic Applications

Given their role in immune response and disease, chemokines and their receptors are attractive targets for drug development. Inhibitors of chemokine receptors are being studied for their potential to treat various diseases, including rheumatoid arthritis, multiple sclerosis, and HIV.

See Also

• Cytokine
• Immune system
• Inflammation

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