Chemokine Types

By Dr. Ananya Mandal, MDReviewed by Sally Robertson, B.Sc.

Chemokines belong to a family of proteins called the cytokines and are involved in initiating and guiding the recruitment and migration of immune cells to sites of infection or damage. Chemokines are small in size with a molecular weight of around 6 to 14 kilodaltons and contain around 70 to 125 amino acids.

Around 50 chemokines have been identified to date. Usually, chemokines have four cysteine residues that are key in providing their three dimensional shape. Members of the chemokine family can be divided into four main categories depending on how the first two cysteines are spaced.

CC chemokines

These have two adjacent cysteines near the N-terminus. These are called the CC chemokine ligands (CCLs). Twenty-seven members of this group have been identified and are numbered CCL-1 to CCL-28, as CLL-9 is the same as CCl-10. Most of the chemokines in this family contain four cysteines (C4-CC chemokines) but some contain six (C6-CC chemokines). CC chemokines trigger the movement of monocytes, natural killer cells and dendritic cells.

CXC chemokines

In the case of CXC chemokines, the two cysteines at the N-terminus are separated by an amino acid, which is denoted by an X. Seventeen CXC chemokines have been identified in mammals and are divided into two main groups. Those with the specific amino acid motif -glutamic acid-leucine-arginine - immediately before the first cycteine are termed ELR-positive and those without such a motif are described as ELR-negative.

The ELR-positive CXC chemokines interact with chemokine receptors CXCR1 and CXCR2 on the surface of neutrophils to induce their recruitment. The ELR-negative CXC chemokines mainly act by attracting lymphocytes towards them.

C chemokines

Members of the third group of chemokines are different to all other chemokines because they have only two cysteines, one at the N-terminus and one downstream. Only two of these chemokines have been identified and these are called XCL1 and XCL2.

CX3C chemokines

Members of this group have two cycteines at the N-terminus that are separated by three amino acids. Only one such chemokine has been discovered to date and is called fractalkine (or CX3CL1). It is both released by and bound to the cell that expresses it and acts as both a chemoattractant and a cell adhesion molecule.

Further Reading

• All Chemokine Content
• Chemokines - What are Chemokines?
• Chemokine Function
• Chemokine Structural Characteristics
• Chemokine Receptors