Cytokines are the chemical messengers of the immune system. Secreted by white blood cells and tissue cells, they affect immune cell interaction, communication and behaviour. Cytokines act locally, stimulating nearby cells into action.

Cytokines include interleukins, chemokines, interferons and factors such as tumor necrosis factor and granulocyte macrophage-colony stimulating factor. One example is interleukin-2 (IL-2), which is produced by activated CD4 Th1 T-cells. IL-2 stimulates the growth of other CD4 and CD8 T-cells and can help B-cells.

Chemokines have the ability to attract certain white blood cells, by causing them to move in a particular direction. This directional movement of a cell is known as chemotaxis. Chemokines include RANTES and the macrophage inflammatory proteins (MIP) 1 alpha and 1 beta.

In HIV infection, the normal levels and activities of some cytokines are disrupted. Consequently, some cytokines have been tested as experimental treatments for people with HIV. Certain chemokines may also play a part in facilitating or blocking HIVs entry into cells. Research is continuing into the role of cytokines in the immune system and, in particular, how cytokines affect HIV disease progression.

For more detail see Immune disruption in The immune system and HIV: How HIV damages the immune system.