How cytokines signal messages within cells.

The intracellular signaling pathways used by cytokines to modulate the activity of immune effector cells have been the focus of intensive research. Cytokines interact with specific receptors on the plasma membrane, and this information is transduced into internal signals, often involving a cascade of kinases. These signals activate substrate proteins that serve as effectors within the cell. A number of protein kinase C substrates have been characterized. The function of one of these substrates, known as MARCKS (myristoylated alanine-rich C kinase substrate), appears to be important to the control of macrophage and neutrophil motility and may partially explain the modes of action of tumor necrosis factor and interleukin-8.