Cytokine Receptors and Signal Transduction

Cytokinesp lay a vital role in coordinating immune and inflammatory responses. Unlike growth factor receptors with a tyrosine kinase, cytokine receptors have no intrinsic tyrosine kinase activity. Based on their structure, cytokinere ceptors are classified into several groups. High affinity receptors for IL-2, IL-3, IL-5, IL-6, and GM-CSF are composed of at least two distinct subunits, α and β. The α subunits are primary cytokine binding proteins, and the β subunits are required for formation of high affinity binding sites as well as for signal transduction. The GM-CSF, IL-3, and IL-5 receptors appear to share the same β subunit in human, and therefore cross-talk among these cytokines may occur at the receptor level. High affinity receptors presumably are linked to various signal transduction pathways that lead to different cytokine functions. Differential expression of the cytokine receptors as well as reorganization of intracellular signalling pathways are critical for development of hemopoietic cells.