Figure 1.

The complex regulation of the chemokine (CK) system by a combination of agonist and antagonist activity illustrates why some CKs or chemokine receptors are not easy targets for immunomodulation and how different immunologic outcomes may occur. For example, CXCL9–11 are agonists at CXCR3 (expressing Th1 cells), but antagonists at CCR3 expressed by Th2 cells. Likewise, CCL5, CCL7, CCL8, CCL11, and CCL13 are agonists at CCR3-expressing Th2 cells. The typical stylized receptor depiction is meant to show the extracellular and intracellular domains of the receptor, which is a seven-transmembrane receptor.