Chemoattractants and their receptors in homeostasis and inflammation.

The study of leukocyte migration continues to provide new insights into the regulation of lymphocyte priming in secondary lymphoid organs and effector responses in inflamed tissues. Chemoattractant receptors have always been viewed as facilitators of cell movement into a tissue. This whole concept must now be revised with the discovery of sphingosine 1 phosphate receptors, which control cell exit from lymphoid tissues. The chemoattractants that regulate lymphoid tissue homing are usually different to those that regulate leukocyte recruitment to inflamed tissues. There is evidence, however, of inflammatory pathways of leukocyte recruitment in lymph nodes and, conversely of constitutive pathways in peripheral tissues. Finally, antagonists (or agonists) of chemoattractant receptors and their signalling pathways represent the most attractive strategy for the treatment of a wide range of inflammatory diseases, including allergy.