The chemokines family of small proteins are involved in numerous b- logical processes ranging from hematopoiesis, angiogenesis, and basal l- kocyte trafficking to the extravasation and tissue infiltration of leukocytes in response to inflammatory agents, tissue damage, and bacterial or viral infection. Chemokines exert their effects through a family of seven G-protein coupled transmembrane receptors. Worldwide interest in the chemokine field surged dramatically early in 1996, with the finding that certain chemokine receptors were the elusive coreceptors, required along with CD4, for HIV infection. Today, though over 40 human chemokines have been described, the n- ber of chemokine receptors lags behind—only 17 human chemokine receptors have been identified so far. What has emerged over the years is that most chemokine receptors bind several distinct ligands, and indeed the majority of chemokines are able to bind to multiple chemokine receptors, explaining to some extent the apparent disparity in the numbers of chemokines and rec- tors. Yet in spite of the apparent redundancy in chemokine/chemokine rec- tor interactions, it is clear that in vivo, spatial, temporal, and indeed cell- and tissue-specific expression of both chemokines and their receptors are imp- tant factors in determining the precise nature of cellular infiltrates in phy- ological and pathological processes.
