Chemokines play well established roles as attractants of naive and effector
T cells. New studies indicate that chemokines also have roles in regulatin
g T cell differentiation. Blocking G(i) protein-coupled receptor signaling
by pertussis toxin as well as deficiencies in G alpha (i2), chemokine recep
tor 2 (CCR2), CCR5, chemokine ligand 2 (CCL2, also known as monocyte chemoa
ttractant protein 1, or MCP-1), CCL3 (macrophage inflammatory protein 1 alp
ha, or MIP-1 alpha) and CCL5 (RANTES) have all been found to have effects o
n the magnitude and cytokine polarity of the T cell response. Here we focus
on findings in the CCL2-CCR2 and CCL3-CCR5 ligand-receptor systems. The ro
les of these molecules in regulating T cell fate include possible indirect
effects on antigen-presenting cells and direct effects on differentiating T
cells. Models to account for the action of chemokines and G protein-couple
d receptor signals in regulating T cell differentiation are discussed.