Chemokine receptor responses on T cells are achieved through regulation ofboth receptor expression and signaling

To address the issues of redundancy and specificity of chemokines and their receptors in lymphocyte biology, we investigated the expression of CC chem okine receptors CCR1, CCR2, CCR3, CCR5, CXCR3, and CXCR4 and responses to t heir ligands on memory and naive, CD4 and CD8 human T cells, both freshly i solated and after short term activation in vitro. Activation through CD3 fo r 3 days had the most dramatic effects on the expression of CXCR3, which wa s up-regulated and functional on all T cell populations including naive CD4 cells, In contrast, the effects of short term activation on expression of other chemokine receptors was modest, and expression of CCR2, CCR3, and CCR 5 on CD4 cells was restricted to memory subsets, In general, patterns of ch emotaxis in the resting cells and calcium responses in the activated cells corresponded to the patterns of receptor expression among T cell subsets. I n contrast, the pattern of calcium signaling among subsets of freshly isola ted cells did not show a simple correlation with receptor expression, so th e propensity to produce a global rise in the intracellular calcium concentr ation differed among the various receptors within a given T cell subset and for an individual receptor depending on the cell where it was expressed. O ur data suggest that individual chemokine receptors and their ligands funct ion on T tells at different stages of T cell activation/differentiation, wi th CXCR3 of particular importance on newly activated cells, and demonstrate T cell subset-specific and activation state-specific responses to chemokin es that are achieved by regulating receptor signaling as well as receptor e xpression.