T cells infiltrating inflammatory sites are usually of the activated/memory type. The precise mechanism for the positioning of these cells within tissues is unclear. Adhesion molecules certainly play a role; however, the intricate control of cell migration appears to be mediated by numerous chemokines and their receptors. Particularly important chemokines for activated/memory T cells are the CXCR3 ligands IP-10 and Mig and the CCR5 ligands RANTES, macrophage inflammatory protein-1alpha, and macrophage inflammatory protein-1beta. We raised anti-CXCR3 mAbs and were able to detect high levels of CXCR3 expression on activated T cells. Surprisingly, a proportion of circulating blood T cells, B cells, and natural killer cells also expressed CXCR3. CCR5 showed a similar expression pattern as CXCR3, but was expressed on fewer circulating T cells. Blood T cells expressing CXCR3 (and CCR5) were mostly CD45RO+, and generally expressed high levels of beta1 integrins. This phenotype resembled that of T cells infiltrating inflammatory lesions. Immunostaining of T cells in rheumatoid arthritis synovial fluid confirmed that virtually all such T cells expressed CXCR3 and approximately 80% expressed CCR5, representing high enrichment over levels of CXCR3+ and CCR5+ T cells in blood, 35 and 15%, respectively. Analysis by immunohistochemistry of various inflamed tissues gave comparable findings in that virtually all T cells within the lesions expressed CXCR3, particularly in perivascular regions, whereas far fewer T cells within normal lymph nodes expressed CXCR3 or CCR5. These results demonstrate that the chemokine receptor CXCR3 and CCR5 are markers for T cells associated with certain inflammatory reactions, particularly TH-1 type reactions. Moreover, CXCR3 and CCR5 appear to identify subsets of T cells in blood with a predilection for homing to these sites.

Lymphocytes that are responsible for regional (tissue-specific) immunity home from the blood to the intestines, inflamed skin or other sites through a multistep process involving recognition of vascular endothelial cells and extravasation. Chemoattractant cytokine molecules known as chemokines regulate this lymphocyte traffic, in part by triggering arrest (stopping) of lymphocytes rolling on endothelium. Here we show that many systemic memory T cells in blood carry the chemokine receptor CCR4 and therefore respond to its ligands, the chemokines TARC and MDC. These cells include essentially all skin-homing cells expressing the cutaneous lymphocyte antigen and a subset of other systemic memory lymphocytes; however, intestinal (alpha4beta7+) memory and naive T cells respond poorly. Immunohistochemistry reveals anti-TARC reactivity of venules and infiltration of many CCR4+ lymphocytes in chronically inflamed skin, but not in the gastrointestinal lamina propria. Moreover, TARC induces integrin-dependent adhesion of skin (but not intestinal) memory T cells to the cell-adhesion molecule ICAM-1, and causes their rapid arrest under physiological flow. Our results suggest that CCR4 and TARC are important in the recognition of skin vasculature by circulating T cells and in directing lymphocytes that are involved in systemic as opposed to intestinal immunity to their target tissues.

Multiple sclerosis (MS) is a T cell-dependentChemokines, chemotactic cytokines that mediate the attraction of leukocytes to tissues, are essential for inflammatory responses. More than 40 chemokines and 10 chemokine receptors are known, as recently reviewed (1). Recent data suggest a bias in expression of selected chemokine receptors by Th1 cells compared with Th2 cells. In particular, human Th1 clones express CXCR3 (receptor for IP-10 and Mig) and CCR5 (receptor for MIP-1␣, MIP-1␤, and RANTES), whereas Th2 cells express CCR3 (receptor for eotaxin, RANTES, MCP-3, MCP-4), CCR4 (receptor for TARC and MDC) (2-4) and CCR8 (receptor for I-309) (5).Multiple sclerosis (MS) is a T cell-dependent chronic inflammatory disease of the central nervous system with a likely autoimmune etiology (6). A central mechanism in the pathogenesis of MS is the organ-specific traffic of T cells into the brain. Though it is known that activated T cells can cross the blood-brain barrier, the mechanisms by which activated T cells are recruited and remain in the brain, and whether chemokines are involved in the pathogenesis of MS, are unknown. Chemokine receptors that are expressed by Th1 cells may be especially important, as increased production of interferon-␥ (IFN-␥) precedes clinical attacks (7, 8) and injection of MS patients with recombinant IFN-␥ induced exacerbations of the disease (9). In addition, MS involves different stages, usually beginning with a relapsing-remitting phase and later, a progressive form. Immune factors associated with different stages of the disease are not well understood. We studied chemokine receptor expression by mononuclear cells in MS. We found that the numbers of CXCR3 ϩ T cells were increased in relapsing-remitting MS and that both CCR5

Chemokine receptors serve as coreceptors for HIV entry into CD4+ cells. Their expression is thought to determine the tropism of viral strains for different cell types, and also to influence susceptibility to infection and rates of disease progression. Of the chemokine receptors, CCR5 is the most important for viral transmission, since CCR5 is the principal receptor for primary, macrophage-tropic viruses, and individuals homozygous for a defective CCR5 allele (Δ32/ Δ32) are highly resistant to infection with HIV-1. In this study, CCR5-specific mAbs were generated using transfectants expressing high levels of CCR5. The specificity of these mAbs was confirmed using a broad panel of chemokine receptor transfectants, and by their non-reactivity with T cells from Δ32/Δ32 individuals. CCR5 showed a distinct pattern of expression, being abundant on long-term activated, IL-2–stimulated T cells, on a subset of effector/memory T cells in blood, and on tissue macrophages. A comparison of normal and CCR5 Δ32 heterozygotes revealed markedly reduced expression of CCR5 on T cells from the heterozygotes. There was considerable individual to individual variability in the expression of CCR5 on blood T cells, that related to factors other than CCR5 genotype. Low expression of CCR5 correlated with the reduced infectability of T cells with macrophage-tropic HIV-1, in vitro. Anti-CCR5 mAbs inhibited the infection of PBMC by macrophage-tropic HIV-1 in vitro, but did not inhibit infection by T cell–tropic virus. Anti-CCR5 mAbs were poor inhibitors of chemokine binding, indicating that HIV-1 and ligands bind to separate, but overlapping regions of CCR5. These results illustrate many of the important biological features of CCR5, and demonstrate the feasibility of blocking macrophage-tropic HIV-1 entry into cells with an anti-CCR5 reagent.