We examined the ability of chemokine receptors and related G protein-coupled receptors to facilitate infection by primary, clinical HIV-1 isolates. CCR5, when expressed along with CD4, the HIV-1 receptor, allowed cell lines resistant to most primary HIV-1 isolates to be infected. CCR3 facilitated infection by a more restricted subset of primary viruses, and binding of the CCR3 ligand, eotaxin, inhibited infection by these isolates. Utilization of CCR3 and CCR5 on the target cell depended upon the sequence of the third variable (V3) region of the HIV-1 gp120 exterior envelope glycoprotein. The ability of various members of the chemokine receptor family to support the early stages of HIV-1 infection helps to explain viral tropism and beta-chemokine inhibition of primary HIV-1 isolates.

TECK (thymus-expressed chemokine), a recently described CC chemokine expressed in thymus and small intestine, was found to mediate chemotaxis of human G protein–coupled receptor GPR-9-6/L1.2 transfectants. This activity was blocked by anti–GPR-9-6 monoclonal antibody (mAb) 3C3. GPR-9-6 is expressed on a subset of memory α4β7high intestinal trafficking CD4 and CD8 lymphocytes. In addition, all intestinal lamina propria and intraepithelial lymphocytes express GPR-9-6. In contrast, GPR-9-6 is not displayed on cutaneous lymphocyte antigen–positive (CLA+) memory CD4 and CD8 lymphocytes, which traffic to skin inflammatory sites, or on other systemic α4β7−CLA− memory CD4/CD8 lymphocytes. The majority of thymocytes also express GPR-9-6, but natural killer cells, monocytes, eosinophils, basophils, and neutrophils are GPR-9-6 negative. Transcripts of GPR-9-6 and TECK are present in both small intestine and thymus. Importantly, the expression profile of GPR-9-6 correlates with migration to TECK of blood T lymphocytes and thymocytes. As migration of these cells is blocked by anti–GPR-9-6 mAb 3C3, we conclude that GPR-9-6 is the principal chemokine receptor for TECK. In agreement with the nomenclature rules for chemokine receptors, we propose the designation CCR-9 for GPR-9-6. The selective expression of TECK and GPR-9-6 in thymus and small intestine implies a dual role for GPR-9-6/CCR-9, both in T cell development and the mucosal immune response.

Interleukin-8 (IL-8) is one of the major mediators of the inflammatory response. The pathways by which IL-8 activates inositide-specific phospholipase C (PLC) were investigated by co-expression of different components of the guanosine triphosphate binding protein (G protein) pathway in COS-7 cells. Two distinct IL-8 receptors reconstituted ligand-dependent activation of endogenous PLC when transfected together with the G protein alpha subunits G alpha 14, G alpha 15, or G alpha 16. However, reconstitution was not observed with cells that overexpressed G alpha q or G alpha 11. Furthermore, IL-8 receptors interacted with endogenous pertussis toxin-sensitive G proteins or with the recombinant G protein Gi to release free beta gamma subunits that could then specifically activate the beta 2 isoform of PLC. These findings suggest that IL-8 acts through signal-transducing pathways that are limited to specific heterotrimeric G proteins and effectors. These may provide suitable targets for the development of anti-inflammatory agents.

Eosinophil leukocytes express high numbers of the chemokine receptor CCR3 which binds eotaxin, monocyte chemotactic protein (MCP)-4, and some other CC chemokines. In this paper we show that CCR3 is also highly expressed on human blood basophils, as indicated by Northern blotting and flow cytometry, and mediates mainly chemotaxis. Eotaxin and MCP-4 elicited basophil migration in vitro with similar efficacy as regulated upon activation normal T cells expressed and secreted (RANTES) and MCP-3. They also induced the release of histamine and leukotrienes in IL-3-primed basophils, but their efficacy was lower than that of MCP-1 and MCP-3, which were the most potent stimuli of exocytosis. Pretreatment of the basophils with a CCR3-blocking antibody abrogated the migration induced by eotaxin, RANTES, and by low to optimal concentrations of MCP-4, but decreased only minimally the response to MCP-3. The CCR3-blocking antibody also affected exocytosis: it abrogated histamine and leukotriene release induced by eotaxin, and partially inhibited the response to RANTES and MCP-4. In contrast, the antibody did not affect the responses induced by MCP-1, MCP-3, and macrophage inflammatory protein-1 ␣ , which may depend on CCR1 and CCR2, two additional receptors detected by Northern blotting with basophil RNA. This study demonstrates that CCR3 is the major receptor for eotaxin, RANTES, and MCP-4 in human basophils, and suggests that basophils and eosinophils, which are the characteristic effector cells of allergic inflammation, depend largely on CCR3 for migration towards different chemokines into inflamed tissues. ( J. Clin. Invest. 1997. 100:1137-1143.)

These findings are of interest for the development of alpha7-nicotinic acetylcholine receptor agonists as a new class of anti-inflammatory therapeutics.