The ␣-chemokine receptor fusin (CXCR-4) and ␤-chemokine receptor CCR5 serve as entry cofactors for T-cell (T)-tropic and macrophage (M)-tropic human immunodeficiency virus type 1 (HIV-1) strains, respectively, when expressed with CD4 in otherwise nonpermissive cells. Some M-tropic and dual-tropic strains can also utilize other ␤-chemokine receptors, such as CCR2b and CCR3. A mutation of CCR5 (⌬ccr5) was recently found to be common in certain populations and appears to confer protection against HIV-1 in vivo. Here, we show that this mutation results in a protein that is expressed intracellularly but not on the cell surface. Primary CD4 T cells from ⌬ccr5 homozygous individuals were highly resistant to infection with prototype M-tropic HIV-1 strains, including an isolate (YU-2) that uses CCR5 and CCR3, but were permissive for both a T-tropic strain (3B) and a dual-tropic variant (89.6) that uses CXCR-4, CCR5, CCR3, or CCR2b. These cells were also resistant to M-tropic patient isolates but were readily infected by T-tropic patient isolates. Primary macrophages from ⌬ccr5 homozygous individuals were also resistant to infection with M-tropic strains, including YU-2, but the dual-tropic strain 89.6 was able to replicate in them even though macrophages are highly resistant to CXCR-4-dependent T-tropic isolates. These data show that CCR5 is the essential cofactor for infection of both primary macrophages and T lymphocytes by most M-tropic strains of HIV-1. They also suggest that CCR3 does not function for HIV-1 entry in primary lymphocytes or macrophages, but that a molecule(s) other than CCR5 can support entry into macrophages by certain virus isolates. These studies further define the cellular basis for the resistance to HIV-1 infection of individuals lacking functional CCR5.

Human immunodeficiency virus type 1 (HIV-1) infection is highly compartmentalized, with distinct viral genotypes being found in the lungs, brain, and other organs compared with blood. CCR5 and CXCR4 are the principal HIV-1 coreceptors, and a number of other molecules support entry in vitro but their roles in vivo are uncertain. To address the relationship between tissue compartmentalization and the selective use of entry coreceptors, we generated functionalenv clones from primary isolates derived from the lungs and blood of three infected individuals and analyzed their use of the principal, secondary, orphan, and virus-encoded coreceptors for fusion. All Env proteins from lung viruses used CCR5 but not CXCR4, while those from blood viruses used CCR5 or CXCR4 or both. The orphan receptor APJ was widely used for fusion by Env proteins from both blood and lung viruses, but none used the cytomegalovirus-encoded receptor US28. Fusion mediated by the secondary coreceptors CCR2b, CCR3, CCR8, and CX3CR1 and orphan receptors GPR1, GPR15, and STRL33 was variable and heterogeneous, with relatively broad utilization byenv clones from isolates of one subject but limited use byenv clones from the other two subjects. However, there was no clear distinction between blood and lung viruses in secondary or orphan coreceptor fusion patterns. In contrast to fusion, none of the secondary or orphan receptors enabled efficient productive infection. These results confirm, at the level of cofactor utilization, previous observations that HIV-1 populations in the lungs and blood are biologically distinct and demonstrate diversity within lung-derived as well as blood-derived quasispecies. However, the heterogeneity in coreceptor utilization among clones from each isolate and the lack of clear distinction between lung- and blood-derived Env proteins argue against selective coreceptor utilization as a major determinant of compartmentalization.

The neurokinin receptors responsible for transducing the airway obstruction resulting from capsaicin infusion were defined in the tracheally perfused guinea pig lung. In this lung preparation, buffer is perfused via the trachea and allowed to exit the lung through numerous small holes in the pleural surface; airway obstruction is monitored as the backpressure (Pao) generated at a constant perfusion flow rate. Infusion of the specific NK1 receptor agonist, Sar-9 Met02(11) substance P, resulted in an increase in Pao; this effect was prevented by the NK1 receptor antagonist CP 99,994 but not by the NK2 receptor antagonist SR 48,968. Infusion of the specific NK2 receptor agonist Nle10-neurokinin A 4-10 resulted in an increase in Pao; this effect was prevented by the NK2 receptor antagonist SR 48,968 but not by the NK1 receptor antagonist CP 99,994. In the absence of NK receptor antagonists, infusion of capsaicin resulted in a significant increase in Pao, 31 +/- 4 cm H2O. In the presence of the NK1 receptor antagonist, the capsaicin response was not diminished, but in the presence of the NK2 receptor antagonist, the Pao response diminished to only 10 +/- 2 cm H2O, p < 0.001. These data indicate that when capsaicin is presented to the epithelial surface of the lung the resulting airway obstruction is mediated predominantly by NK2 receptor stimulation.

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