No abstract

The opiates are well-established immunomodulatory factors, and recent evidence suggests that mu- and delta-opioid receptor ligands alter chemokine-driven chemotactic responses through the process of heterologous desensitization. In the present report, we sought to examine the capacity of mu- and delta-opioids to modulate the function of chemokine receptors CCR5 and CXCR4, the two major human immunodeficiency virus (HIV) coreceptors. We found that the chemotactic responses to the CCR1/5 ligand CCL5/regulated on activation, normal T expressed and secreted, but not the CXCR4 ligand stromal cell-derived factor-1alpha/CXCL12 were inhibited following opioid pretreatment. Studies were performed with primary monocytes and Chinese hamster ovary cells transfected with CCR5 and the micro-opioid receptor to determine whether cross-desensitization of CCR5 was a result of receptor internalization. Using radiolabeled-binding analysis, flow cytometry, and confocal microscopy, we found that the heterologous desensitization of CCR5 was not associated with a significant degree of receptor internalization. Despite this, we found that the cross-desensitization of CCR5 by opioids was associated with a decrease in susceptibility to R5 but not X4 strains of HIV-1. Our findings are consistent with the notion that impairment of the normal signaling activity of CCR5 inhibits HIV-1 coreceptor function. These results have significant implications for our understanding of the effect of opioids on the regulation of leukocyte trafficking in inflammatory disease states and the process of coreceptor-dependent HIV-1 infection. The interference with HIV-1 uptake by heterologous desensitization of CCR5 suggests that HIV-1 interaction with this receptor is not passive but involves a signal transduction process.

Strong evidence for the direct modulation of the immune system by opioids is well documented. Mu-opioids have been shown to alter the release of cytokines important for both host defense and the inflammatory response. Proinflammatory chemokines monocyte chemoattractant protein-1 (MCP-1), RANTES, and IFN-gamma-inducible protein-10 (IP-10) play crucial roles in cell-mediated immune responses, proinflammatory reactions, and viral infections. In this report, we show that [D-Ala(2),N:-Me-Phe(4),Gly-ol(5)]enkephalin (DAMGO), a mu-opioid-selective agonist, augments the expression in human PBMCs of MCP-1, RANTES, and IP-10 at both the mRNA and protein levels. Because of the proposed relationship between opioid abuse and HIV-1 infection, we also examined the impact of DAMGO on chemokine expression in HIV-infected cells. Our results show that DAMGO administration induces a significant increase in RANTES and IP-10 expression, while MCP-1 protein levels remain unaffected in PBMCs infected with the HIV-1 strain. In contrast, we show a dichotomous effect of DAMGO treatment on IP-10 protein levels expressed by T- and M-tropic HIV-infected PBMCs. The differential modulation of chemokine expression in T- and M-tropic HIV-1-infected PBMCs by opioids supports a detrimental role for opioids during HIV-1 infection. Modulation of chemokine expression may enhance trafficking of potential noninfected target cells to the site of active infection, thus directly contributing to HIV-1 replication and disease progression to AIDS.

The G protein-coupled 7 transmembrane (STM) chemoattractant receptors can be inactivated by heterologous desensitization. Earlier work showed that formly peptide receptor-like 1 (FPRL1), an STM receptor with low affinity for the bacterial chemotactic peptide formyl-methionylleucyl-phenylalamine (fMLF), is activated by peptide domains derived from the human immunodeficiency virus (HIV)-1 envelope glycoprotein gp120 and its activation results in desensitization and downregulation of the chemokine receptors CCR5 and CXCR4 from monocyte surfaces. This study investigated the possi- IntroductionChemokine receptors CCR5 and CXCR4 are 2 major coreceptors for human immunodeficiency virus (HIV)-1 infection and belong to the 7 transmembrane (STM), G protein-coupled receptor superfamily. 1 Such receptors are composed of 7 hydrophobic transmembrane domains, an N-terminus outside the cell surface, 3 extracellular and 3 intracellular loops, and a C-terminus in the cytoplasmic compartment. 2 The C-termini of these receptors contain serine and threonine residues which, on phosphorylation, are involved in signaling and receptor desensitization. 2,3 Agonistinduced phosphorylation of chemokine receptors, such as CCR5, can result in homologous desensitization and internalization of the receptors. 4,5 Chemokine receptors may also be subjected to "heterologous desensitization" when the cells are activated by agonists selective for unrelated STM receptors. 3 For example, activation of formyl peptide receptor (FPR), the receptor for the bacterial chemotactic peptide fMLF, effectively desensitizes a number of chemoattractant receptors, including the receptors for the chemokine interleukin (IL) 8. 3 Both homologous and heterologous desensitization results in impairment of various biologic functions of chemokine receptors in response to further stimulation by their cognate ligands. 3 Because human leukocytes express a variety of chemoattractant receptors, the "cross-talk" among those receptors has been proposed to be important in fine-tuning of cell responses in the presence of multiple stimulants.Two STM receptors that can be activated by the bacterial chemotactic peptide fMLF have been identified and cloned. 6,7 FPR interacts with low concentrations of fMLF and thus acts as a high-affinity fMLF receptor. On the other hand, the low-affinity variant receptor formyl peptide receptor-like 1 (FPRL1) exhibits Ca ϩϩ flux only in response to high concentrations of fMLF. 6,7 Despite the fact that both FPR and FPRL1 are among the earliest chemoattractant receptors discovered on human phagocytic leukocytes, their biologic significance in host defense and immune responses is not clear. Although the nature of the host-derived ligands for FPR remains obscure, at least 2 endogenous molecules in humans, the lipid metabolite lipoxin A4 (LXA4) 8 and a chemotactic acute-phase protein serum amyloid A (SAA), 9 have been found to activate FPRL1. HIV-1 envelope glycoprotein gp120 and gp41 also contain domains that preferentially activate either FPR or FPRL1. ...