The chemokine CXC ligand 8 (CXCL8)͞IL-8 and related agonists recruit and activate polymorphonuclear cells by binding the CXC chemokine receptor 1 (CXCR1) and CXCR2. Here we characterize the unique mode of action of a small-molecule inhibitor (Repertaxin) of CXCR1 and CXCR2. Structural and biochemical data are consistent with a noncompetitive allosteric mode of interaction between CXCR1 and Repertaxin, which, by locking CXCR1 in an inactive conformation, prevents signaling. Repertaxin is an effective inhibitor of polymorphonuclear cell recruitment in vivo and protects organs against reperfusion injury. Targeting the Repertaxin interaction site of CXCR1 represents a general strategy to modulate the activity of chemoattractant receptors. L eukocyte trafficking into tissue sites of inflammation is directed by chemokines. Chemokines are grouped into four families based on a cysteine motif in the amino terminus of the protein (1, 2). Human CXC ligand 8 (CXCL8)͞IL-8 and related molecules are polymorphonuclear cells (PMN) chemoattractants. Two high-affinity human CXCL8 receptors are known, CXC chemokine receptor 1 (CXCR1) and CXC chemokine receptor 2 (CXCR2). Only one corresponding receptor has been identified in the mouse, and this is recognized by ligands that act as neutrophil attractant, although a mouse orthologue of CXCL8 has not been identified. By recruiting and activating PMN, CXCL8 and related rodent molecules have been implicated in a wide range of disease states characterized by PMN infiltration in organs, including reperfusion injury (RI) (3).G protein-coupled receptors (GPCR) are a prime target for the development of new strategies to control diverse pathologies (4-6). Antichemokine strategies include antibodies, N-terminal modified chemokines, and small-molecule antagonists (7-9). Here we describe a class of GPCR inhibitors that specifically block the inflammatory CXCL8 chemokine receptors CXCR1 and CXCR2 by means of an allosteric noncompetitive mode of interaction and protection against RI. Materials and MethodsReagents. Repertaxin (R)(Ϫ)-2-(4-isobutylphenyl)propionyl methansulfonamide) salified with L-lysine was dissolved in saline. Chemokines were from PeproTech (London). Chemicals, cell culture reagents, and protease inhibitors were from Sigma.Migration. Cell migration of human PMN and monocytes and rodent peritoneal PMN were evaluated in a 48-well microchemotaxis chamber with or without Repertaxin. Agonists (1 nM CXCL8, 10 nM N-formyl-L-methionyl-L-leucyl-L-phenylalanine (fMLP), 10 nM CXCL1, 2.5 nM CCL2, 1 nM C5a, 5 nM rat and mouse CXCL1, and 2.5 nM rat and mouse CXCL2) were seeded in the lower compartment. The chemotaxis chamber was incubated for 45 min (human PMN), 1 h (rodent PMN), or 2 h (monocytes). L1.2 migration was evaluated by using 5-m pore-size Transwell filters (Costar) (10). Mutation Analysis of CXCR1 and Signaling. The human CXCR1 ORF was PCR amplified from a CXCR1͞pCEP4 plasmid (kindly provided by P. M. Murphy, National Institutes of Health, Bethesda). Receptor mutants and chimeric re...

Increasing evidence suggests that a continuous release of histamine from mast cells occurs in the airways of asthmatic patients and that histamine may modulate functions of other inflammatory cells such as macrophages. In the present study histamine (10−9–10−6 M) increased in a concentration-dependent fashion the basal release of β-glucuronidase (EC50 = 8.2 ± 3.5 × 10−9 M) and IL-6 (EC50 = 9.3 ± 2.9 × 10−8 M) from human lung macrophages. Enhancement of β-glucuronidase release induced by histamine was evident after 30 min and peaked at 90 min, whereas that of IL-6 required 2–6 h of incubation. These effects were reproduced by the H1 agonist (6-[2-(4-imidazolyl)ethylamino]-N-(4-trifluoromethylphenyl)heptane carboxamide but not by the H2 agonist dimaprit. Furthermore, histamine induced a concentration-dependent increase of intracellular Ca2+ concentrations ([Ca2+]i) that followed three types of response, one characterized by a rapid increase, a second in which [Ca2+]i displays a slow but progressive increase, and a third characterized by an oscillatory pattern. Histamine-induced β-glucuronidase and IL-6 release and [Ca2+]i elevation were inhibited by the selective H1 antagonist fexofenadine (10−7–10−4 M), but not by the H2 antagonist ranitidine. Inhibition of histamine-induced β-glucuronidase and IL-6 release by fexofenadine was concentration dependent and displayed the characteristics of a competitive antagonism (Kd = 89 nM). These data demonstrate that histamine induces exocytosis and IL-6 production from human macrophages by activating H1 receptor and by increasing [Ca2+]i and they suggest that histamine may play a relevant role in the long-term sustainment of allergic inflammation in the airways.

Secretory phospholipases A2 (sPLA2s) are a group of extracellular enzymes that release fatty acids at the sn-2 position of phospholipids. Group IIA sPLA2 has been detected in inflammatory fluids, and its plasma level is increased in inflammatory diseases. To investigate a potential mechanism of sPLA2-induced inflammation we studied the effect of group IA (from cobra venom) and group IIA (human synovial) sPLA2s on human macrophages. Both sPLA2s induced a concentration- and Ca2+-dependent, noncytotoxic release of β-glucuronidase (16.2 ± 2.4% and 13.1 ± 1.5% of the total content with groups IA and IIA, respectively). Both sPLA2s also increased the rate of secretion of IL-6 and enhanced the expression of IL-6 mRNA. Preincubation of macrophages with inhibitors of the hydrolytic activity of sPLA2 or cytosolic PLA2 did not influence the release of β-glucuronidase. Incubation of macrophages with p-aminophenyl-mannopyranoside-BSA (mp-BSA), a ligand of the mannose receptor, also resulted in β-glucuronidase release. However, while preincubation of macrophages with mp-BSA had no effect on β-glucuronidase release induced by group IIA sPLA2, it enhanced that induced by group IA sPLA2. A blocking Ab anti-mannose receptor inhibited both mp-BSA- and group IIA-induced β-glucuronidase release. Taken together, these data indicate that group IA and IIA sPLA2s activate macrophages with a mechanism independent from their enzymatic activities and probably related to the activation of the mannose receptor or sPLA2-specific receptors. The secretion of enzymes and cytokines induced by sPLA2s from human macrophages may play an important role in inflammation and tissue damage associated with the release of sPLA2s.

A multicenter analysis of 57 consecutive human immunodeficiency virus-positive patients with progressive multifocal leukoencephalopathy (PML) was performed, to identify correlates of longer survival. JC virus (JCV) DNA was quantified in the cerebrospinal fluid (CSF) by polymerase chain reaction. Two months after therapy, 4% of the patients without highly active antiretroviral therapy (HAART) and 26% with HAART showed neurologic improvement or stability (P=.03), and 8% and 57%, respectively, reached undetectable JCV DNA levels in the CSF (P=.04). One-year probability of survival was.04 without HAART and.46 with HAART. HAART and lack of neurologic progression 2 months after diagnosis were independently associated with longer survival. Among HAART-treated patients, a baseline JCV DNA <4.7 log, and reaching undetectable levels after therapy predicted longer survival. Survival of AIDS-related PML is improved by HAART when JCV replication is controlled.

Secretory phospholipases A2 (sPLA2) are released in the blood of patients with various inflammatory diseases and exert proinflammatory activities by releasing arachidonic acid (AA), the precursor of eicosanoids. We examined the ability of four sPLA2 to activate blood and synovial fluid monocytes in vitro. Monocytes were purified from blood of healthy donors or from synovial fluid of patients with rheumatoid arthritis by negative immunoselection and by adherence to plastic dishes, respectively. The cells were incubated with group IA, IB, IIA and III sPLA2 and the release of TNF‐α, IL‐6 and IL‐12 was determined by ELISA. Group IA, IB and IIA sPLA2 induced a concentration‐dependent release of TNF‐α and IL‐6 from bloodmonocytes. These sPLA2 activated IL‐12 production only in monocytes preincubated with IFN‐γ. Group IA and IIA sPLA2 also induced TNF‐α and IL‐6 release from synovial fluid monocytes. TNF‐α and IL‐6 release paralleled an increase in their mRNA expression and was independent from the capacity of sPLA2 to mobilize AA. These results indicate that sPLA2 stimulate cytokine release from blood and synovial fluid monocytes by a mechanism at least partially unrelated to their enzymatic activity. This effect may concur with the generation of AA in theproinflammatory activity of sPLA2 released during inflammatory diseases.