Interleukin (IL)-15 and IL-2 reciprocally regulate expression of the chemokine receptor CX3CR1 through selective NFAT1- and NFAT2-dependent mechanisms.

We have recently reported that interleukin (IL)-15 and IL-2, which signal through IL-2Rbetagamma, oppositely regulate expression of the proinflammatory chemokine receptor CX3CR1. Here we delineate molecular mechanisms responsible for this paradox. By using a luciferase reporter plasmid, we identified a 433-bp region spanning the major transcriptional start point of human CX3CR1 that, when expressed in human peripheral blood mononuclear cells (PBMCs), possessed strong constitutive promoter activity. IL-2 and IL-15 treatment increased and abolished this activity, respectively, mimicking their effects on endogenous CX3CR1. IL-2 and IL-15 have been reported to also have opposite effects on the immunoregulatory transcription factor NFAT (nuclear factor of activated T cells), and the 433-bp region contains a kappaB-like NFAT site. The effects of IL-15 and IL-2 on both CX3CR1 reporter activity and endogenous CX3CR1 transcription in PBMCs were abolished by the NFAT inhibitors cyclosporin A and VIVIT. Moreover, mutation of the kappaB-like NFAT sequence markedly attenuated IL-2 and IL-15 modulation of CX3CR1 promoter-reporter activity in PBMCs. Furthermore, chromatin immunoprecipitation revealed that IL-15 promoted specific recruitment of NFAT1 but not NFAT2 to the CX3CR1 promoter, whereas IL-2 had the converse effect. This appears to be relevant in vivo because mouse CX3CR1 mRNA was expressed in both PBMCs and splenocytes from NFAT1-/- mice injected with recombinant IL-15 but was undetectable in cells from IL-15-injected NFAT1+/+ BALB/c mice; as predicted, IL-2 up-regulated cx3cr1 in both mouse strains to a similar extent. Thus, by pharmacologic, genetic, and biochemical criteria in vitro and in vivo, our results suggest that IL-15 and IL-2 oppositely regulate CX3CR1 gene expression by differentially recruiting NFAT1 and NFAT2 to a kappaB-like NFAT site within the CX3CR1 promoter. We propose that expression of CX3CR1 and possibly other immunoregulatory genes may be determined in part by the balance of NFAT1 and NFAT2 activity in leukocytes.

Chemokine receptor mutant CX3CR1-M280 has impaired adhesive function and correlates with protection from cardiovascular disease in humans.

The chemokine receptor CX3CR1 is a proinflammatory leukocyte receptor specific for the chemokine fractalkine (FKN or CX3CL1). In two retrospective studies, CX3CR1 has been implicated in the pathogenesis of atherosclerotic cardiovascular disease (CVD) based on statistical association of a common receptor variant named CX3CR1-M280 with lower prevalence of atherosclerosis, coronary endothelial dysfunction, and acute coronary syndromes. However, the general significance of CX3CR1-M280 and its putative mechanism of action have not previously been defined. Here we show that FKN-dependent cell-cell adhesion under conditions of physiologic shear is severely reduced in cells expressing CX3CR1-M280. This was associated with marked reduction in the kinetics of FKN binding as well as reduced FKN-induced chemotaxis of primary leukocytes from donors homozygous for CX3CR1-M280. We also show that CX3CR1-M280 is independently associated with a lower risk of CVD (adjusted odds ratio, 0.60, P = 0.008) in the Offspring Cohort of the Framingham Heart Study, a long-term prospective study of the risks and natural history of this disease. These data provide mechanism-based and consistent epidemiologic evidence that CX3CR1 may be involved in the pathogenesis of CVD in humans, possibly by supporting leukocyte entry into the coronary artery wall. Moreover, they suggest that CX3CR1-M280 is a genetic risk factor for CVD.

Associations of chemokine system polymorphisms with clinical outcomes and treatment responses of chronic hepatitis C.

BACKGROUND & AIMS: CCR5Delta32, a 32-base pair deletion of the CC chemokine receptor (CCR) 5 gene, is associated with slowed human immunodeficiency virus disease progression in heterozygotes and protection against infection in homozygotes. A recent study found a higher than expected frequency of CCR5Delta32/Delta32 in patients with hepatitis C virus infection. The roles of other disease-associated chemokine system polymorphisms have not been evaluated in hepatitis C virus infection. METHODS: Six chemokine system polymorphisms (CCR5Delta32, CCR5 promoter 59029-G/A, CCR2 -64I, RANTES [regulated upon activation, normal T cells expressed and secreted] -403 -G/A, and -28 -C/G and stromal derived factor 1 -3'A) were studied in 417 patients with liver diseases (339 with hepatitis C) and 2380 blood donors. The clinical parameters of hepatitis C virus infection were compared between carriers and noncarriers of each genetic variant. RESULTS: The frequency of CCR5Delta32 homozygosity was 0.8% in whites with hepatitis C virus and 1.1% in controls (P = 0.75). The CCR5Delta32 allele was not associated with any of the clinical parameters of hepatitis C virus infection. Hepatitis C virus-seropositive whites with the RANTES -403-A allele were less likely to have severe hepatic inflammation compared with those without (odds ratio, 0.34; P = 0.03). In multivariate analysis, the CCR5 promoter 59029 -A allele was marginally associated with a sustained response to interferon therapy (odds ratio, 3.07; P = 0.048). CONCLUSIONS: In this cohort, the frequency of CCR5Delta32 homozygosity in patients with hepatitis C was similar to controls. The high prevalence of CCR5Delta32 homozygosity in the hepatitis C virus patients of the earlier study likely reflects resistance to human immunodeficiency virus infection in hemophiliacs rather than a susceptibility to hepatitis C virus infection. Expression of CCR5 and RANTES may be important in the modulation of hepatic inflammation and response to interferon therapy in chronic hepatitis C.