mdr1a-encoded P-glycoprotein is not required for peripheral T cell proliferation, cytokine release, or cytotoxic effector function in mice.

The plasma membrane transport protein P-glycoprotein (P-gp) is expressed by subsets of both CD4+ and CD8+ T cells in mice. The proportion of T cells that express P-gp goes up with age, and the P-gp-expressing subset of the CD4 memory population is hyporesponsive in many in vitro assays. The significance of P-gp expression for T cell function has not been well established, although several reports have suggested that it may promote cytokine export and/or cytotoxic T cell function. To elucidate which T cell functions may require P-gp, we have compared a variety of responses using T cells from wt and P-gp knockout mice. Protein expression and rhodamine-123 efflux studies revealed that peripheral T cells exclusively utilize the mdr1a-encoded isoform rather than the homologous mdr1b or mdr2 isoforms. Comparisons of T cells from mdr1a+/+ and mdr1a-/- mice showed no differences in proliferation or in secretion of IL-2, IL-4, IL-5, IL-10, or IFN-gamma in response to polyclonal stimulation. Moreover, mdr1a-/- T cells produced strong allospecific cytotoxic responses comparable to those of wt T cells. Our results show that P-gp is not a necessary component of peripheral T cell functional responses. Further investigation will be needed to determine the significance of P-gp expression in T lymphocytes.     

MDR1A (ABCB1)-deficient CF-1 mutant mice are susceptible to cerebral malaria induced by Plasmodium berghei ANKA

Under experimental conditions, Plasmodium berghei infection causes cerebral malaria (CM) in susceptible strains of mice such as C57BL/6 and CBA/Ca, whereas BALB/c or DBA/2J strains serve as a model for CM-resistant mice. The aim of the present study was to investigate the susceptibility of the CF1 mouse strain, carrying a spontaneous mutation of the mdr1a gene, to infection with Plasmodium berghei ANKA (PbA). The mdr1a gene codes for P-glycoprotein (P-gp/ABCB1), an efflux pump that is one of the major components of the blood-brain barrier. P-gp effluxes a broad range of xenobiotics from the brain to blood, preventing accumulation and toxicity in the central nervous system. CFI mdr1a (-/-) mice are used to investigate drug transport by efflux pumps. Because many antimalarial agents are effluxed by P-gp (mefloquine, quinine), it was important to determine whether CF1 mice can develop cerebral malaria to predict drug toxicity during cerebral malaria. Our work showed that CF1 mdr1a (-/-) mice are susceptible to PbA. CF1 and C57BL/6N mice (the reference strain) infected with PbA have similar profiles with regard to clinical signs, brain histological lesions, and brain macrophagic activation observed by immunohistological methods.     

Murine P-glycoprotein Deficiency Alters Intestinal Injury Repair and Blunts Lipopolysaccharide-Induced Radioprotection

P-glycoprotein (P-gp) has been reported to increase stem cell proliferation and regulate apoptosis. Absence of P-gp results in decreased repair of intestinal epithelial cells after chemical injury. To further explore the mechanisms involved in the effects of P-gp on intestinal injury and repair, we used the well-characterized radiation injury model. In this model, injury repair is mediated by production of prostaglandins (PGE(2)) and lipopolysaccharide (LPS) has been shown to confer radioprotection. B6.mdr1a(-/-) mice and wild-type controls were subjected to 12 Gy total body X-ray irradiation and surviving crypts in the proximal jejunum and distal colon were evaluated 3.5 days after irradiation. B6.mdr1a(-/-) mice exhibited normal baseline stem cell proliferation and COX dependent crypt regeneration after irradiation. However, radiation induced apoptosis was increased and LPS-induced radioprotection was blunted in the C57BL6.mdr1a(-/-) distal colon, compared to B6 wild-type controls. The LPS treatment induced gene expression of the radioprotective cytokine IL-1α, in B6 wild-type controls but not in B6.mdr1a(-/-) animals. Lipopolysaccharid-induced radioprotection was absent in IL-1R1(-/-) animals, indicating a role for IL-1α in radioprotection, and demonstrating that P-gp deficiency interferes with IL-1α gene expression in response to systemic exposure to LPS.     

IL-18 contributes to host resistance against infection with Pseudomonas aeruginosa through induction of IFN-gamma production

Pseudomonas aeruginosa keratitis destroys the cornea in susceptible (B6), but not resistant (BALB/c) mice. To determine mechanisms mediating resistance, the role of IFN-gamma, IL-12, and IL-18 was tested in BALB/c mice. RT-PCR analysis detected IFN-gamma mRNA expression levels in cornea that were significantly increased at 1-7 days postinfection. IL-18 mRNA was detected constitutively in cornea and, at 1-7 days postinfection, levels were elevated significantly, while no IL-12 mRNA was similarly detected. To test whether IL-18 contributed to IFN-gamma production, mice were treated with anti-IL-18 mAb. Treatment decreased corneal IFN-gamma mRNA levels, and bacterial load and disease increased/worsened, compared with IgG-treated mice. To stringently examine the role of IFN-gamma in bacterial killing, knockout (-/-) vs wild-type (wt) mice also were tested. All corneas perforated, and bacterial load was increased significantly in -/- vs wt mice. Because disease severity was increased in IFN-gamma(-/-) vs IL-18-neutralized mice, and since IL-18 also induces production of TNF, we tested for TNF-alpha in both groups. ELISA analysis demonstrated significantly elevated corneal TNF-alpha protein levels in IFN-gamma(-/-) vs wt mice after infection. In contrast, RT-PCR analysis of IL-18-neutralized vs IgG-treated infected mice revealed decreased corneal TNF-alpha mRNA expression. Next, to resolve whether TNF was required for bacterial killing, TNF-alpha was neutralized in BALB/c mice. No difference in corneal bacterial load was detected in neutralized vs IgG-treated mice. These data provide evidence that IL-18 contributes to the resistance response by induction of IFN-gamma and that IFN-gamma is required for bacterial killing.     

Dynamics of multidrug resistance: P-glycoprotein analyses with positron emission tomography

Multidrug resistance (MDR) is characterized by the occurrence of cross-resistance to a broad range of structurally and functionally unrelated drugs. Several mechanisms are involved in MDR. One of the most well-known mechanisms is the overexpression of P-glycoprotein (P-gp), encoded by the MDR1 gene in humans and by the mdr1a and mdr1b genes in rodents. P-gp is extensively expressed in the human body, e.g., in the blood-brain barrier and also in solid tumor tissue. Overexpression of P-gp on tumor membranes might result in MDR of human tumors. To circumvent this resistant phenotype, several P-gp modulators such as cyclosporin A (CsA) are available. Competition between P-gp drugs and modulators results in decreased transport of the drug out of tumor tissue and an increased cellular level of these drugs. For effective clinical treatment it is important to have knowledge about P-gp functionality in tumors. Therefore, we have developed a method to measure the P-gp functionality in vivo with PET and [(11)C]verapamil as a positron-emitting P-gp substrate. The results obtained in rodents and in cancer patients are described in this article.     

Role of immunity in age-related resistance to paralysis after murine leukemia virus infection.

Resistance to the paralytic effects of a wild mouse (Cas-Br-M) murine leukemia virus infection develops with age and is complete by 10 days of age in susceptible NFS mice. The possibility that cell-mediated immunity plays a significant role in this resistance was suggested by the observation that treatment of 10-day-old mice with antithymocyte serum rendered them susceptible to paralysis. By comparison, mice rendered incapable of generating a humoral immune response by treatment from birth to 1 month of age with anti-immunoglobulin M serum did not develop paralysis after challenge with virus at day 10. Transfer of unseparated and T-cell-enriched populations of Cas-Br-M murine leukemia virus-immune spleen cells protected neonatally infected NFS recipients from paralysis; transfer of Cas-Br-M murine leukemia virus-immune populations enriched for B cells delayed the onset but did not ultimately protect neonatally infected NFS mice from paralysis. Transfer of naive adult spleen cells had no protective effect in neonatally infected NFS mice. High-level virus replication occurred in the spleens and brains of all mice that developed paralysis regardless of treatment; low-level virus replication in spleen and barely detectable replication in brain occurred in mice that remained clinically normal. These studies suggest that the age-acquired resistance to the paralytic effect of Cas-Br-M murine leukemia virus infection is immunologically mediated and that T cells may play a major role.     

Antinociceptive effects of morphine-6-glucuronide in homozygous MDR1a P-glycoprotein knockout and in wildtype mice in the hotplate test

Morphine-6-glucuronide (M6G), a major metabolite of morphine with agonist opioid-receptor activity, was reported to be a substrate of P-glycoprotein (P-gp). Inhibition of P-gp may thus result in higher brain uptake of M6G. The goal of this observer-blinded, placebo controlled study, was to compare the antinociceptive effects of M6G in homozygous P-gp knockout (mdr1a(-/-)) and wildtype (mdr1a(+/+)) mice. M6G was injected intraperitoneally as a single dose of 0, 0.5, 1, 2.5, 5, and 10 mg/kg. Eight P-gp knockout and eight wildtype mice were studied per dose. A hot plate test was performed before and 5, 15, 30, 60, 90, 120, and 150 min after M6G administration. Plasma-concentrations of M6G, morphine, and morphine-3-glucuronide (M3G) were measured after intraperitoneal injection of 5 mg/kg M6G in another 14 P-gp knockout and 14 wildtype mice. No difference neither in the dose response relationship, nor in the time course of response latency times were observed between P-gp knockout and wildtype mice. However, latency times increased with higher doses of M6G, with antinociception significantly different from placebo at a M6G dose of 5 and 10 mg/kg. P-gp knockout mice tended to have higher plasma concentrations than the wildtype. However, plasma concentrations widely overlapped between groups and therefore no statistical significant group difference could be detected. We conclude that despite reported doubling of M6G brain uptake, absence of mdr1a coded P-gp does not enhance antinociceptive effects of M6G in the hotplate test after acute single-dose administration in mdr1a(-/-) knockout mice.     

Antibody prevents virus reactivation within the central nervous system.

The neurotropic JHM strain of mouse hepatitis virus (JHMV) produces an acute CNS infection characterized by encephalomyelitis and demyelination. The immune response cannot completely eliminate virus, resulting in persistence associated with chronic ongoing CNS demyelination. The contribution of humoral immunity to viral clearance and persistent infection was investigated in mice homozygous for disruption of the Ig mu gene (IgM-/-). Acute disease developed with equal kinetics and severity in IgM-/- and syngeneic C57BL/6 (wt) mice. However, clinical disease progressed in IgM-/- mice, while wt mice recovered. Viral clearance during acute infection was similar in both groups, supporting a primary role of cell-mediated immunity in viral clearance. In contrast to wt mice, in which infectious virus was reduced to below detection following acute infection, increasing infectious virus was recovered from the CNS of the IgM-/- mice following initial clearance. No evidence was obtained for selection of variant viruses nor was there an apparent loss of cell-mediated immunity in the absence of Ab. Passive transfer of anti-JHMV Ab following initial clearance prevented reactivation of infectious virus within the CNS of IgM-/- mice. These data demonstrate the clearance of infectious virus during acute disease by cell-mediated immunity. However, immunologic control is not maintained in the absence of anti-viral Ab, resulting in recrudescence of infectious virus. These data suggest that humoral immunity plays no role in controlling virus during acute infection, but plays an important role in establishing and maintaining CNS viral persistence.     

The murine double-stranded RNA-dependent protein kinase PKR is required for resistance to vesicular stomatitis virus

Interferon (IFN)-induced antiviral responses are mediated through a variety of proteins, including the double-stranded RNA-dependent protein kinase PKR. Here we show that fibroblasts derived from PKR(-/-) mice are more permissive for vesicular stomatitis virus (VSV) infection than are wild-type fibroblasts and demonstrate a deficiency in alpha/beta-IFN-mediated protection. We further show that mice lacking PKR are extremely susceptible to intranasal VSV infection, succumbing within days after instillation with as few as 50 infectious viral particles. Again, alpha/beta-IFN was unable to rescue PKR(-/-) mice from VSV infection. Surprisingly, intranasally infected PKR(-/-) mice died not from pathology of the central nervous system but rather from acute infection of the respiratory tract, demonstrating high virus titers in the lungs compared to similarly infected wild-type animals. These results confirm the role of PKR as the major component of IFN-mediated resistance to VSV infection. Since previous reports have shown PKR to be nonessential for survival in animals challenged with encephalomyocarditis virus, influenza virus, and vaccinia virus (N. Abraham et al., J. Biol. Chem. 274:5953-5962, 1999; Y. Yang et al., EMBO J. 14:6095-6106, 1995), our findings serve to highlight the premise that host dependence on the various mediators of IFN-induced antiviral defenses is pathogen specific.     

Puromycin selectively increases mdr1a expression in immortalized rat brain endothelial cell lines

The blood-brain barrier (BBB) plays an important role in controlling the passage of molecules from blood to brain extracellular fluid. The multidrug efflux pump P-glycoprotein (P-gp) is highly expressed in the luminal membrane of brain endothelium and contributes to the formation of a functional barrier to lipid-soluble drugs such as anticancer agents. The mdr1a P-gp-encoding gene is exclusively expressed in the rodent BBB. Primary cultures of rat brain endothelial cells and GP8.3 cells showed a dramatic decrease in mdr1a mRNA level and some expression of mdr1b mRNA. GPNT cells, derived from GP8.3 cells after transfection with a puromycin resistance gene, were chronically treated with 5 microg/mL puromycin, a P-gp substrate. Compared with rat brain endothelial cells and GP8.3 cells, GPNT cells exhibited a very high level of expression of mdr1a mRNA together with a moderate level of mdr1b mRNA expression. Accordingly, P-gp expression and activity were strongly increased. When GP8.3 and puromycin-starved GPNT cells were treated with puromycin, mdr1a expression was selectively increased. High expression of mdr1a mRNA in GPNT cells may thus be related to the chronic treatment with puromycin. We conclude that GPNT cells may be used as a valuable rat in vitro model for studying the regulation of mdr1a expression at the BBB level.     

Chromosomal locations and gonadal dependence of genes that mediate resistance to ectromelia (mousepox) virus-induced mortality.

Four genetic loci were tested for linkage with loci that control genetic resistance to lethal ectromelia virus infection in mice. Three of the loci were selected because of concordance with genotypes assigned to recombinant inbred (RI) strains of mice derived from resistant C57BL/6 and susceptible DBA/2 (BXD) mice on the basis of their responses to challenge infection. Thirty-six of 167 male (C57BL/6 x DBA/2)F1 x DBA/2 backcross (BC) mice died (22%), of which 27 (75%) were homozygous for DBA/2 alleles at Hc and H-2D. Twenty-eight percent of sham-castrated and 6% of sham-ovariectomized BC mice were susceptible to lethal mousepox, whereas 50% of gonadectomized mice were susceptible. There was no linkage evident between Hc or H-2D and loci that controlled resistance to lethal ectromelia virus infection in 44 castrated BC mice. Mortality among female mice of BXD RI strains with susceptible or intermediate male phenotypes was strongly correlated (r = 0.834) with male mortality. Gonadectomized C57BL/6 mice were as resistant as intact mice to lethal ectromelia virus infection. These results indicate that two gonad-dependent genes on chromosomes 2 and 17 and one gonad-independent gene control resistance to mousepox virus infection, that males and females share gonad-dependent genes, and that the gonad-independent gene is fully protective.     

The multidrug resistance P-glycoprotein modulates cell regulatory volume decrease.

Cell volume is frequently down-regulated by the activation of anion channels. The role of cell swelling-activated chloride channels in cell volume regulation has been studied using the patch-clamp technique and a non-invasive microspectrofluorimetric assay for changes in cell volume. The rate of activation of these chloride channels was shown to limit the rate of regulatory volume decrease (RVD) in response to hyposmotic solutions. Expression of the human MDR1 or mouse mdr1a genes, but not the mouse mdr1b gene, encoding the multidrug resistance P-glycoprotein (P-gp), increased the rate of channel activation and the rate of RVD. In addition, P-gp decreased the magnitude of hyposmotic shock required to activate the channels and to elicit RVD. Tamoxifen selectively inhibited both chloride channel activity and RVD. No effect on potassium channel activity was elicited by expression of P-gp. The data show that, in these cell types, swelling-activated chloride channels have a central role in RVD. Moreover, they clarify the role of P-gp in channel activation and provide direct evidence that P-gp, through its effect on chloride channel activation, enhances the ability of cells to down-regulate their volume.     

Type I IFNs play a role in early resistance, but subsequent susceptibility, to the African trypanosomes

Macrophages express a spectrum of proinflammatory and regulatory mediators during African trypanosomiasis. Microarray analyses revealed similar profiles of induced genes in macrophages stimulated with the trypanosome soluble variant surface glycoprotein in vitro and in macrophages taken from infected mice. Genes associated with the acute phase response and with type I IFN responses were prominent components of the macrophage activation profiles expressed within 72 h in vitro and in vivo. Thus, induction of proinflammatory gene expression is a characteristic of early trypanosome infection that is driven primarily by soluble variant surface glycoprotein exposure, and it may be that IFN-alpha/beta plays a central role in regulation of early resistance to trypanosomes. To test this hypothesis, we assessed parameters of infection in mouse strains with genetic alterations in the IFN-alpha/beta response pathway. We found that Ifnar1(-/-) mice, which lack the receptor for type I IFNs, exhibited delayed control of parasite burden during the first week of infection and died earlier than did wild-type controls. However, infection of Ubp43(-/-) mice, which are hyperresponsive to type I IFNs, did not exhibit enhanced resistance to trypanosomes. Instead, these animals also failed to control parasite burden and were more susceptible than wild-type animals. Additionally, the Ubp43(-/-) mice exhibited a significant defect in IFN-gamma production, which is definitively linked to host resistance in trypanosomiasis. These results show that type I IFNs play a role in early control of parasites in infected mice but may contribute to down-regulation of IFN-gamma production and subsequent loss of host resistance later in infection.     

Effect of macrophage blockade on the resistance of inbred mice toParacoccidioides brasiliensis infection

The effect of macrophage blockade on the natural resistance and on the adaptative immune response of susceptible (B10.D2/oSn) and resistant (A/Sn) mice toParacoccidioides brasiliensis infection was investigated. B10.D2/oSn and A/Sn mice previously injected with colloidal carbon were infected ip with yeast cells to determine the 50% lethal dose, and to evaluate the anatomy and histopathology, macrophage activation, antibody production and DTH reactions. Macrophage blockade rendered both resistant and susceptible mice considerably more susceptible to infection, as evidenced by increased mortality and many disseminated lesions.P. brasiliensis infection and/or carbon treatment increased the ability of macrophages from resistant mice to spread up to 25 days after treatment. In susceptible mice the enhanced spreading capacity induced by carbon treatment was impaired at all assayed periods except at 1 week after infection. Macrophage blockade enhanced DTH reactions in resistant mice, but did not alter these reactions in susceptible mice, which remained anergic. To the contrary, macrophage blockade enhanced specific antibody production by susceptible mice, but did not affect the low levels produced by resistant mice. The effect of macrophage blockade confirms the natural tendency of resistant animals to mount DTH reactions in the course of the disease and the preferential antibody response developed by susceptible mice afterP. brasiliensis infection. On the whole, macrophage functions appear to play a fundamental role in the natural and acquired resistance mechanisms toP. brasiliensis infection.     

Genetically determined resistance to murine cytomegalovirus and herpes simplex virus in newborn mice.

Mice which were infected with the herpesvirus murine cytomegalovirus or herpes simplex virus type 1 on the day of birth exhibited mouse strain-dependent differences in the development of lethal disease. The pattern of resistance among the strains was distinct for each virus and closely resembled that reported in adult mice. However, much lower doses of the viruses were required in newborn mice to reveal these resistance patterns. For murine cytomegalovirus, both H-2-associated and non-H-2 genes conferred resistance, and, as has been shown for adults, there was a 25-fold difference in the dose required to kill 50% of the animals belonging to the most resistant and susceptible strains. The resistance of newborn mice to herpes simplex virus type 1 was conferred by non-H-2 genes in C57BL/6 mice, as has been reported for adults, and newborn C57BL/6 mice were considerably more resistant than mice of susceptible strains. Resistance was also reflected in the titer of these viruses in the spleen or liver early in infection and, with murine cytomegalovirus, in the survival time of infected mice. The resistance of newborn mice to lethal disease was not conferred postnatally by the mother. This appears to be the first report of genetically determined resistance to herpesviruses in newborn mice. Such autonomous virus-specific resistance may provide a significant barrier to naturally acquired infection in genetically resistant strains. Similar genetically regulated mechanisms may protect the newborns of many species, including humans, against infection with herpesviruses.     

Alpha/beta interferons regulate murine gammaherpesvirus latent gene expression and reactivation from latency

Alpha/beta interferon (IFN-alpha/beta) protects the host from virus infection by inhibition of lytic virus replication in infected cells and modulation of the antiviral cell-mediated immune response. To determine whether IFN-alpha/beta also modulates the virus-host interaction during latent virus infection, we infected mice lacking the IFN-alpha/beta receptor (IFN-alpha/betaR(-/-)) and wild-type (wt; 129S2/SvPas) mice with murine gammaherpesvirus 68 (gammaHV68), a lymphotropic gamma-2-herpesvirus that establishes latent infection in B cells, macrophages, and dendritic cells. IFN-alpha/betaR(-/-) mice cleared low-dose intranasal gammaHV68 infection with wt kinetics and harbored essentially wt frequencies of latently infected cells in both peritoneum and spleen by 28 days postinfection. However, latent virus in peritoneal cells and splenocytes from IFN-alpha/betaR(-/-) mice reactivated ex vivo with >40-fold- and 5-fold-enhanced efficiency, respectively, compared to wt cells. Depletion of IFN-alpha/beta from wt mice during viral latency also significantly increased viral reactivation, demonstrating an antiviral function of IFN-alpha/beta during latency. Viral reactivation efficiency was temporally regulated in both wt and IFN-alpha/betaR(-/-) mice. The mechanism of IFN-alpha/betaR action was distinct from that of IFN-gammaR, since IFN-alpha/betaR(-/-) mice did not display persistent virus replication in vivo. Analysis of viral latent gene expression in vivo demonstrated specific upregulation of the latency-associated gene M2, which is required for efficient reactivation from latency, in IFN-alpha/betaR(-/-) splenocytes. These data demonstrate that an IFN-alpha/beta-induced pathway regulates gammaHV68 gene expression patterns during latent viral infection in vivo and that IFN-alpha/beta plays a critical role in inhibiting viral reactivation during latency.     

HIV-Tat protein induces P-glycoprotein expression in brain microvascular endothelial cells

Among the different factors which can contribute to CNS alterations associated with HIV infection, Tat protein is considered to play a critical role. Evidence indicates that Tat can contribute to brain vascular pathology through induction of endothelial cell activation. In the present study, we hypothesized that Tat can affect expression of P-glycoprotein (P-gp) in brain microvascular endothelial cells (BMEC). P-gp is an ATP-dependent cellular efflux transporter which is involved in the removal of specific non-polar molecules, including drugs used for highly active antiretroviral therapy (HAART). Treatment of BMEC with Tat(1-72) resulted in P-gp overexpression both at mRNA and protein levels. These alterations were confirmed in vivo in brain vessels of mice injected with Tat(1-72) into the hippocampus. Furthermore, pre-treatment of BMEC with SN50, a specific NF-kappaB inhibitor, protected against Tat(1-72)-stimulated expression of mdr1a gene, i.e. the gene which encodes for P-gp in rodents. Tat(1-72)-mediated changes in P-gp expression were correlated with increased rhodamine 123 efflux, indicating the up-regulation of transporter functions of P-gp. These results suggest that Tat-induced overexpression of P-gp in brain microvessels may have significant implications for the development of resistance to HAART and may be a contributing factor for low efficacy of HAART in the CNS.     

Both CXCR3 and CXCL10/IFN-inducible protein 10 are required for resistance to primary infection by dengue virus

We examined the extent to which CXCR3 mediates resistance to dengue infection. Following intracerebral infection with dengue virus, CXCR3-deficient (CXCR3(-/-)) mice showed significantly higher mortality rates than wild-type (WT) mice; moreover, surviving CXCR3(-/-) mice, but not WT mice, often developed severe hind-limb paralysis. The brains of CXCR3(-/-) mice showed higher viral loads than those of WT mice, and quantitative analysis using real-time PCR, flow cytometry, and immunohistochemistry revealed fewer T cells, CD8(+) T cells in particular, in the brains of CXCR3(-/-) mice. This suggests that recruitment of effector T cells to sites of dengue infection was diminished in CXCR3(-/-) mice, which impaired elimination of the virus from the brain and thus increased the likelihood of paralysis and/or death. These results indicate that CXCR3 plays a protective rather than an immunopathological role in dengue virus infection. In studies to identify critical CXCR3 ligands, CXCL10/IFN-inducible protein 10-deficient (CXCL10/IP-10(-/-)) mice infected with dengue virus showed a higher mortality rate than that of the CXCR3(-/-) mice. Although CXCL10/IP-10, CXCL9/monokine induced by IFN-gamma, and CXCL11/IFN-inducible T cell alpha chemoattractant share a single receptor and all three of these chemokines are induced by dengue virus infection, the latter two could not compensate for the absence of CXCL10/IP-10 in this in vivo model. Our results suggest that both CXCR3 and CXCL10/IP-10 contribute to resistance against primary dengue virus infection and that chemokines that are indistinguishable in in vitro assays differ in their activities in vivo.