Rhinoviruses A and C elicit long-lasting antibody responses with limited cross-neutralization.

Rhinoviruses (RVs) can cause severe wheezing illnesses in young children and patients with asthma. Vaccine development has been hampered by the multitude of RV types with little information about cross-neutralization. We previously showed that neutralizing antibody (nAb) responses to RV-C are detected twofold to threefold more often than those to RV-A throughout childhood. Based on those findings, we hypothesized that RV-C infections are more likely to induce either cross-neutralizing or longer-lasting antibody responses compared with RV-A infections. We pooled RV diagnostic data from multiple studies of children with respiratory illnesses and compared the expected versus observed frequencies of sequential infections with RV-A or RV-C types using log-linear regression models. We tested longitudinally collected plasma samples from children to compare the duration of RV-A versus RV-C nAb responses. Our models identified limited reciprocal cross-neutralizing relationships for RV-A (A12-A75, A12-A78, A20-A78, and A75-A78) and only one for RV-C (C2-C40). Serologic analysis using reference mouse sera and banked human plasma samples confirmed that C40 infections induced nAb responses with modest heterotypic activity against RV-C2. Mixed-effects regression modeling of longitudinal human plasma samples collected from ages 2 to 18 years demonstrated that RV-A and RV-C illnesses induced nAb responses of similar duration. These results indicate that both RV-A and RV-C nAb responses have only modest cross-reactivity that is limited to genetically similar types. Contrary to our initial hypothesis, RV-C species may include even fewer cross-neutralizing types than RV-A, whereas the duration of nAb responses during childhood is similar between the two species. The modest heterotypic responses suggest that RV vaccines must have a broad representation of prevalent types.

Enhanced Neutralizing Antibody Responses to Rhinovirus C and Age-Dependent Patterns of Infection.

Rationale: Rhinovirus (RV) C can cause asymptomatic infection and respiratory illnesses ranging from the common cold to severe wheezing.Objectives: To identify how age and other individual-level factors are associated with susceptibility to RV-C illnesses.Methods: Longitudinal data from the COAST (Childhood Origins of Asthma) birth cohort study were analyzed to determine relationships between age and RV-C infections. Neutralizing antibodies specific for RV-A and RV-C (three types each) were determined using a novel PCR-based assay. Data were pooled from 14 study cohorts in the United States, Finland, and Australia, and mixed-effects logistic regression was used to identify factors related to the proportion of RV-C versus RV-A detection.Measurements and Main Results: In COAST, RV-A and RV-C infections were similarly common in infancy, whereas RV-C was detected much less often than RV-A during both respiratory illnesses and scheduled surveillance visits (P < 0.001, χ2) in older children. The prevalence of neutralizing antibodies to RV-A or RV-C types was low (5-27%) at the age of 2 years, but by the age of 16 years, RV-C seropositivity was more prevalent (78% vs. 18% for RV-A; P < 0.0001). In the pooled analysis, the RV-C to RV-A detection ratio during illnesses was significantly related to age (P < 0.0001), CDHR3 genotype (P < 0.05), and wheezing illnesses (P < 0.05). Furthermore, certain RV types (e.g., C2, C11, A78, and A12) were consistently more virulent and prevalent over time.Conclusions: Knowledge of prevalent RV types, antibody responses, and populations at risk based on age and genetics may guide the development of vaccines or other novel therapies against this important respiratory pathogen.

Sirt3 promotes the urea cycle and fatty acid oxidation during dietary restriction.

Emerging evidence suggests that protein acetylation is a broad-ranging regulatory mechanism. Here we utilize acetyl-peptide arrays and metabolomic analyses to identify substrates of mitochondrial deacetylase Sirt3. We identified ornithine transcarbamoylase (OTC) from the urea cycle, and enzymes involved in ß-oxidation. Metabolomic analyses of fasted mice lacking Sirt3 (sirt3(-/-)) revealed alterations in ß-oxidation and the urea cycle. Biochemical analysis demonstrated that Sirt3 directly deacetylates OTC and stimulates its activity. Mice under caloric restriction (CR) increased Sirt3 protein levels, leading to deacetylation and stimulation of OTC activity. In contrast, sirt3(-/-) mice failed to deacetylate OTC in response to CR. Inability to stimulate OTC under CR led to a failure to reduce orotic acid levels, a known outcome of OTC deficiency. Thus, Sirt3 directly regulates OTC activity and promotes the urea cycle during CR, and the results suggest that under low energy input, Sirt3 modulates mitochondria by promoting amino acid catabolism and ß-oxidation.

Cadherin-related family member 3, a childhood asthma susceptibility gene product, mediates rhinovirus C binding and replication.

Members of rhinovirus C (RV-C) species are more likely to cause wheezing illnesses and asthma exacerbations compared with other rhinoviruses. The cellular receptor for these viruses was heretofore unknown. We report here that expression of human cadherin-related family member 3 (CDHR3) enables the cells normally unsusceptible to RV-C infection to support both virus binding and replication. A coding single nucleotide polymorphism (rs6967330, C529Y) was previously linked to greater cell-surface expression of CDHR3 protein, and an increased risk of wheezing illnesses and hospitalizations for childhood asthma. Compared with wild-type CDHR3, cells transfected with the CDHR3-Y529 variant had about 10-fold increases in RV-C binding and progeny yields. We developed a transduced HeLa cell line (HeLa-E8) stably expressing CDHR3-Y529 that supports RV-C propagation in vitro. Modeling of CDHR3 structure identified potential binding sites that could impact the virus surface in regions that are highly conserved among all RV-C types. Our findings identify that the asthma susceptibility gene product CDHR3 mediates RV-C entry into host cells, and suggest that rs6967330 mutation could be a risk factor for RV-C wheezing illnesses.

Effect of exogenous interferons on rhinovirus replication and airway inflammatory responses.

BACKGROUND: Human rhinoviruses (HRVs) are the most common cause of asthma exacerbations. In airway epithelial cells, the primary site of HRV infection, decreased production of interferons (IFNs) may result in greater susceptibility to HRV and worsened symptoms. Thus, exogenous IFN could supplement the innate immune response and provide a treatment for virus-induced asthma exacerbations. Furthermore, the effects of exogenous IFN could be type specific in part because of the cellular distribution of type 1 and type 2 IFN receptors. OBJECTIVE: To investigate the effects of exogenous IFNs on HRV replication in bronchial epithelial cells. METHODS: Frozen stocks of primary human bronchial epithelial cells from healthy donors were cultured in monolayers; pretreated (24 hours) with 0.1-ng/mL, 1-ng/mL, or 10-ng/mL doses of IFN-α, -ß, -λ1, or -λ2; and infected with HRV-1A. Viral replication was quantified using real-time reverse transcription-polymerase chain reaction, and cytokine and chemokine secretion 24 hours after infection was measured by multiplex enzyme-linked immunosorbent assay. RESULTS: Compared with untreated samples, IFN-α, IFN-ß, IFN-λ1, and IFN-λ2 (0.1 ng/mL) significantly reduced HRV replication after high- (P < .02) and low-dose inoculation (P < .05). Similar effects were seen in 1-ng/mL and 10-ng/mL doses of IFN, where HRV replication was significantly decreased in both high- (P < .001) and low-dose inoculation (P < .001). Treatment with IFNs also enhanced HRV-induced IFN-γ-induced protein 10 secretion (P < .001). Finally, treatment with either IFN-λ1 or IFN-λ2 significantly increased HRV-induced secretion of RANTES (regulated on activation, normal T-expressed, and presumably secreted) (P < .05) but not IL-1ß or vascular endothelial growth factor. CONCLUSION: These findings suggest that exogenous IFNs, IFN-λ1 in particular, warrant further study as a potential therapy for virus-induced asthma exacerbations.

Innate immune responses to rhinovirus are reduced by the high-affinity IgE receptor in allergic asthmatic children.

BACKGROUND: Children with allergic asthma have more frequent and severe human rhinovirus (HRV)-induced wheezing and asthma exacerbations through unclear mechanisms. OBJECTIVE: We sought to determine whether increased high-affinity IgE receptor (FcεRI) expression and cross-linking impairs innate immune responses to HRV, particularly in allergic asthmatic children. METHODS: PBMCs were obtained from 44 children, and surface expression of FcεRI on plasmacytoid dendritic cells (pDCs), myeloid dendritic cells, monocytes, and basophils was assessed by using flow cytometry. Cells were also incubated with rabbit anti-human IgE to cross-link FcεRI, followed by stimulation with HRV-16, and IFN-α and IFN-λ1 production was measured by Luminex. The relationships among FcεRI expression and cross-linking, HRV-induced IFN-α and IFN-λ1 production, and childhood allergy and asthma were subsequently analyzed. RESULTS: FcεRIα expression on pDCs was inversely associated with HRV-induced IFN-α and IFN-λ1 production. Cross-linking FcεRI before HRV stimulation further reduced PBMC IFN-α (47% relative reduction; 95% CI, 32% to 62%; P< .0001) and IFN-λ1 (81% relative reduction; 95% CI, 69% to 93%; P< .0001) secretion. Allergic asthmatic children had higher surface expression of FcεRIα on pDCs and myeloid dendritic cells when compared with that seen in nonallergic nonasthmatic children. Furthermore, after FcεRI cross-linking, allergic asthmatic children had significantly lower HRV-induced IFN responses than allergic nonasthmatic children (IFN-α, P= .004; IFN-λ1, P= .02) and nonallergic nonasthmatic children (IFN-α, P= .002; IFN-λ1, P= .01). CONCLUSIONS: Allergic asthmatic children have impaired innate immune responses to HRV that correlate with increased FcεRI expression on pDCs and are reduced by FcεRI cross-linking. These effects likely increase susceptibility to HRV-induced wheezing and asthma exacerbations.

Recent Clinical Isolates of Enterovirus D68 Have Increased Replication and Induce Enhanced Epithelial Immune Response Compared to the Prototype Fermon Strain.

In 2014, enterovirus D68 (EV-D68), previously associated primarily with mild respiratory illness, caused a large outbreak of severe respiratory illness and, in rare instances, paralysis. We compared the viral binding and replication of eight recent EV-D68 clinical isolates collected both before and during the 2014 outbreak and the prototype Fermon strain from 1962 in cultured HeLa cells and differentiated human primary bronchial epithelial cells (BEC) to understand the possible reasons for the change in virus pathogenicity. We selected pairs of closely related isolates from the same phylogenetic clade that were associated with severe vs. asymptomatic infections. We found no significant differences in binding or replication in HeLa cell cultures between the recent clinical isolates. However, in HeLa cells, Fermon had significantly greater binding (2-3 logs) and virus progeny yields (2-4 logs) but a similar level of replication (1.5-2 log increase in viral RNA from 2 h to 24 h post infection) compared to recent isolates. In differentiated BECs, Fermon and the recent EV-D68 isolates had similar levels of binding; however, the recent isolates produced 1.5-2-log higher virus progeny yields than Fermon due to increased replication. Interestingly, no significant differences in replication were identified between the pairs of genetically close recent EV-D68 clinical isolates despite the observed differences in associated disease severity. We then utilized RNA-seq to define the transcriptional responses in BECs infected with four recent EV-D68 isolates, representing major phylogenetic clades, and the Fermon strain. All the tested clinical isolates induced similar responses in BECs; however, numerous upregulated genes in antiviral and pro-inflammatory response pathways were identified when comparing the response to clinical isolates versus Fermon. These results indicate that the recent emergence in severe EV-D68 cases could be explained by an increased replication efficiency and enhanced inflammatory response induced by newly emerged clinical isolates; however, host factors are likely the main determinants of illness severity.

Structure and biochemical functions of SIRT6.

SIRT6 is a member of the evolutionarily conserved sirtuin family of NAD(+)-dependent protein deacetylases and functions in genomic stability and transcriptional control of glucose metabolism. Early reports suggested that SIRT6 performs ADP-ribosylation, whereas more recent studies have suggested that SIRT6 functions mainly as a histone deacetylase. Thus, the molecular functions of SIRT6 remain uncertain. Here, we perform biochemical, kinetic, and structural studies to provide new mechanistic insight into the functions of SIRT6. Utilizing three different assays, we provide biochemical and kinetic evidence that SIRT6-dependent histone deacetylation produces O-acetyl-ADP-ribose but at a rate ∼1,000 times slower than other highly active sirtuins. To understand the molecular basis for such low deacetylase activity, we solved the first crystal structures of this class IV sirtuin in complex with ADP-ribose and the non-hydrolyzable analog of O-acetyl-ADP-ribose, 2'-N-acetyl-ADP-ribose. The structures revealed unique features of human SIRT6, including a splayed zinc-binding domain and the absence of a helix bundle that in other sirtuin structures connects the zinc-binding motif and Rossmann fold domain. SIRT6 also lacks the conserved, highly flexible, NAD(+)-binding loop and instead contains a stable single helix. These differences led us to hypothesize that SIRT6, unlike all other studied sirtuins, would be able to bind NAD(+) in the absence of an acetylated substrate. Indeed, we found that SIRT6 binds NAD(+) with relatively high affinity (K(d) = 27 ± 1 µM) in the absence of an acetylated substrate. Isothermal titration calorimetry and tryptophan fluorescence binding assays suggested that ADP-ribose and NAD(+) induce different structural perturbations and that NADH does not bind to SIRT6. Collectively, these new insights imply a unique activating mechanism and/or the possibility that SIRT6 could act as an NAD(+) metabolite sensor.

Cloning, expression and characterization of ferret CXCL10.

Chemokines and their receptors function in the recruitment and activation of cells of the immune system to sites of inflammation. As such, chemokines play an important role in mediating pathophysiological events during microbial infection. In particular, CXCL9, CXCL10 and CXCL11 and their cognate receptor CXCR3 have been associated with the clinical course of several infectious diseases, including severe acute respiratory syndrome (SARS) and influenza. While CXCL9, CXCL10 and CXCL11 share the same receptor and have overlapping functions, each can also have unique activity in host defense. The lack of a preferred characterized animal model for SARS has brought our attention to ferrets, which have been used for years in influenza studies. The lack of immunological reagents for ferrets prompted us to clone CXCL9, CXCL10, CXCL11 and CXCR3 and, in the case of CXCL10, to express the gene as a recombinant protein. In this study we demonstrate that endogenous ferret CXCL10 exhibits similar mRNA expression patterns in the lungs of deceased SARS patients and ferrets experimentally infected with SARS coronavirus. This study therefore represents an important step towards development of the ferret as a model for the role of CXCL9, CXCL10 and CXCL11:CXCR3 axis in severe viral infections.

Cloning, expression and immunoassay detection of ferret IFN-gamma.

Ferrets (Mustela putorius furo) develop symptoms upon influenza infection that resemble those of humans, including sneezing, body temperature variation and weight loss. Highly pathogenic strains of influenza A, such as H5N1, have the capacity to cause severe illness or death in ferrets. The use of ferrets as a model of influenza infection is currently limited by a lack of species-specific immunological reagents. Interferon gamma (IFN-gamma) plays a key role in the development of innate and adaptive immunity and the regulation of Th1-type immune responses. Here we describe the cloning of the full-length cDNA for ferret IFN-gamma. Multiple sequence alignment of the predicted amino acid sequence with those of other species indicates that the predicted ferret protein shares the highest identity with Eurasian badger IFN-gamma. We raised two hybridoma clones expressing monoclonal antibodies against recombinant ferret IFN-gamma capable of detecting IFN-gamma protein derived from mitogen-stimulated ferret PBMCs by immunoblotting, ELISA and ELISPOT assay. Finally, an ELISA utilizing the ferret-specific antibodies detected elevated levels of IFN-gamma in serum samples from H3N2 influenza A-infected ferrets.

Structure modeling of all identified G protein-coupled receptors in the human genome.

G protein-coupled receptors (GPCRs), encoded by about 5% of human genes, comprise the largest family of integral membrane proteins and act as cell surface receptors responsible for the transduction of endogenous signal into a cellular response. Although tertiary structural information is crucial for function annotation and drug design, there are few experimentally determined GPCR structures. To address this issue, we employ the recently developed threading assembly refinement (TASSER) method to generate structure predictions for all 907 putative GPCRs in the human genome. Unlike traditional homology modeling approaches, TASSER modeling does not require solved homologous template structures; moreover, it often refines the structures closer to native. These features are essential for the comprehensive modeling of all human GPCRs when close homologous templates are absent. Based on a benchmarked confidence score, approximately 820 predicted models should have the correct folds. The majority of GPCR models share the characteristic seven-transmembrane helix topology, but 45 ORFs are predicted to have different structures. This is due to GPCR fragments that are predominantly from extracellular or intracellular domains as well as database annotation errors. Our preliminary validation includes the automated modeling of bovine rhodopsin, the only solved GPCR in the Protein Data Bank. With homologous templates excluded, the final model built by TASSER has a global C(alpha) root-mean-squared deviation from native of 4.6 angstroms, with a root-mean-squared deviation in the transmembrane helix region of 2.1 angstroms. Models of several representative GPCRs are compared with mutagenesis and affinity labeling data, and consistent agreement is demonstrated. Structure clustering of the predicted models shows that GPCRs with similar structures tend to belong to a similar functional class even when their sequences are diverse. These results demonstrate the usefulness and robustness of the in silico models for GPCR functional analysis. All predicted GPCR models are freely available for noncommercial users on our Web site (http://www.bioinformatics.buffalo.edu/GPCR).

Regulation of B- and T-cell mediated xenogeneic transplant rejection by interleukin 12.

BACKGROUND: Xenotransplantation may provide a solution to the increasing shortage of donor organs. Acute vascular rejection and cell-mediated rejection remain the primary barriers to successful xenotransplantation. In animal models where acute vascular rejection can be attenuated, xenografts succumb to cell-mediated rejection. The mechanisms of acute vascular rejection and cell-mediated rejection are poorly understood. METHODS: Using a heterotopic rat-to-mouse cardiac transplantation model, we demonstrate that IL-12p40 attenuates both allogeneic and xenogeneic acute vascular rejection pathology by suppressing B-cell activation and anti-rat isotype switching. To study the mechanism of xenogeneic cell-mediated rejection, we use B-cell deficient mice that only develop cell-mediated rejection pathology. To elucidate the role of IL-12 in cell-mediated rejection, we generated B cell/ IL-12p40 double knockout mice. RESULTS: We demonstrate that xenogeneic cell-mediated rejection is mediated by CD4+ T cells, and is accompanied by elevated FasL and granzyme mRNA expression. Strikingly, by generating B cell/IL-12p40 double knockout mice, we demonstrate that xenogeneic cell-mediated rejection is IL-12p40 dependent. In contrast, we demonstrate that allogeneic cellular rejection is IL-12p40 independent. CONCLUSIONS: We conclude that IL-12 plays a dual role in xenotransplantation by driving xenogeneic CD4+ T cell responses but suppressing both allogeneic and xenogeneic B cell responses. Therefore, the mechanism of allogeneic and xenogeneic transplantation rejection is differentially regulated by IL-12.

Interferon-mediated immunopathological events are associated with atypical innate and adaptive immune responses in patients with severe acute respiratory syndrome.

It is not understood how immune inflammation influences the pathogenesis of severe acute respiratory syndrome (SARS). One area of strong controversy is the role of interferon (IFN) responses in the natural history of SARS. The fact that the majority of SARS patients recover after relatively moderate illness suggests that the prevailing notion of deficient type I IFN-mediated immunity, with hypercytokinemia driving a poor clinical course, is oversimplified. We used proteomic and genomic technology to systematically analyze host innate and adaptive immune responses of 40 clinically well-described patients with SARS during discrete phases of illness from the onset of symptoms to discharge or a fatal outcome. A novel signature of high IFN-alpha, IFN-gamma, and IFN-stimulated chemokine levels, plus robust antiviral IFN-stimulated gene (ISG) expression, accompanied early SARS sequelae. As acute illness progressed, SARS patients entered a crisis phase linked to oxygen saturation profiles. The majority of SARS patients resolved IFN responses at crisis and expressed adaptive immune genes. In contrast, patients with poor outcomes showed deviated ISG and immunoglobulin gene expression levels, persistent chemokine levels, and deficient anti-SARS spike antibody production. We contend that unregulated IFN responses during acute-phase SARS may culminate in a malfunction of the switch from innate immunity to adaptive immunity. The potential for the use of the gene signatures we describe in this study to better assess the immunopathology and clinical management of severe viral infections, such as SARS and avian influenza (H5N1), is therefore worth careful examination.

Defining the origins and evolution of the chemokine/chemokine receptor system.

The chemokine system has a critical role in mammalian immunity, but the evolutionary history of chemokines and chemokine receptors are ill-defined. We used comparative whole genome analysis of fruit fly, sea urchin, sea squirt, pufferfish, zebrafish, frog, and chicken to identify chemokines and chemokine receptors in each species. We report 127 chemokine and 70 chemokine receptor genes in the 7 species, with zebrafish having the most chemokines, 63, and chemokine receptors, 24. Fruit fly, sea urchin, and sea squirt have no identifiable chemokines or chemokine receptors. This study represents the most comprehensive analysis of the chemokine system to date and the only complete characterization of chemokine systems outside of mouse and human. We establish a clear evolutionary model of the chemokine system and trace the origin of the chemokine system to approximately 650 million years ago, identifying critical steps in their evolution and demonstrating a more extensive chemokine system in fish than previously thought.

CD80/CD86 costimulation regulates acute vascular rejection.

Xenotransplantation may provide the only solution to the shortage of human donor organs. Although hyperacute rejection associated with xenotransplantation can now be overcome, acute vascular rejection (AVR) remains a primary barrier to xenotransplantation. To date, standard immunosuppressive agents fail to block AVR or prolong xenograft survival. The present study was undertaken to determine the role of CD80/CD86 costimulatory molecules in regulating AVR. Lewis rat hearts were transplanted heterotopically into wild-type or IL-12, CD80- or CD86-deficient C57BL/6 mice. Wild-type recipients were treated with CD80 or CD86 neutralizing Ab with and without daily cyclosporin A (CsA, 15 mg/kg). Transplanted hearts in untreated wild-type recipients were rejected on postoperative days (POD) 17-21 and showed cell-mediated rejection (CMR) and AVR pathologies. In contrast, transplanted hearts in IL-12 and CD80 recipients or wild-type recipients treated with CD80 neutralizing Ab were rapidly rejected on POD 5 and 6 with AVR pathology. Interestingly, hearts transplanted into CD86 knockout recipients or wild-type recipients treated with CD86 neutralizing Ab underwent CMR on POD 17. Finally, blockade of CD86 but not CD80 rendered xenograft recipients sensitive to daily CsA therapy, leading to indefinite xenograft survival. To conclude, we demonstrate that AVR can be overcome by blocking the CD86 costimulatory pathway. Furthermore, we demonstrate that CD80 and CD86 have opposing roles in regulation of xenotransplantation rejection, where CD80 drives CMR and attenuates AVR while CD86 drives AVR. Most strikingly, indefinite xenograft survival can be achieved by suppressing AVR with CD86 neutralization in combination of CsA therapy, which inhibits CMR.

Genomic organization and evolution of the CX3CR1/CCR8 chemokine receptor locus.

The chemokine receptors CCR8 and CX3CR1 are key players in adaptive immunity and are co-receptors for human immunodeficiency virus. We describe here the genomic organization and evolutionary history of both of these genes. CX3CR1 has three promoters that transcribe three separate exons that are spliced with a fourth exon containing the coding region. CCR8 has two promoters. One promoter produces a transcript of two spliced exons, and the other promoter transcribes an exon containing the coding region and lacks introns. We analyzed these promoters in the context of a luciferase reporter and identified several positive and negative regulatory elements. Identification of the genomic organization of these genes in mouse demonstrates a similar organization for CCR8, but mouse CX3CR1 lacks two of the human promoters and has an additional mouse-specific promoter that transcribes only the exon containing the coding region and therefore resembles the organization of the human and mouse CCR8 genes. We also identify two nontranscribed regions that are highly conserved between human and mouse CX3CR1 containing possible regulatory elements. Examination of the CX3CR1 and CCR8 genes and surrounding genomic regions indicates that these genes are the result of the duplication of an ancestral gene prior to the divergence of teleost fish. We characterize single nucleotide polymorphisms in the promoters of human CCR8 and CX3CR1 and establish linkage relationships between CX3CR1 promoter polymorphisms and two previously described CX3CR1 coding polymorphisms associated with human immunodeficiency virus disease progression and arteriosclerosis susceptibility.

The role of chemokines and chemokine receptors in alloantigen-independent and alloantigen-dependent transplantation injury.

Transplantation injury and rejection involves the interplay of innate and acquired immune responses. Immune-related injury manifests itself in three temporal phases: early innate immune driven alloantigen-independent injury, acquired immune driven alloantigen-dependent injury, and chronic injury. Sequential waves of chemokine expression play a central role in regulating graft injury through the recruitment of phagocytes shortly after transplantation and activated lymphocytes and phagocytes in the weeks and years following transplantation. This review focuses on recent studies demonstrating the role of chemokines in transplantation.