The Cytokine IL-17A Limits Th17 Pathogenicity via a Negative Feedback Loop Driven by Autocrine Induction of IL-24.

Dysregulated Th17 cell responses underlie multiple inflammatory and autoimmune diseases, including autoimmune uveitis and its animal model, EAU. However, clinical trials targeting IL-17A in uveitis were not successful. Here, we report that Th17 cells were regulated by their own signature cytokine, IL-17A. Loss of IL-17A in autopathogenic Th17 cells did not reduce their pathogenicity and instead elevated their expression of the Th17 cytokines GM-CSF and IL-17F. Mechanistic in vitro studies revealed a Th17 cell-intrinsic autocrine loop triggered by binding of IL-17A to its receptor, leading to activation of the transcription factor NF-κB and induction of IL-24, which repressed the Th17 cytokine program. In vivo, IL-24 treatment ameliorated Th17-induced EAU, whereas silencing of IL-24 in Th17 cells enhanced disease. This regulatory pathway also operated in human Th17 cells. Thus, IL-17A limits pathogenicity of Th17 cells by inducing IL-24. These findings may explain the disappointing therapeutic effect of targeting IL-17A in uveitis.

CD8+ T cells reduce neuroretina inflammation in mouse by regulating autoreactive Th1 and Th17 cells through IFN-γ.

Various regulatory CD8+ T-cell subsets have been proposed for immune tolerance and have been implicated in controlling autoimmune diseases. However, their phenotypic identities and suppression mechanisms are not yet understood. This study found that coculture of T-cell receptor (TCR)- or interferon (IFN)-ß-activated CD8+ T cells significantly suppressed the cytokine production of Th1 and Th17 cells. By experimenting with the experimental autoimmune uveitis (EAU), we found that adoptive transfer of TCR or IFN-ß-activated CD8+ T cells significantly lessened disease development in an IFN-γ-dependent manner with a decreased uveitogenic Th1 and Th17 response. Interestingly, after adoptive transfer into the EAU mice, the IFN-γ+ CD8+ T cells were recruited more efficiently into the secondary lymphoid organs during the disease-priming phase. This recruitment depends on the IFN-γ-inducible chemokine receptor CXCR3; knocking out CXCR3 abolishes the protective effect of CD8+ T cells in EAU. In conclusion, we identified the critical role of IFN-γ for CD8+ T cells to inhibit Th1 and Th17 responses and ameliorate EAU. CXCR3 is necessary to recruit IFN-γ+ CD8+ T cells to the secondary lymphoid organ for the regulation of autoreactive Th1 and Th17 cells.

Editorial for the Special Issue "Cytokines in Inflammatory Signaling".

The intricate interplay of cytokines within the inflammatory response serves as a cornerstone of both the maintenance of physiological homeostasis and the pathogenesis of proinflammatory diseases [...].

Roles of Cytokines in Alzheimer's Disease.

The neuroimmune system is a collection of immune cells, cytokines, and the glymphatic system that plays a pivotal role in the pathogenesis and progression of Alzheimer's disease (AD). Of particular focus are cytokines, a group of immune signaling molecules that facilitate communication among immune cells and contribute to inflammation in AD. Extensive research has shown that the dysregulated secretion of certain cytokines (IL-1ß, IL-17, IL-12, IL-23, IL-6, and TNF-α) promotes neuroinflammation and exacerbates neuronal damage in AD. However, anti-inflammatory cytokines (IL-2, IL-3, IL-33, and IL-35) are also secreted during AD onset and progression, thereby preventing neuroinflammation. This review summarizes the involvement of pro- and anti-inflammatory cytokines in AD pathology and discusses their therapeutic potential.

AS101 ameliorates experimental autoimmune uveitis by regulating Th1 and Th17 responses and inducing Treg cells.

AS101 is an organotellurium compound with multifaceted immunoregulatory properties that is remarkable for its lack of toxicity. We tested the therapeutic effect of AS101 in experimental autoimmune uveitis (EAU), a model for human autoimmune uveitis. Unexpectedly, treatment with AS101 elicited Treg generation in vivo in otherwise unmanipulated mice. Mice immunized for EAU with the retinal antigen IRBP and treated with AS101 developed attenuated disease, as did AS101-treated recipients of retina-specific T cells activated in vitro. In both settings, eye-infiltrating effector T cells were decreased, whereas regulatory T (Treg) cells in the spleen were increased. Mechanistic studies in vitro revealed that AS101 restricted polarization of retina-specific T cells towards Th1 or Th17 lineage by repressing activation of their respective lineage-specific transcription factors and downstream signals. Retina-specific T cells polarized in vitro towards Th1 or Th17 in the presence of AS101 had impaired ability to induce EAU in naïve recipients. Finally, AS101 promoted differentiation of retina-specific T cells to Tregs in vitro independently of TGF-ß. We conclude that AS101 modulates autoimmune T cells by inhibiting acquisition and expression of effector function and by promoting Treg generation, and suggest that AS101 could be useful as a therapeutic approach for autoimmune uveitis.

IL-27p28 inhibits central nervous system autoimmunity by concurrently antagonizing Th1 and Th17 responses.

Central nervous system (CNS) autoimmunity such as uveitis and multiple sclerosis is accompanied by Th1 and Th17 responses. In their corresponding animal models, experimental autoimmune uveitis (EAU) and experimental autoimmune encephalomyelitis (EAE), both responses are induced and can drive disease independently. Because immune responses have inherent plasticity, therapeutic targeting of only one pathway could promote the other, without reducing pathology. IL-27p28 antagonizes gp130, required for signaling by IL-27 and IL-6, which respectively promote Th1 and Th17 responses. We therefore examined its ability to protect the CNS by concurrently targeting both effector responses. Overexpression of IL-27p28 in vivo ameliorated EAU as well as EAE pathology and reduced tissue infiltration by Th1 and Th17 cells in a disease prevention, as well as in a disease reversal protocol. Mechanistic studies revealed inhibition of Th1 and Th17 commitment in vitro and decreased lineage stability of pre-formed effectors in vivo, with reduction in expression of gp130-dependent transcription factors and cytokines. Importantly, IL-27p28 inhibited polarization of human T cells to the Th1 and Th17 effector pathways. The ability of IL-27p28 to inhibit generation as well as function of pathogenic Th1 and Th17 effector cells has therapeutic implications for controlling immunologically complex autoimmune diseases.

The living eye "disarms" uncommitted autoreactive T cells by converting them to Foxp3(+) regulatory cells following local antigen recognition.

Immune privilege is used by the eye, brain, reproductive organs, and gut to preserve structural and functional integrity in the face of inflammation. The eye is arguably the most vulnerable and, therefore, also the most "privileged" of tissues; paradoxically, it remains subject to destructive autoimmunity. It has been proposed, although never proven in vivo, that the eye can induce T regulatory cells (Tregs) locally. Using Foxp3-GFP reporter mice expressing a retina-specific TCR, we now show that uncommitted T cells rapidly convert in the living eye to Foxp3(+) Tregs in a process involving retinal Ag recognition, de novo Foxp3 induction, and proliferation. This takes place within the ocular tissue and is supported by retinoic acid, which is normally present in the eye because of its function in the chemistry of vision. Nonconverted T cells showed evidence of priming but appeared restricted from expressing effector function in the eye. Pre-existing ocular inflammation impeded conversion of uncommitted T cells into Tregs. Importantly, retina-specific T cells primed in vivo before introduction into the eye were resistant to Treg conversion in the ocular environment and, instead, caused severe uveitis. Thus, uncommitted T cells can be disarmed, but immune privilege is unable to protect from uveitogenic T cells that have acquired effector function prior to entering the eye. These findings shed new light on the phenomenon of immune privilege and on its role, as well as its limitations, in actively controlling immune responses in the tissue.

Regulation of Treg cells by cytokine signaling and co-stimulatory molecules.

CD4+CD25+Foxp3+ regulatory T cells (Tregs), a vital component of the immune system, are responsible for maintaining immune homeostasis and preventing excessive immune responses. This review explores the signaling pathways of the cytokines that regulate Treg cells, including transforming growth factor beta (TGF-ß), interleukin (IL)-2, IL-10, and IL-35, which foster the differentiation and enhance the immunosuppressive capabilities of Tregs. It also examines how, conversely, signals mediated by IL-6 and tumor necrosis factor -alpha (TNF-α) can undermine Treg suppressive functions or even drive their reprogramming into effector T cells. The B7 family comprises indispensable co-stimulators for T cell activation. Among its members, this review focuses on the capacity of CTLA-4 and PD-1 to regulate the differentiation, function, and survival of Tregs. As Tregs play an essential role in maintaining immune homeostasis, their dysfunction contributes to the pathogenesis of autoimmune diseases. This review delves into the potential of employing Treg-based immunotherapy for the treatment of autoimmune diseases, transplant rejection, and cancer. By shedding light on these topics, this article aims to enhance our understanding of the regulation of Tregs by cytokines and their therapeutic potential for various pathological conditions.

Breakdown of immune privilege and spontaneous autoimmunity in mice expressing a transgenic T cell receptor specific for a retinal autoantigen.

Despite presence of circulating retina-specific T cells in healthy individuals, ocular immune privilege usually averts development of autoimmune uveitis. To study the breakdown of immune privilege and development of disease, we generated transgenic (Tg) mice that express a T cell receptor (TCR) specific for interphotoreceptor retinoid-binding protein (IRBP), which serves as an autoimmune target in uveitis induced by immunization. Three lines of TCR Tg mice, with different levels of expression of the transgenic R161 TCR and different proportions of IRBP-specific CD4⁺ T cells in their peripheral repertoire, were successfully established. Importantly, two of the lines rapidly developed spontaneous uveitis, reaching 100% incidence by 2 and 3 months of age, respectively, whereas the third appeared "poised" and only developed appreciable disease upon immune perturbation. Susceptibility roughly paralleled expression of the R161 TCR. In all three lines, peripheral CD4⁺ T cells displayed a naïve phenotype, but proliferated in vitro in response to IRBP and elicited uveitis upon adoptive transfer. In contrast, CD4⁺ T cells infiltrating uveitic eyes mostly showed an effector/memory phenotype, and included Th1, Th17 as well as T regulatory cells that appeared to have been peripherally converted from conventional CD4⁺ T cells rather than thymically derived. Thus, R161 mice provide a new and valuable model of spontaneous autoimmune disease that circumvents the limitations of active immunization and adjuvants, and allows to study basic mechanisms involved in maintenance and breakdown of immune homeostasis affecting immunologically privileged sites such as the eye.

Mannose-binding lectin contributes to deleterious inflammatory response in pandemic H1N1 and avian H9N2 infection.

BACKGROUND: Mannose-binding lectin (MBL) is a pattern-recognition molecule, which functions as a first line of host defense. Pandemic H1N1 (pdmH1N1) influenza A virus caused massive infection in 2009 and currently circulates worldwide. Avian influenza A H9N2 (H9N2/G1) virus has infected humans and has the potential to be the next pandemic virus. Antiviral function and immunomodulatory role of MBL in pdmH1N1 and H9N2/G1 virus infection have not been investigated. METHODS: In this study, MBL wild-type (WT) and MBL knockout (KO) murine models were used to examine the role of MBL in pdmH1N1 and H9N2/G1 virus infection. RESULTS: Our study demonstrated that in vitro, MBL binds to pdmH1N1 and H9N2/G1 viruses, likely via the carbohydrate recognition domain of MBL. Wild-type mice developed more severe disease, as evidenced by a greater weight loss than MBL KO mice during influenza virus infection. Furthermore, MBL WT mice had enhanced production of proinflammatory cytokines and chemokines compared with MBL KO mice, suggesting that MBL could upregulate inflammatory responses that may potentially worsen pdmH1N1 and H9N2/G1 virus infections. CONCLUSIONS: Our study provided the first in vivo evidence that MBL may be a risk factor during pdmH1N1 and H9N2/G1 infection by upregulating proinflammatory response.

Regulatory T cell intravitreal delivery using hyaluronan methylcellulose hydrogel improves therapeutic efficacy in experimental autoimmune uveitis.

Autoimmune uveitis refers to several intraocular inflammation conditions, which are mediated by autoreactive T cells. Regulatory T cells (Tregs) are immunosuppressive cells that have shown potential for resolving various autoimmune diseases, including uveitis. However, poor donor cell dispersion distal to the injection site and plasticity of Treg cells in an inflammatory microenvironment can present obstacles for this immunotherapy. We assessed the use of a physical blend of hyaluronan and methylcellulose (HAMC) as immunoprotective and injectable hydrogel cell delivery system to improve the efficacy of Treg-based therapy in treating experimental autoimmune uveitis (EAU). We demonstrated that the Treg-HAMC blend increased both the survival and stability of Tregs under proinflammatory conditions. Furthermore, we found that the intravitreal HAMC delivery system resulted in a two-fold increase in the number of transferred Tregs in the inflamed eye of EAU mice. Treg-HAMC delivery effectively attenuated ocular inflammation and preserved the visual function of EAU mice. It significantly decreased the number of ocular infiltrates, including the uveitogenic IFN-γ+CD4+ and IL-17+CD4+ T cells. In contrast, intravitreal injection of Treg cells without HAMC only achieved marginal therapeutic effects in EAU. Our findings suggest that HAMC may become a promising delivery vehicle for human uveitis Treg therapy.

Natural killer cells become tolerogenic after interaction with apoptotic cells.

NK cells are effectors in innate immunity and also participate in immunoregulation through the release of TGF-beta1 and lysis of activated/autoreactive T cells. Apoptotic cells (AC) have been shown to induce tolerogenic properties in innate immune cells, including macrophages and dendritic cells, but not NK cells. In this study, we demonstrated that after interaction with AC, NK cells released TGF-beta1, which in turn suppressed the production of IFN-gamma by NK cells upon IL-12 and IgG activation. We further identified phosphatidylserine as a potential target on AC for the NK cells, as phosphatidylserine could stimulate NK cells to release TGF-beta1, which in turn suppressed CD4(+) T-cell proliferation and activation. Moreover, AC-treated NK cells displayed cytotoxicity against autologous-activated CD4(+) T cells by upregulating NKp46. This lysis occurred in part through the NKp46-vimentin pathway, as activated CD4(+) T cells expressed vimentin on the cell surface and blocking of vimentin or NKp46, but not other NK-cell receptors, significantly suppressed the NK-cell cytotoxicity. We report here a novel interaction between NK cells and AC, resulting in the tolerogenic properties of NK cells required for immune contraction.

Induction of antigen-specific Treg cells in treating autoimmune uveitis via bystander suppressive pathways without compromising anti-tumor immunity.

BACKGROUND: Induction of autoantigen-specific Treg cells that suppress tissue-specific autoimmunity without compromising beneficial immune responses is the holy-grail for immunotherapy to autoimmune diseases. METHODS: In a model of experimental autoimmune uveitis (EAU) that mimics human uveitis, ocular inflammation was induced by immunization with retinal antigen interphotoreceptor retinoid-binding protein (IRBP). Mice were given intraperitoneal injection of αCD4 antibody (Ab) after the onset of disease, followed by administration of IRBP. EAU was evaluated clinically and functionally. Splenocytes, CD4+CD25- and CD4+CD25+ T cells were sorted and cultured with IRBP or αCD3 Ab. T cell proliferation and cytokine production were assessed. FINDINGS: The experimental approach resulted in remission of ocular inflammation and rescue of visual function in mice with established EAU. Mechanistically, the therapeutic effect was mediated by induction of antigen-specific Treg cells that inhibited IRBP-driven Th17 response in TGF-ß and IL-10 dependent fashion. Importantly, the Ab-mediated immune tolerance could be achieved in EAU mice by administration of retinal autoantigens, arrestin but not limited to IRBP only, in an antigen-nonspecific bystander manner. Further, these EAU-suppressed tolerized mice did not compromise their anti-tumor T immunity in melanoma model. INTERPRETATION: We successfully addressed a specific immunotherapy of EAU by in vivo induction of autoantigen-specific Treg cells without compromising host overall T cell immunity, which should have potential implication for patients with autoimmune uveitis. FUNDING: This study was supported by the Natural Science Foundation of Guangdong Province and the Fundamental Research Fund of the State Key Laboratory of Ophthalmology, Zhongshan Ophthalmic Center.

Type I Interferon Therapy Limits CNS Autoimmunity by Inhibiting CXCR3-Mediated Trafficking of Pathogenic Effector T Cells.

Type I interferons (IFNs) have therapeutic potential in CNS autoimmune diseases, such as uveitis, but the molecular mechanisms remain unclear. Using a T cell-transfer model of experimental autoimmune uveitis (EAU), we found that IFN-α/ß treatment inhibited the migration of IFN-γ-producing pathogenic CD4+ T cells to effector sites. IFN-α/ß upregulated the expression of the cognate ligands CXCL9, CXCL10, and CXCL11, causing ligand-mediated downregulation of CXCR3 expression and effector T cell retention in the spleen. Accordingly, type I IFN did not alter EAU progression in CXCR3-/- mice. In uveitis patients, disease exacerbations correlated with reduced serum IFN-α concentrations. IFN-α/ß reduced CXCR3 expression and migration by human effector T cells, and these parameters were associated with the therapeutic efficacy of IFN-α in uveitis patients. Our findings provide insight into the molecular basis of type I IFN therapy for CNS autoimmune diseases and identify CXCR3 as a biomarker for effective type I IFN immunotherapy.

IL-20 receptor cytokines in autoimmune diseases.

IL-19, IL-20, and IL-24 are the members of IL-10 family. They are also known as IL-20 receptor (IL-20R) cytokines as they all signal through the IL-20RA/IL-20RB receptor complex; IL-20 and IL-24 (but not IL-19) also signal through the IL-20RB/IL22RA1 receptor complex. Despite their protein structure homology and shared use of receptor complexes, they display distinct biological functions in immune regulation, tissue homeostasis, host defense, and oncogenesis. IL-20R cytokines can be expressed by both immune cells and epithelial cells, and are important for their interaction. In general, these cytokines are considered to be associated with pathogenesis of chronic inflammation and autoimmune diseases, including psoriasis, rheumatoid arthritis, and inflammatory bowel disease. However, a number of studies also highlighted their suppressive functions in regulating both innate and adaptive T cell responses and other immune cells, suggesting that the role of IL-20R cytokines in autoimmunity may be complex. In this review, we will discuss the immunobiological functions of IL-20R cytokines and how they are involved in regulating autoimmune diseases.

Comparative Analysis of the Interphotoreceptor Retinoid Binding ProteinInduced Models of Experimental Autoimmune Uveitis in B10.RIII versus C57BL/6 Mice.

OBJECTIVE: Experimental autoimmune uveitis (EAU) represents autoimmune uveitis in humans, among which B10.RIII and C57BL/6 are the frequently used strains in mice, but to date, no study has been reported to compare EAU disease between the two strains. Here we compared the differences in morphology, pathology, visual function of the retinal inflammation and Th1/Th17 immune responses in the EAU models induced by the interphotoreceptor retinoid binding protein (IRBP) between the B10.RIII and C57BL/6 strains, using fundus and histological examinations, optical coherence tomography, electroretinography and immunoassays. METHOD: EAU induced in B10.RIII mice exhibited a shortterm severe inflammation with massive ocular infiltrates of inflammatory cells and extensive destruction of the retina that culminated in rapid degeneration of the retina and permanent loss of visual function. In contrast, C57BL/6 mice developed chronic inflammation with recurring and persistent retinitis for several months, highlighting moderate scores of disease severity and visual signal in comparison with those in B10.RIII mice. Consistent with the clinical manifestations, increased Th1/Th17 effector responses were detected in the uveitic eyes of B10.RIII strain than those in C57BL/6 strain. These data demonstrate distinguishing features of retinal inflammation and T-cell immune responses involved in IRBP-induced EAU between B10.RIII and C57BL/6 strains. CONCLUSION: Our findings suggest that the persistent-recurring EAU model induced in C57BL/6 mice may serve as a better tool to represent distinct aspects of human uveitis.

The association of RANTES polymorphism with severe acute respiratory syndrome in Hong Kong and Beijing Chinese.

BACKGROUND: Chemokines play important roles in inflammation and antiviral action. We examined whether polymorphisms of RANTES, IP-10 and Mig affect the susceptibility to and outcome of severe acute respiratory syndrome (SARS). METHODS: We tested the polymorphisms of RANTES, IP-10 and Mig for their associations with SARS in 495 Hong Kong Chinese SARS patients and 578 controls. Then we tried to confirm the results in 356 Beijing Chinese SARS patients and 367 controls. RESULTS: RANTES -28 G allele was associated with SARS susceptibility in Hong Kong Chinese (P < 0.0001, OR = 2.80, 95%CI:2.11-3.71). Individuals with RANTES -28 CG and GG genotypes had a 3.28-fold (95%CI:2.32-4.64) and 3.06-fold (95%CI:1.47-6.39) increased risk of developing SARS respectively (P < 0.0001). This -28 G allele conferred risk of death in a gene-dosage dependent manner (P = 0.014) with CG and GG individuals having a 2.12-fold (95% CI: 1.11-4.06) and 4.01-fold (95% CI: 1.30-12.4) increased risk. For the replication of RANTES data in Beijing Chinese, the -28 G allele was not associated with susceptibility to SARS. However, -28 CG (OR = 4.27, 95%CI:1.64-11.1) and GG (OR = 3.34, 95%CI:0.37-30.7) were associated with admission to intensive care units or death due to SARS (P = 0.011). CONCLUSION: RANTES -28 G allele plays a role in the pathogenesis of SARS.

The interferon gamma gene polymorphism +874 A/T is associated with severe acute respiratory syndrome.

BACKGROUND: Cytokines play important roles in antiviral action. We examined whether polymorphisms of IFN-gamma,TNF-alpha and IL-10 affect the susceptibility to and outcome of severe acute respiratory syndrome (SARS). METHODS: A case-control study was carried out in 476 Chinese SARS patients and 449 healthy controls. We tested the polymorphisms of IFN-gamma,TNF-alpha and IL-10 for their associations with SARS. RESULTS: IFN-gamma +874A allele was associated with susceptibility to SARS in a dose-dependent manner (P < 0.001). Individuals with IFN-gamma +874 AA and AT genotype had a 5.19-fold (95% Confidence Interval [CI], 2.78-9.68) and 2.57-fold (95% CI, 1.35-4.88) increased risk of developing SARS respectively. The polymorphisms of IL-10 and TNF-alpha were not associated with SARS susceptibility. CONCLUSION: IFN-gamma +874A allele was shown to be a risk factor in SARS susceptibility.

NK-DC crosstalk controls the autopathogenic Th17 response through an innate IFN-γ-IL-27 axis.

IFN-γ is a pathogenic cytokine involved in inflammation. Paradoxically, its deficiency exacerbates experimental autoimmune encephalomyelitis, uveitis, and arthritis. Here, we demonstrate using IFN-γ(-/-) mice repleted with IFN-γ +/+: NK cells that innate production of IFN-γ from NK cells is necessary and sufficient to trigger an endogenous regulatory circuit that limits autoimmunity. After immunization, DCs recruited IFN-γ-producing NK cells to the draining lymph node and interacted with them in a CXCR3-dependent fashion. The interaction caused DCs to produce IL-27, which in turn enhanced IFN-γ production by NK cells, forming a self-amplifying positive feedback loop. IL-10, produced by the interacting cells themselves, was able to limit this process. The NK-DC-dependent IL-27 inhibited development of the adaptive pathogenic IL-17 response and induced IL-10-producing Tr1-like cells, which ameliorated disease in an IL-10-dependent manner. Our data reveal that an early NK-DC interaction controls the adaptive Th17 response and limits tissue-specific autoimmunity through an innate IFN-γ-IL-27 axis.

Functional polymorphisms of the CCL2 and MBL genes cumulatively increase susceptibility to severe acute respiratory syndrome coronavirus infection.

OBJECTIVES: To assess associations between the functional polymorphisms G-2518A at the chemokine (C-C motif) ligand 2 gene (CCL2) and mannose binding lectin (MBL) codon 54 variant (A/B) and susceptibility to SARS. METHODS: We genotyped the CCL2 G-2518A and MBL codon 54 variant (A/B) in 4 case-control populations of Chinese descent, totally consisting of 932 patients with SARS and 982 control subjects. RESULTS: Both the high-CCL2-producing GG genotype and the low-MBL-producing B allele were consistently associated with increased risks of SARS-CoV infection in all 4 case-control populations (joint P = 1.6 × 10(-4) and 4.9 × 10(-8), for CCL2 and MBL respectively), with no interaction between polymorphisms could be detected. Furthermore, all the 4 case-control studies demonstrated a cumulative effect on risk of SARS-CoV infection for the combination of polymorphisms (joint P = 1.3 × 10(-10)). However, tests using the area under the curve (AUC) indicated that at this stage, the polymorphisms were unlikely to be appropriate for risk prediction testing because of low AUC values (all <66%). Additionally, no association was observed between the polymorphisms and severity of SARS. CONCLUSIONS: The CCL2 G-2518A and MBL codon 54 variant have a significantly cumulative effect on increased risk of SARS-CoV infection.