The heat-stable antigen determines pathogenicity of self-reactive T cells in experimental autoimmune encephalomyelitis

Surprising magic of CD24 beyond cancer

CD24 has emerged as a molecule of significant interest beyond the oncological arena. Recent studies have unveiled its surprising and diverse roles in various biological processes and diseases. This review encapsulates the expanding spectrum of CD24 functions, delving into its involvement in immune regulation, cancer immune microenvironment, and its potential as a therapeutic target in autoimmune diseases and beyond. The 'magic' of CD24, once solely attributed to cancer, now inspires a new paradigm in understanding its multifunctionality in human health and disease, offering exciting prospects for medical advancements.

CD24-Siglec interactions in inflammatory diseases

CD24 is a small glycosylphosphatidylinositol (GPI)-anchored glycoprotein with broad expression in multiple cell types. Due to differential glycosylation, cell surface CD24 have been shown to interact with various receptors to mediate multiple physiological functions. Nearly 15 years ago, CD24 was shown to interact with Siglec G/10 to selectively inhibit inflammatory response to tissue injuries. Subsequent studies demonstrate that sialylated CD24 (SialoCD24) is a major endogenous ligand for CD33-family of Siglecs to protect the host against inflammatory and autoimmune diseases, metabolic disorders and most notably respiratory distress in COVID-19. The discoveries on CD24-Siglec interactions propelled active translational research to treat graft-vs-host diseases, cancer, COVID-19 and metabolic disorders. This mini-review provides a succinct summary on biological significance of CD24-Siglec pathway in regulation of inflammatory diseases with emphasis on clinical translation.

Dendritic cell expression of CD24 contributes to optimal priming of T lymphocytes in lymph nodes

CD24 is a GPI anchored cell surface glycoprotein whose function as a co-stimulatory molecule has been implicated. However, the function of CD24 on antigen presenting cells during T cell responses is not well understood. Here we show that in the CD24-deficient host, adoptively transferred CD4+ T cells undergo inefficient expansion and have accelerated cell death in lymph nodes, which results in insufficient priming of T cells. Insufficient expansion of T cells in the CD24-deficient host was not due to host anti-CD24 response by NK, T and B lymphocytes. Transgenic expression of CD24 on DC in CD24-/- mice restored T cell accumulation and survival in draining lymph nodes. Consistent with these findings, MHC II tetramer staining also revealed that an antigen-specific polyclonal T cell response was reduced in lymph nodes of CD24-/- mice. Taken together, we have revealed a novel role of CD24 on DC in optimal T cell priming in lymph nodes. These data suggest that CD24 blockade should lower unwanted T cell responses such as those in autoimmune diseases.

Emerging phagocytosis checkpoints in cancer immunotherapy

Cancer immunotherapy, mainly including immune checkpoints-targeted therapy and the adoptive transfer of engineered immune cells, has revolutionized the oncology landscape as it utilizes patients' own immune systems in combating the cancer cells. Cancer cells escape immune surveillance by hijacking the corresponding inhibitory pathways via overexpressing checkpoint genes. Phagocytosis checkpoints, such as CD47, CD24, MHC-I, PD-L1, STC-1 and GD2, have emerged as essential checkpoints for cancer immunotherapy by functioning as "don't eat me" signals or interacting with "eat me" signals to suppress immune responses. Phagocytosis checkpoints link innate immunity and adaptive immunity in cancer immunotherapy. Genetic ablation of these phagocytosis checkpoints, as well as blockade of their signaling pathways, robustly augments phagocytosis and reduces tumor size. Among all phagocytosis checkpoints, CD47 is the most thoroughly studied and has emerged as a rising star among targets for cancer treatment. CD47-targeting antibodies and inhibitors have been investigated in various preclinical and clinical trials. However, anemia and thrombocytopenia appear to be formidable challenges since CD47 is ubiquitously expressed on erythrocytes. Here, we review the reported phagocytosis checkpoints by discussing their mechanisms and functions in cancer immunotherapy, highlight clinical progress in targeting these checkpoints and discuss challenges and potential solutions to smooth the way for combination immunotherapeutic strategies that involve both innate and adaptive immune responses.

Soluble CD24 is an inflammatory biomarker in early and seronegative rheumatoid arthritis

Introduction: Rheumatoid arthritis (RA) is a chronic, systemic autoimmune disease characterized by autoantibody production, joint inflammation and bone destruction. Nearly 1/3 of RA patients with the active disease also exhibit a normal range of ESR and CRP. Here we assessed the performance and clinical significance of soluble CD24 (sCD24) as a biomarker of disease activity in RA.Methods: A total of 269 RA patients, 59 primary Sjogren's syndrome (SS) patients, 81 systematic lupus erythematosus (SLE) patients, 76 osteoarthritis (OA) patients and 97 healthy individuals (HC) were included in this study. Soluble CD24 in sera were detected by ELISA. Therefore, the concentration of sCD24 was analyzed in RA patients with different disease activity statuses.Results: The sCD24 was significantly increased in RA (2970 pg/mL), compared to other rheumatic diseases (380-520 pg/mL) and healthy individuals (320 pg/mL). Moreover, sCD24 was elevated in 66.67% of early RA and 61.11% of seronegative RA patients. In addition, sCD24 was significantly correlated with the disease duration and inflammatory indicators.Conclusion: The sCD24 could be an inflammatory biomarker in RA patients, especially in early and seronegative patients.

Insights into CD24 and Exosome Physiology and Potential Role in View of Recent Advances in COVID-19 Therapeutics: A Narrative Review

Cluster of differentiation (CD) 24, a long-known protein with multifaceted functions, has gained attention as a possible treatment for Coronavirus Disease 19 (COVID-19) due to its known anti-inflammatory action. Extracellular vesicles (EVs), such as exosomes and microvesicles, may serve as candidate drug delivery platforms for novel therapeutic approaches in COVID-19 and various other diseases due to their unique characteristics. In the current review, we describe the physiology of CD24 and EVs and try to elucidate their role, both independently and as a combination, in COVID-19 therapeutics. CD24 may act as an important immune regulator in diseases with complex physiologies characterized by excessive inflammation. Very recent data outline a possible therapeutic role not only in COVID-19 but also in other similar disease states, e.g., acute respiratory distress syndrome (ARDS) and sepsis where immune dysregulation plays a key pathophysiologic role. On the other hand, CD24, as well as other therapeutic molecules, can be administered with the use of exosomes, exploiting their unique characteristics to create a novel drug delivery platform as outlined in recent clinical efforts. The implications for human therapeutics in general are huge with regard to pharmacodynamics, pharmacokinetics, safety, and efficacy that will be further elucidated in future randomized controlled trials (RCTs).

CD24-Siglec axis is an innate immune checkpoint against metaflammation and metabolic disorder

The molecular interactions that regulate chronic inflammation underlying metabolic disease remain largely unknown. Since the CD24-Siglec interaction regulates inflammatory response to danger-associated molecular patterns (DAMPs), we have generated multiple mouse strains with single or combined mutations of Cd24 or Siglec genes to explore the role of the CD24-Siglec interaction in metaflammation and metabolic disorder. Here, we report that the CD24-Siglec-E axis, but not other Siglecs, is a key suppressor of obesity-related metabolic dysfunction. Inactivation of the CD24-Siglec-E pathway exacerbates, while CD24Fc treatment alleviates, diet-induced metabolic disorders, including obesity, dyslipidemia, insulin resistance, and nonalcoholic steatohepatitis (NASH). Mechanistically, sialylation-dependent recognition of CD24 by Siglec-E induces SHP-1 recruitment and represses metaflammation to protect against metabolic syndrome. A first-in-human study of CD24Fc (NCT02650895) supports the significance of this pathway in human lipid metabolism and inflammation. These findings identify the CD24-Siglec-E axis as an innate immune checkpoint against metaflammation and metabolic disorder and suggest a promising therapeutic target for metabolic disease.

CD24 is expressed on FoxP3+ regulatory T cells and regulates their function

CD24 is a glycosyl-phosphatidylinositol (GPI) anchored cell surface glycoprotein with a variety of immunomodulatory functions such as inhibition of thymic generation of autoreactive T cells, regulation of antigen presenting cell functions, and mediation of autoimmunity. Given the autoimmune nature of FoxP3+ regulatory T cells and their importance in autoimmune diseases, we hypothesize that CD24 regulates the generation and functions of Treg cells. Through the analysis of the Treg repertoire in two strains of CD24-deficient mice, we found that CD24 does not globally affect the thymic generation of Treg cells. However, CD24 is abundantly expressed on Treg cells, and CD24 antibody treatment of Treg cells enhances their suppressive functions. Concurrently, we observed CD24-deficient Treg cells exhibit increased suppressive functions and produce more IL-10 compared to their wild type counterparts. In addition, CD24-deficient Treg cells exhibited more potent suppressive capacity in inhibiting the development of experimental autoimmune encephalomyelitis (EAE) in mice. Thus, CD24 on Treg cells regulates their suppressive functions. Our findings can partially explain the resistance of EAE development in CD24-deficient mice and CD24 polymorphism-associated susceptibility of human autoimmune diseases. Further investigations regarding mechanisms of CD24 regulation of Treg function may lead to a new approach for the immunotherapy of human autoimmune diseases.

Targeting macrophage-mediated tumor cell phagocytosis: An overview of phagocytosis checkpoints blockade, nanomedicine intervention, and engineered CAR-macrophage therapy

Immunotherapy has been developing at an unprecedented speed with promising therapeutic outcomes in the wide spectrum of cancers. Up until now, most immunotherapies have focused on adaptive immunity; however, investigating the potential of macrophage phagocytosis and consequent adaptive immune cross-priming has led to a growing interest in exploiting macrophages in cancer therapy. In light of the positive evidence from preclinical studies and early clinical data, targeting macrophage phagocytosis has become a promising therapeutic strategy. Here, we review therapies based on harnessing and amplifying macrophage phagocytosis, such as blocking phagocytosis checkpoints and exploiting nanoparticles as efficient approaches in elevating macrophages-mediated phagocytosis. The present study introduces CAR-macrophage as the state-of-the-art modality serving as the bridge between the innate and adaptive immune system to mount a superior anti-tumor response in the treatment of cancer. We also take a look at the recent reports of therapies based on CAR-engineered macrophages with the hope of providing a future research direction for expanding the application of CAR-macrophage therapy.

Lack of NFATc1 SUMOylation prevents autoimmunity and alloreactivity

Posttranslational modification with SUMO is known to regulate the activity of transcription factors, but how SUMOylation of individual proteins might influence immunity is largely unexplored. The NFAT transcription factors play an essential role in antigen receptor-mediated gene regulation. SUMOylation of NFATc1 represses IL-2 in vitro, but its role in T cell-mediated immune responses in vivo is unclear. To this end, we generated a novel transgenic mouse in which SUMO modification of NFATc1 is prevented. Avoidance of NFATc1 SUMOylation ameliorated experimental autoimmune encephalomyelitis as well as graft-versus-host disease. Elevated IL-2 production in T cells promoted T reg expansion and suppressed autoreactive or alloreactive immune responses. Mechanistically, increased IL-2 secretion counteracted IL-17 and IFN-γ expression through STAT5 and Blimp-1 induction. Then, Blimp-1 repressed IL-2 itself, as well as the induced, proliferation-associated survival factor Bcl2A1. Collectively, these data demonstrate that prevention of NFATc1 SUMOylation fine-tunes T cell responses toward lasting tolerance. Thus, targeting NFATc1 SUMOylation presents a novel and promising strategy to treat T cell-mediated inflammatory diseases.

Exosome-Based Vaccines: History, Current State, and Clinical Trials

Extracellular vesicles (EVs) are released by most cell types as part of an intracellular communication system in crucial processes such as inflammation, cell proliferation, and immune response. However, EVs have also been implicated in the pathogenesis of several diseases, such as cancer and numerous infectious diseases. An important feature of EVs is their ability to deliver a wide range of molecules to nearby targets or over long distances, which allows the mediation of different biological functions. This delivery mechanism can be utilized for the development of therapeutic strategies, such as vaccination. Here, we have highlighted several studies from a historical perspective, with respect to current investigations on EV-based vaccines. For example, vaccines based on exosomes derived from dendritic cells proved to be simpler in terms of management and cost-effectiveness than dendritic cell vaccines. Recent evidence suggests that EVs derived from cancer cells can be leveraged for therapeutics to induce strong anti-tumor immune responses. Moreover, EV-based vaccines have shown exciting and promising results against different types of infectious diseases. We have also summarized the results obtained from completed clinical trials conducted on the usage of exosome-based vaccines in the treatment of cancer, and more recently, coronavirus disease.

Behavioral Characterizing of CD24 Knockout Mouse-Cognitive and Emotional Alternations

CD24 is a small, glycophosphatidylinositol-anchored cell surface protein, mostly investigated with respect to cancer, inflammation, and autoimmune diseases. CD24 knockdown or inhibition has been used to test various biochemical mechanisms and neurological conditions; however, the association between CD24 and behavioral phenotypes has not yet been examined. This study aims to characterize cognitive and emotional functions of CD24 knockout mice (CD24-/-) compared with CD24 wild-type mice at three time-points: adolescence, young adulthood, and adulthood. Our results show that CD24-/- mice exhibited better cognitive performance and less anxiety-like behavior compared with WT mice, with no effect on depression-like behavior. This phenotype was constant from childhood (2 months old) to adulthood (6 months old). The results from our study suggest that CD24 may influence important behavioral aspects at the whole-organism level, which should be taken into consideration when using CD24 knockout models.

Novel insights into the function of CD24: A driving force in cancer

CD24 is a highly glycosylated protein with a small protein core that is linked to the plasma membrane via a glycosyl-phosphatidylinositol anchor. CD24 is primarily expressed by immune cells but is often overexpressed in human tumors. In cancer, CD24 is a regulator of cell migration, invasion and proliferation. Its expression is associated with poor prognosis and it is used as cancer stemness marker. Recently, CD24 on tumor cells was identified as a phagocytic inhibitor ("do not eat me" signal) having a suppressive role in tumor immunity via binding to Siglec-10 on macrophages. This finding is reminiscent of the demonstration that soluble CD24-Fc can dampen the immune system in autoimmune disease. In the present review, we summarize recent progress on the role of the CD24-Siglec-10 binding axis at the interface between tumor cells and the immune system, and the role of CD24 genetic polymorphisms in cancer. We describe the specific function of cytoplasmic CD24 and discuss the presence of CD24 on tumor-released extracellular vesicles. Finally, we evaluate the potential of CD24-based immunotherapy.

Association between CD24 Ala/Val polymorphism and multiple sclerosis risk: A meta analysis

BACKGROUND

The aim of this study was to explore the association between CD24 Ala/Val polymorphism and susceptibility of multiple sclerosis (MS).

METHODS

A comprehensive literature search for relevant studies was performed on google scholar, PubMed, Web of science, Embase, the Chinese National Knowledge Infrastructure and the Chinese Biology Medicine. This meta-analysis was conducted using the STATA 11.0 software and the pooled odds ratio with 95% confidence interval was calculated.

RESULTS

Seven case-control studies were included in this meta-analysis. The results showed significant association between CD24 Ala/Val polymorphism and susceptibility to MS. Stratified analysis by areas also showed significant association in Asians. However, no association was found in Europeans.

CONCLUSION

This study suggested that the CD24 Val allele was associated with an increased risk of MS and larger-scale studies of populations are needed to explore the role of CD24 Ala/Val polymorphism during the pathogenesis of MS.

Febrile Temperature Critically Controls the Differentiation and Pathogenicity of T Helper 17 Cells

Fever, an evolutionarily conserved physiological response to infection, is also commonly associated with many autoimmune diseases, but its role in T cell differentiation and autoimmunity remains largely unclear. T helper 17 (Th17) cells are critical in host defense and autoinflammatory diseases, with distinct phenotypes and pathogenicity. Here, we show that febrile temperature selectively regulated Th17 cell differentiation in vitro in enhancing interleukin-17 (IL-17), IL-17F, and IL-22 expression. Th17 cells generated under febrile temperature (38.5°C-39.5°C), compared with those under 37°C, showed enhanced pathogenic gene expression with increased pro-inflammatory activities in vivo. Mechanistically, febrile temperature promoted SUMOylation of SMAD4 transcription factor to facilitate its nuclear localization; SMAD4 deficiency selectively abrogated the effects of febrile temperature on Th17 cell differentiation both in vitro and ameliorated an autoimmune disease model. Our results thus demonstrate a critical role of fever in shaping adaptive immune responses with implications in autoimmune diseases.

Interleukin-27 Gene Therapy Prevents the Development of Autoimmune Encephalomyelitis but Fails to Attenuate Established Inflammation due to the Expansion of CD11b+Gr-1+ Myeloid Cells

Interleukin-27 (IL-27) and its subunit P28 (also known as IL-30) have been shown to inhibit autoimmunity and have been suggested as potential immunotherapeutic for autoimmune diseases such as multiple sclerosis (MS). However, the potential of IL-27 and IL-30 as immunotherapeutic, and their mechanisms of action have not been fully understood. In this study, we evaluated the efficacy of adeno-associated viral vector (AAV)-delivered IL-27 (AAV-IL-27) and IL-30 (AAV-IL-30) in a murine model of MS. We found that one single administration of AAV-IL-27, but not AAV-IL-30 completely blocked the development of experimental autoimmune encephalomyelitis (EAE). AAV-IL-27 administration reduced the frequencies of Th17, Treg, and GM-CSF-producing CD4+ T cells and induced T cell expression of IFN-γ, IL-10, and PD-L1. However, experiments involving IL-10-deficient mice and PD-1 blockade revealed that AAV-IL-27-induced IL-10 and PD-L1 expression were not required for the prevention of EAE development. Surprisingly, neither AAV-IL-27 nor AAV-IL-30 treatment inhibited EAE development and Th17 responses when given at disease onset. We found that mice with established EAE had significant expansion of CD11b+Gr-1+ cells, and AAV-IL-27 treatment further expanded these cells and induced their expression of Th17-promoting cytokines such as IL-6. Adoptive transfer of AAV-IL-27-expanded CD11b+Gr-1+ cells enhanced EAE development. Thus, expansion of CD11b+Gr-1+ cells provides an explanation for the resistance to IL-27 therapy in mice with established disease.

CD24 expression does not affect dopamine neuronal survival in a mouse model of Parkinson's disease

Parkinson's disease (PD) is a progressive neurodegenerative condition that is characterised by the loss of specific populations of neurons in the brain. The mechanisms underlying this selective cell death are unknown but by using laser capture microdissection, the glycoprotein, CD24 has been identified as a potential marker of the populations of cells that are affected in PD. Using in situ hybridization and immunohistochemistry on sections of mouse brain, we confirmed that CD24 is robustly expressed by many of these subsets of cells. To determine if CD24 may have a functional role in PD, we modelled the dopamine cell loss of PD in Cd24 mutant mice using striatal delivery of the neurotoxin 6-OHDA. We found that Cd24 mutant mice have an anatomically normal dopamine system and that this glycoprotein does not modulate the lesion effects of 6-OHDA delivered into the striatum. We then undertook in situ hybridization studies on sections of human brain and found-as in the mouse brain-that CD24 is expressed by many of the subsets of the cells that are vulnerable in PD, but not those of the midbrain dopamine system. Finally, we sought to determine if CD24 is required for the neuroprotective effect of Glial cell-derived neurotrophic factor (GDNF) on the dopaminergic nigrostriatal pathway. Our results indicate that in the absence of CD24, there is a reduction in the protective effects of GDNF on the dopaminergic fibres in the striatum, but no difference in the survival of the cell bodies in the midbrain. While we found no obvious role for CD24 in the normal development and maintenance of the dopaminergic nigrostriatal system in mice, it may have a role in mediating the neuroprotective aspects of GDNF in this system.

CD24 aggravates acute liver injury in autoimmune hepatitis by promoting IFN-γ production by CD4+ T cells

The T-cell-mediated immune response is implicated in many clinical hepatic injuries, such as autoimmune hepatitis and acute virus hepatitis. CD24 is widely expressed by different immune cells and plays an important role in the pathogenesis of many autoimmune diseases. However, the role of CD24 in T-cell-mediated liver injury has not been elucidated until now. Here we showed that CD24 deficiency protects mice from concanavalin A (ConA)-induced fulminant liver injury by reducing serum interferon-γ (IFN-γ) levels. CD24 expression by hepatic T cells was markedly increased following ConA challenge. Moreover, decreased IFN-γ production by hepatic CD4⁺ T cells in CD24-deficient mice was detected, which was correlated with downregulated phosphorylation of STAT1 in hepatic tissue. In vitro experiments also supported the conclusion that CD24 deficiency impaired IFN-γ production by CD4⁺ T cells following ConA, CD3/CD28 and phorbol myristate acetate/ionomycin stimulation. Our study suggests that CD24 deficiency confers hepatoprotection by decreasing CD4⁺ T-cell-dependent IFN-γ production in vivo, which suggests that CD24 might be a potential target molecule for reducing clinical hepatitis.

The CD24 surface antigen in neural development and disease

A cell's surface molecular signature enables its reciprocal interactions with the associated microenvironments in development, tissue homeostasis and pathological processes. The CD24 surface antigen (heat-stable antigen, nectadrin; small cell lung cancer antigen cluster-4) represents a prime example of a neural surface molecule that has long been known, but whose diverse molecular functions in intercellular communication we have only begun to unravel. Here, we briefly summarize the molecular fundamentals of CD24 structure and provide a comprehensive review of CD24 expression and functional studies in mammalian neural developmental systems and disease models (rodent, human). Striving for an integrated view of the intracellular signaling processes involved, we discuss the most pertinent routes of CD24-mediated signaling pathways and functional networks in neurobiology (neural migration, neurite extension, neurogenesis) and pathology (tumorigenesis, multiple sclerosis).

CD24 enrichment protects while its loss increases susceptibility of juvenile chondrocytes towards inflammation

Background

Diseases associated with human cartilage, including rheumatoid arthritis (RA) and osteoarthritis (OA) have manifested age, mechanical stresses and inflammation as the leading risk factors. Although inflammatory processes are known to be upregulated upon aging, we sought to gain a molecular understanding of how aging affects the tissue-specific response to inflammation. In this report, we explored the role of cluster of differentiation 24 (CD24) in regulating differential inflammatory responses in juvenile and adult human chondrocytes.

Methods

Differential cell-surface CD24 expression was assessed in juvenile and adult chondrocytes along with human induced pluripotent stem cell (hiPSC)-derived neonatal chondrocytes through gene expression and fluorescence-activated cell sorting (FACS) analyses. Loss of function of CD24 was achieved through silencing in chondrocytes and the effects on the response to inflammatory cues were assessed through gene expression and NFκB activity.

Results

CD24 expression in chondrocytes caused a differential response to cytokine-induced inflammation, with the CD24^high juvenile chondrocytes being resistant to IL-1ß treatment as compared to CD24^low adult chondrocytes. CD24 protects from inflammatory response by reducing NFκB activation, as an acute loss of CD24 via silencing led to an increase in NFκB activation. Moreover, the loss of CD24 in chondrocytes subsequently increased inflammatory and catabolic gene expression both in the absence and presence of IL-1ß.

Conclusions

We have identified CD24 as a novel regulator of inflammatory response in cartilage that is altered during development and aging and could potentially be therapeutic in RA and OA.

Electronic supplementary material

The online version of this article (doi:10.1186/s13075-016-1183-y) contains supplementary material, which is available to authorized users.

Association between the CD24 Ala57Val polymorphism and risk for multiple sclerosis and systemic lupus erythematosus: a meta-analysis

The cluster of differentiation 24 (CD24) Ala57Val polymorphism has been implicated as a risk factor for multiple sclerosis (MS) and systemic lupus erythematosus (SLE); however, genetic studies have produced controversial results. A meta-analysis was performed on this topic. We used odds ratio (OR) and 95% confidence interval (95% CI) to investigate the strength of association. Eleven studies from nine publications consisting of 2466 cases and 2650 controls were included. The results suggested that the CD24 Val/Val genotypes were associated with an increased risk of MS in all study subjects and Caucasians (OR = 2.28, 95% CI: 1.68–3.10, P_z < 0.001 and OR = 2.30, 95% CI: 1.66–3.20, P_z < 0.001, respectively). Sensitivity analysis showed that no individual study was found to be significantly biasing the pooled results. Although meta-analysis also suggested an association between the CD24 Val/Val genotypes and SLE risk in Caucasians (OR = 1.71, 95% CI: 1.31–2.24, P_z < 0.001), sensitivity analysis demonstrated that the association was not statistically significant after removing a Spanish study. In conclusion, this meta-analysis suggests that the CD24 Ala57Val polymorphism is associated with an increased risk of MS in Caucasians. However, the available evidence is not sufficient to support an association between the CD24 Ala57Val polymorphism and SLE risk.

CD24 Ala57Val polymorphism is associated with spontaneous viral clearance in the HCV-infected Chinese population

BACKGROUND & AIMS

Host immune response to hepatitis C virus (HCV) is a vital factor involved in both viral clearance and liver disease pathogenesis. CD24 plays an important role in inflammation and immune response and CD24 polymorphisms are associated with risk and progression of chronic hepatitis B virus infection. Our study evaluated whether CD24 polymorphisms affect HCV clearance.

METHODS

We genotyped 544 chronic hepatitis C (CHC) patients, 78 spontaneous hepatitis C clearance (SHC) patients and 215 healthy controls for CD24 gene variants at positions -P534, P170, P1527 and IFNL3 rs12979860 by pyrosequencing. In CHC patients, 362 individuals were treated with a recombinant IFN-α2b/ribavirin combination for 48 weeks and were followed up for an additional 24 weeks. Lymphocyte CD24 expression was analysed by flow cytometry.

RESULTS

We show that P170 CT and CT/TT genotypes were over-represented in the SHC group compared to CHC patients (62.8% vs. 47.2% and 75.6% vs. 60.3%, for respective polymorphisms). In multivariate logistic analysis, P170 (CD24 Ala57Val) polymorphism was an independent predictor of SHC (adjusted OR = 2.11, 95%CI = 1.19-3.73, P = 0.010 for CT genotype; OR = 2.01, 95%CI = 1.15-3.49, P = 0.014 for CT/TT genotype). No significant associations were found between the CD24 polymorphisms and treatment-induced viral clearance in log-rank analysis and Cox regression analysis. Patients with the CT/TT genotype had greater T-cell CD24 expression than patients with the CC genotype.

CONCLUSIONS

Our findings suggest that CD24 Ala57Val polymorphism and associated variations in CD24 expression may be an important predictor for SHC, but have no effect on antiviral drug treatment response in Chinese CHC patients.

Deletion of CD24 impairs development of heat shock protein gp96-driven autoimmune disease through expansion of myeloid-derived suppressor cells

CD24 binds to and suppresses inflammation triggered by danger-associated molecular patterns such as heat shock proteins (HSPs) and high-mobility group box 1. Paradoxically, CD24 has been shown to enhance autoimmune disease. In this study, we attempt to reconcile this paradox by deletion of CD24 (24KO) in a lupus-like disease model driven by forced expression of HSP gp96 at the cell surface (transgenic mice [tm]). As expected, tm24KO mice showed increased CD11c(+) dendritic cell activation coupled to a significant increase in dendritic cell-specific IL-12 production compared with tm mice. However, tm24KO mice showed less CD4 T cell activation and peripheral inflammatory cytokine production in comparison with tm mice. We characterized an enhanced immune suppressive milieu in tm24KO mice distinguished by increased TGF-β and greater regulatory T cell-suppressive capacity. We found greater absolute numbers of myeloid-derived suppressor cells (MDSCs) in tm24KO mice and showed that the Ly6C(+) MDSC subset had greater suppressive capacity from tm24KO mice. Deletion of CD24 in tm mice led to diminished lupus-like pathology as evidenced by anti-nuclear Ab deposition and glomerulonephritis. Finally, we show that expanded MDSC populations were mediated by increased free high-mobility group box 1 in tm24KO mice. Thus, the deletion of CD24 in an HSP-driven model of autoimmunity led to the unexpected development of regulatory T cell and MDSC populations that augmented immune tolerance. Further study of these populations as possible negative regulators of inflammation in the context of autoimmunity is warranted.

Role of CD24 polymorphisms in the susceptibility to inflammatory bowel disease

BACKGROUND

Inflammatory bowel disease (IBD) results from an inappropriate inflammatory response in which genetic, immune, and environmental factors all play important roles. Recently, single nucleotide polymorphisms (SNPs) in the CD24 gene have been associated with the development of several autoimmune diseases.

AIM

To evaluate whether CD24 SNPs, are associated with risk of ulcerative colitis (UC) and Crohn's disease (CD).

METHODS

The CD24 polymorphisms C170T (rs8734), TG1527del (rs3838646), A1626G (rs1058881), and A1056G (rs1058818) were assessed in a case-control study of an Israeli cohort comprising 117 IBD patients and 105 age and gender-matched healthy controls. Restriction fragment length polymorphism (RFLP) analysis was performed using BstX1, Bsr1, Mfe1, and BstU1 restriction enzymes. Odds ratios (OR) and 95% confidence intervals (CI) were estimated by logistic regression models.

RESULTS

Carriers of the C170T SNP were at increased risk of IBD (OR=3.022, 95% CI: 1.748-5.223, p=0.001), UC (OR=3.002, 95% CI: 1.661-5.427, p=0.001) and CD (OR=3.077, 95% CI: 1.334-7.095, p=0.008). Carrying the A1626G and A1056G SNPs was found to be a risk factor for IBD (OR=2.460, 95% CI: 1.420-4.259, p=0.001 and OR=1.856, 95% CI: 1.011-3.405, p=0.01), UC (OR=2.218, 95% CI: 1.207-4.075, p=0.01 and OR=1.944, 95% CI: 0.995-3.798, p=0.01) but not for CD (p=0.086 and p=0.299). The A1626G and TG1527del were found to be associated with younger age of IBD onset (p=0.022 and p=0.027, respectively).

CONCLUSIONS

The CD24 C170T polymorphism is associated with IBD risk. The A1626G and A1056G SNPs might be associated only with UC risk. These findings suggest CD24 as a new genetic susceptibility factor, with clinical implications in the prediction of IBD prognosis and therapy.

A hypermorphic SP1-binding CD24 variant associates with risk and progression of multiple sclerosis

A large number of risk alleles have been identified for multiple sclerosis (MS). However, how genetic variations may affect pathogenesis remains largely unknown for most risk alleles. Through direct sequencing of CD24 promoter region, we identified a cluster of 7 new single nucleotide polymorphisms in the CD24 promoter. A hypermorphic haplotype consisting of 3 SNPs was identified through association studies consisting of 935 control and 764 MS patients (P=0.001, odds ratio 1.3). The variant is also associated with more rapid progression of MS (P=0.016, log rank test). In cells that are heterozygous for the risk allele, chromatin immunoprecipitation revealed that risk allele specifically bind to a transcription factor SP1, which is selectively required for the hypermorphic promoter activity of the variant. In MS patients, the CD24 transcript levels associate with the SP1-binding variant in a dose-dependent manner (P=7x10(-4)). Our data revealed a potential role for SP1-mediated transcriptional regulation in MS pathogenesis.

CD24 on thymic APCs regulates negative selection of myelin antigen-specific T lymphocytes

Negative selection plays a key role in the clonal deletion of autoreactive T cells in the thymus. However, negative selection is incomplete; as high numbers of autoreactive T cells can be detected in normal individuals, mechanisms that regulate negative selection must exist. In this regard, we previously reported that CD24, a GPI-anchored glycoprotein, is required for thymic generation of autoreactive T lymphocytes. The CD24-deficient 2D2 TCR transgenic mice (2D2(+) CD24(-/-) ), whose TCR recognizes myelin oligodendrocyte glycoprotein (MOG), fail to generate functional 2D2 T cells. However, it was unclear if CD24 regulated negative selection, and if so, what cellular mechanisms were involved. Here, we show that elimination of MOG or Aire gene expression in 2D2(+) CD24(-/-) mice - through the creation of 2D2(+) CD24(-/-) MOG(-/-) or 2D2(+) CD24(/) ∼Aire(-/-) mice - completely restores thymic cellularity and function of 2D2 T cells. Restoration of CD24 expression on DCs, but not on thymocytes also partially restores 2D2 T-cell generation in 2D2(+) CD24(-/-) mice. Taken together, we propose that CD24 expression on thymic antigen-presenting cells (mTECs, DCs) down-regulates autoantigen-mediated clonal deletion of autoreactive thymocytes.

CD24 gene allele variation is not associated with oligoclonal IgG bands and IgG index of multiple sclerosis patients

OBJECTIVE

Multiple sclerosis (MS) shows evidence of many distinctive aspects of an autoimmune disorder, including a polygenic inheritance. A recent candidate gene for susceptibility to MS is CD24, which has also been shown to be associated with disease progression. This study was designed to examine whether there is a relationship between the CD24 genotype, oligoclonal band (OCB) status and IgG index in the cerebrospinal fluid (CSF) of MS patients.

METHODS

A total of 27 definite MS patients were enrolled in this cross-sectional study. Blood samples were collected from a peripheral vein, and CSF was obtained by lumbar puncture. The CD24 gene was sequenced in the blood specimen, and albumin and IgG concentrations were measured in both CSF and serum. We compared both IgG index and OCB status in patients with and without CD24V/V. The correlation between MS severity score (MSSS), OCB status, CD24 genotype and IgG index was studied.

RESULTS

Only 15 patients were OCB positive. Among patients with negative OCBs, only 2 patients had the V/V genotype. Furthermore, in those with the V/V genotype, IgG index was not significantly elevated (p = 0.322). Patients with the V/V genotype had a significantly higher MSSS (p = 0. 04), but neither the presence of OCBs nor the IgG index showed significant correlation with MSSS (p = 0.379 and 0.20, respectively).

CONCLUSION

We could not show any relationship between the CD24V/V genotype, OCB status and IgG index. This could be interpreted as indicating that the CD24V/V allele exerts its effects on the disease course independently of CSF IgG synthesis.

Laquinimod suppress antigen presentation in relapsing-remitting multiple sclerosis: in-vitro high-throughput gene expression study

Laquinimod (LAQ) is a new immunomodulatory drug shown to be effective in the treatment of relapsing-remitting multiple sclerosis (RRMS); however, its molecular target pathways are not well recognized. In this study we characterized in-vitro the molecular effects of LAQ in peripheral blood mononuclear cells (PBMC) of healthy subjects and RRMS patients by gene expression microarrays. We demonstrated that LAQ induced suppression of genes related to antigen presentation and corresponding inflammatory pathways. These findings were demonstrated mainly via the NFkB pathway. Analysis of PBMC subpopulations identified activation of Th2 response in CD14+ and CD4+ cells and suppression of proliferation in CD8+ cells.

CD24: from A to Z

As a testament to the importance of CD24, researchers with diverse interests, including adaptive immunity, inflammation, autoimmune diseases and cancer, have encountered CD24. CD24 is overexpressed in many cancers and appears oncogenic. In the adaptive immune response, CD24 is a redundant costimulatory molecule in costimulation-rich lymphoid organs but is essential in selected target organs tested, such as brain and skin. More recent studies suggest it may have a role in discriminating danger and pathogen-associated molecular patterns by dendritic cells. The biology of CD24 is intriguing but poorly understood. Here we summarize the major findings associated with CD24 to stimulate new ideas for further research that may reveal the underlying link among the diverse processes mediated by CD24.

CD24-Siglec G/10 discriminates danger- from pathogen-associated molecular patterns

It is now well accepted that the innate immune system recognizes both damage (or danger)- and pathogen-associated molecular patterns (DAMP and PAMP, respectively) through pattern recognition receptors, such as Toll-like receptors (TLR) and/or Nod-like receptors (NLR). Less clear are whether and how the response to PAMP and DAMP are regulated differentially. The answers may reveal whether the primary goal of the immune system is to defend against infections or to alert the host of tissue injuries. We demonstrated recently that the host response to DAMP is controlled by a DAMP-CD24-Siglec axis. Here we propose a key role for the CD24-Siglec pathway in discriminating between DAMPs and PAMPs.

CD24 polymorphisms affect risk and progression of chronic hepatitis B virus infection

T-cell immunity to hepatitis B virus (HBV) is involved in both viral clearance and the pathogenesis of cirrhosis and hepatocellular carcinoma following chronic HBV infection. It is therefore of great interest to analyze whether genetic polymorphism of genes involved in the immune response may determine the outcomes of chronic HBV infection. Here we report that CD24 polymorphisms affect the risk and progression of chronic HBV infection. Thus the CD24 P170(T) allele, which is expressed at a higher level, is associated with an increased risk of chronic HBV infection. Among the chronic HBV patients this allele shows recessive association with more rapid progression to liver cirrhosis and hepatocellular carcinoma in comparison to the P170(C) allele. In contrast, a dinucleotide deletion at position 1527-1528 (P1527(del)), which reduces CD24 expression, is associated with a significantly reduced risk of chronic HBV infection. To confirm the role for CD24 in liver carcinogenesis, we compared the size of liver tumor developed in CD24(-/-) and CD24(+/-) HBV transgenic mice. Our data demonstrate that targeted mutation of CD24 drastically reduced the sizes of spontaneous liver cancer in the HBV transgenic mice.

CONCLUSION

These data demonstrate that genetic variation of CD24 may be an important determinant for the outcome of chronic HBV infection.

CD24 and Siglec-10 selectively repress tissue damage-induced immune responses

Patten recognition receptors, which recognize pathogens or components of injured cells (danger), trigger activation of the innate immune system. Whether and how the host distinguishes between danger- versus pathogen-associated molecular patterns remains unresolved. We report that CD24-deficient mice exhibit increased susceptibility to danger- but not pathogen-associated molecular patterns. CD24 associates with high mobility group box 1, heat shock protein 70, and heat shock protein 90; negatively regulates their stimulatory activity; and inhibits nuclear factor kappaB (NF-kappaB) activation. This occurs at least in part through CD24 association with Siglec-10 in humans or Siglec-G in mice. Our results reveal that the CD24-Siglec G pathway protects the host against a lethal response to pathological cell death and discriminates danger- versus pathogen-associated molecular patterns.

The genetics of clinical outcome in multiple sclerosis

Multiple sclerosis (MS) is a common inflammatory disease of the central nervous system (CNS), the clinical course of which varies considerably between patients. Genetic complexity and interactions with as yet unknown environmental factors have hindered researchers from fully elucidating the aetiology of the disease. In addition to influencing disease susceptibility, epidemiological evidence suggests that genetic factors may affect phenotypic expression of the disease. Genes that affect clinical outcome may be more effective therapeutic targets than those which determine susceptibility. We present in this review a comprehensive survey of the genes (both MHC- and non-MHC-related) that have been investigated for their role in disease outcome in MS. Recent studies implicating the role of the genotype and epistatic interactions in the MHC in determining outcome are highlighted.

A 9-centimorgan interval of chromosome 10 controls the T cell-dependent psoriasiform skin disease and arthritis in a murine psoriasis model

Psoriasis is a complex genetic disease of unresolved pathogenesis with both heritable and environmental factors contributing to onset and severity. In addition to a disfiguring skin inflammation, approximately 10-40% of psoriasis patients suffer from destructive joint involvement. Previously, we reported that the CD18 hypomorphic PL/J mouse carrying a mutation resulting in reduced expression of the common chain of beta(2) integrins (CD11/CD18) spontaneously develops a skin disease that closely resembles human psoriasis. In contrast, the same mutation on C57BL/6J background did not demonstrate this phenotype. By a genome-wide linkage analysis, two major loci were identified as contributing to the development of psoriasiform dermatitis under the condition of low CD18 expression. Using a congenic approach, we now demonstrate that the introduction of a 9-centimorgan fragment of chromosome 10 derived from the PL/J strain into the disease-resistant CD18 hypomorphic C57BL/6J was promoting the development of psoriasiform skin disease and notably also arthritis. We therefore designated this locus psoriasiform skin disease-associated locus 1 (PSD1). High numbers of CD4(+) T cells and TNF-alpha producing macrophages were detected both in inflamed skin and joints in these congenic mice, with a complete resolution upon TNF-alpha inhibitor therapy or depletion of CD4(+) T cells. For the first time, we have identified a distinct genetic element that contributes to the T cell-dependent development of both psoriasiform skin disease and associated arthritis. This congenic model will be suitable to further investigations of genetic and molecular pathways that cause psoriasiform dermatitis and arthritis, and it may also be relevant for other autoimmune diseases.

Association of a CD24 gene polymorphism with susceptibility to systemic lupus erythematosus

OBJECTIVE

To determine the potential role of the CD24 A57V gene polymorphism in systemic lupus erythematosus (SLE).

METHODS

We studied 3 cohorts of Caucasian patients and controls. The Spanish cohort included 696 SLE patients and 539 controls, the German cohort included 257 SLE patients and 317 controls, and the Swedish cohort included 310 SLE patients and 247 controls. The CD24 A57V polymorphism was genotyped by polymerase chain reaction, using a predeveloped TaqMan allele discrimination assay. Odds ratios (ORs) and 95% confidence intervals (95% CIs) were calculated.

RESULTS

In the Spanish cohort there was a statistically significant difference in the distribution of the CD24 V allele between SLE patients and controls (OR 3.6 [95% CI 2.13-6.16], P < 0.0001). In addition, frequency of the CD24 V/V genotype was increased in SLE patients compared with controls (OR 3.7 [95% CI 2.16-6.34], P < 0.00001). We sought to replicate this association with SLE in a German population and a Swedish population. A similar trend was found in the German group. The CD24 V/V genotype and the CD24 V allele were more frequent in SLE patients than in controls, although this difference was not statistically significant. No differences were observed in the Swedish group. A meta-analysis of the Spanish and German cohorts demonstrated that the CD24 V allele has a risk effect in SLE patients (pooled OR 1.25 [95% CI 1.08-1.46], P = 0.003). In addition, homozygosity for the CD24 V risk allele significantly increased the effect (pooled OR 2.19 [95% CI 1.50-3.22], P = 0.00007).

CONCLUSION

These findings suggest that the CD24 A57V polymorphism plays a role in susceptibility to SLE in a Spanish population.

CD24: a genetic checkpoint in T cell homeostasis and autoimmune diseases

CD24 is widely used as a marker for differentiation of multiple lineages of cells and can provide costimulation for T cells, especially in non-lymphoid target organs. Recent studies demonstrate that CD24 controls an important genetic checkpoint for homeostasis and autoimmune diseases in both mice and humans. Understanding the molecular and cellular basis of CD24 function could provide important insights into T cell biology and autoimmunity.

CD24 on the Resident Cells of the Central Nervous System Enhances Experimental Autoimmune Encephalomyelitis

CD24 is a cell surface glycoprotein that is expressed on both immune cells and cells of the CNS. We have previously shown that CD24 is required for the induction of experimental autoimmune encephalomyelitis (EAE), an experimental model for the human disease multiple sclerosis (MS). The development of EAE requires CD24 expression on both T cells and non-T host cells in the CNS. To understand the role of CD24 on the resident cells in the CNS during EAE development, we created CD24 bone marrow chimeras and transgenic mice in which CD24 expression was under the control of a glial fibrillary acidic protein promotor (AstroCD24TG mice). We showed that mice lacking CD24 expression on the CNS resident cells developed a mild form of EAE; in contrast, mice with overexpression of CD24 in the CNS developed severe EAE. Compared with nontransgenic mice, the CNS of AstroCD24TG mice had higher expression of cytokine genes such as IL-17 and demyelination-associated marker P8; the CNS of AstroCD24TG mice accumulated higher numbers of Th17 and total CD4+ T cells, whereas CD4+ T cells underwent more proliferation during EAE development. Expression of CD24 in CD24-deficient astrocytes also enhanced their costimulatory activity to myelin oligodendrocyte glycoprotein-specific, TCR-transgenic 2D2 T cells. Thus, CD24 on the resident cells in the CNS enhances EAE development via costimulation of encephalitogenic T cells. Because CD24 is increased drastically on resident cells in the CNS during EAE, our data have important implications for CD24-targeted therapy of MS.

A dinucleotide deletion in CD24 confers protection against autoimmune diseases

It is generally believed that susceptibility to both organ-specific and systemic autoimmune diseases is under polygenic control. Although multiple genes have been implicated in each type of autoimmune disease, few are known to have a significant impact on both. Here, we investigated the significance of polymorphisms in the human gene CD24 and the susceptibility to multiple sclerosis (MS) and systemic lupus erythematosus (SLE). We used cases/control studies to determine the association between CD24 polymorphism and the risk of MS and SLE. In addition, we also considered transmission disequilibrium tests using family data from two cohorts consisting of a total of 150 pedigrees of MS families and 187 pedigrees of SLE families. Our analyses revealed that a dinucleotide deletion at position 1527∼1528 (P1527^del) from the CD24 mRNA translation start site is associated with a significantly reduced risk (odds ratio = 0.54 with 95% confidence interval = 0.34–0.82) and delayed progression (p = 0.0188) of MS. Among the SLE cohort, we found a similar reduction of risk with the same polymorphism (odds ratio = 0.38, confidence interval = 0.22–0.62). More importantly, using 150 pedigrees of MS families from two independent cohorts and the TRANSMIT software, we found that the P1527^del allele was preferentially transmitted to unaffected individuals (p = 0.002). Likewise, an analysis of 187 SLE families revealed the dinucleotide-deleted allele was preferentially transmitted to unaffected individuals (p = 0.002). The mRNA levels for the dinucleotide-deletion allele were 2.5-fold less than that of the wild-type allele. The dinucleotide deletion significantly reduced the stability of CD24 mRNA. Our results demonstrate that a destabilizing dinucleotide deletion in the 3′ UTR of CD24 mRNA conveys significant protection against both MS and SLE.

When an individual's immune system attacks self tissues or organs, he/she develops autoimmune diseases. Although it is well established that multiple genes control susceptibility to autoimmune diseases, most of the genes remain unidentified. In addition, although different autoimmune diseases have a common immunological basis, a very small number of genes have been identified that affect multiple autoimmune diseases. Here we show that a variation in CD24 is a likely genetic factor for the risk and progression of two types of autoimmune diseases, including multiple sclerosis (MS), an organ-specific autoimmune disease affecting the central nervous system, and systemic lupus erythematosus, a systemic autoimmune disease. Our data indicated that if an individual's CD24 gene has a specific two-nucleotide deletion in the noncoding region of CD24 mRNA, his/her risk of developing MS or SLE is reduced by 2- to 3-fold. As a group, MS patients with the two-nucleotide deletion will likely have a slower disease progression. Biochemical analysis indicated that the deletion leads to rapid decay of CD24 mRNA, which should result in reduced synthesis of the CD24 protein. Our data may be useful for the treatment and diagnosis of autoimmune diseases.

CD62L is required for the priming of encephalitogenic T cells but does not play a major role in the effector phase of experimental autoimmune encephalomyelitis

CD62L (l-selectin, mel 14) regulates naïve T cell homing into lymph nodes and the migration of leucocytes to sites of inflammation. The requirement of CD62L in the pathogenesis of experimental autoimmune encephalomyelitis (EAE), an animal model of multiple sclerosis, has been demonstrated previously. However, it remains controversial as to whether CD62L is required for the induction or the effector phase of EAE. It is also unclear whether other non-T effector cells need CD62L to enter the central nervous system (CNS) parenchyma and exert their damaging effects on myelin. We report that mice with a targeted mutation of CD62L are resistant to Myelin oligodendrocyte glycoprotein peptide-induced EAE. CD62L-deficient mice had no peptide-specific T cell responses in the draining lymph nodes and had lower levels of peptide-specific T cell responses in spleens at a later time point. Adoptive transfer studies showed that CD62L-deficient mice were fully susceptible to adoptive transfer EAE induced by either wildtype or CD62L-deficient T cells. Moreover, CD62L-deficient, F4/80(+) macrophages can be efficiently recruited into the CNS parenchyma. These data suggest that CD62L is required for the induction of encephalitogenic T cells during EAE development, but is not required by T and non-T effector cells to attack the CNS parenchyma.

Massive and destructive T cell response to homeostatic cue in CD24-deficient lymphopenic hosts

In response to a lymphopenic cue, T lymphocytes undergo a slow-paced homeostatic proliferation in an attempt to restore T cell cellularity. The molecular interaction that maintains the pace of homeostatic proliferation is unknown. In this study, we report that in lymphopenic CD24-deficient mice, T cells launch a massive proliferation that results in the rapid death of the recipient mice. The dividing T cells have phenotypes similar to those activated by cognate antigens. The rapid homeostatic proliferation is caused by a lack of CD24 on dendritic cells (DCs). Interestingly, although CD24 expression in T cells is required for optimal homeostatic proliferation in the wild-type (WT) host, mice lacking CD24 on all cell types still mount higher homeostatic proliferation than the WT mice. Thus, a lack of CD24 in the non–T host cells bypassed the requirement for T cell expression of CD24 in homeostatic proliferation in the WT host. Our data demonstrate that CD24 expressed on the DCs limits T cell response to homeostatic cue and prevents fatal damage associated with uncontrolled homeostatic proliferation.

CD24 Ala/Val polymorphism and multiple sclerosis

CD24 is expressed on a broad range of cells in the immune and central nervous systems and appears to be required for development of experimental autoimmune encephalomyelitis in mice. Association of a CD24 Ala/Val coding polymorphism with susceptibility to and progression of multiple sclerosis was recently reported. We typed this coding polymorphism in a combined cohort of 1,180 cases and 1,168 unrelated and family-based controls from Belgium and the UK, but were unable to confirm either association. Since the CD24 gene is part of a segmental duplication, special care is required for the identification and genotyping of single nucleotide polymorphisms.

B7-1-HSA (CD80-CD24), a recombinant hybrid costimulatory molecule retains ligand binding and costimulatory functions

Optimal activation of naïve T lymphocyte requires two signals; an antigen-specific signal initiated by engagement of TCR with the antigen-MHC complex and a costimulatory signal independent of the antigen receptor complex. Without the costimulatory signal, T cells become anergic. Various adhesion molecules, such as B7-1 (CD80) and heat stable antigen (HSA, CD24), expressed on antigen presenting cells have been demonstrated to provide costimulatory signals to T cells. It was reported that the combinations of different adhesion molecules could induce even stronger immune response. In this study, we made a hybrid costimulatory molecule, B7-1-HSA, and tested its T cell stimulatory function. Chinese hamster ovary (CHO) cells expressing this hybrid molecule bound both anti-CD80 and anti-CD24 monoclonal antibodies, and induced stronger T cell proliferation than CHO cells expressing B7-1 or HSA alone. These results suggest that the B7-1-HSA hybrid molecule can deliver two costimulatory signals simultaneously that can synergize in inducing T cell proliferation. The purified B7-1-HSA protein reacted with both anti-B7-1 and anti-HSA mAbs in Western blotting and specifically mediated adhesion of Jurkat cells. Furthermore, purified B7-1-HSA molecule spontaneously incorporated onto cell membrane through its glycolipid anchor suggesting that this hybrid costimulatory molecule can be used in protein transfer to develop effective cancer vaccines.

Differential effects of IL-21 during initiation and progression of autoimmunity against neuroantigen

The cytokine IL-21 is closely related to IL-2 and IL-15, a cytokine family that uses the common gamma-chain for signaling. IL-21 is expressed by activated CD4(+) T cells. We examined the role of IL-21 in the autoimmune disease experimental autoimmune encephalomyelitis (EAE), an animal model for human multiple sclerosis. IL-21 administration before induction of EAE with a neuroantigen, myelin oligodendrocyte glycoprotein peptide 35-55, and adjuvant enhanced the inflammatory influx into the CNS, as well as the severity of EAE. Autoreactive T cells purified from IL-21-treated mice transferred more severe EAE than did the control encephalitogenic T cells. No such effects were observed when IL-21 was administered after EAE progressed. Additional studies demonstrated that IL-21 given before the induction of EAE boosted NK cell function, including secretion of IFN-gamma. Depletion of NK cells abrogated the effect of IL-21. Therefore, IL-21, by affecting NK cells, has differential effects during the initiation and progression of autoimmune responses against neuroantigens.