Pathways: Strategies for susceptibility genes in SLE

The pentraxin family in autoimmune disease

The pentraxins represent a family of multifunctional proteins composed of long and short pentamers. The latter includes serum amyloid P component (SAP) and C-reactive protein (CRP) whereas the former includes neuronal PTX1 and PTX2 (NPTX1 and NPTX2, respectively), PTX3 and PTX4. These serve as a bridge between adaptive immunity and innate immunity and a link between inflammation and immunity. Similarities and differences between long and short pentamers are examined and their roles in autoimmune disease are discussed. Increased CRP and PTX3 could indicate the activity of rheumatoid arthritis, systemic lupus erythematosus or other autoimmune diseases. Mechanistically, CRP and PTX3 may predict target organ injury, regulate bone metabolic immunity and maintain homeostasis as well as participate in vascular endothelial remodeling. Interestingly, PTX3 is pleiotropic, being involved in inflammation and tissue repair. Given the therapeutic potential of PTX3 and CRP, targeting these factors to exert a beneficial effect is the focus of research efforts. Unfortunately, studies on NPTX1, NPTX2, PTX4 and SAP are scarce and more research is clearly needed to elaborate their potential roles in autoimmune disease.

Dioscin ameliorates silica-aggravated systemic lupus erythematosus via suppressing apoptosis and improving LC3-associated phagocytosis in MRL/lpr mice

Inhalation of silica not only directly leads to silicosis locally, but also results in various types of autoimmune diseases systemically, most commonly systemic lupus erythematosus (SLE). Little is known about the etiopathogenesis of silica-aggravated SLE to date, however, abnormal apoptosis and impaired apoptotic clearance have been reported to be closely related to the occurrence of SLE. LC3-associated phagocytosis (LAP) is a non-canonical form of autophagy, which plays a crucial role in mediating the clearance of apoptotic cells. Here we showed that the excessive accumulation of apoptotic debris in MRL/lpr mice exposed to silica might be due to the increased cell apoptosis and defective LAP caused by silica, thus accelerating the occurrence and progression of silica-aggravated SLE. Dioscin is an active ingredient in the family of Dioscoreaceae and is reported to possess multiple pharmacological activities, including anti-inflammatory, anti-apoptotic and autophagy-promoting properties. However, its role in SLE aggravated by silica exposure has not been investigated. In our study, we confirmed that dioscin decreased the accumulation of apoptotic debris by suppressing the excessive cell apoptosis and improving the LAP of immune cells in lung and spleen, leading to subsequent dramatically ameliorated lupus-like symptoms in silica-exposed MRL/lpr mice.

Lupus Nephritis: Current Perspectives and Moving Forward

Lupus nephritis is a severe organ manifestation of systemic lupus erythematosus, and its pathogenesis involves complex etiology and mechanisms. Despite significant knowledge gains and extensive efforts put into understanding the development and relapsing disease activity, lupus nephritis remains a substantial cause of morbidity and mortality in lupus patients. Current therapies retain a significant unmet medical need regarding rates of complete response, preventing relapse of lupus nephritis, progression of chronic kidney disease to kidney failure, drug toxicity, and pill burden-related drug non-adherence. Connected to progression of chronic kidney disease are the associated risks for disabling or even lethal cardiovascular events, as well as chronic kidney disease-related secondary immunodeficiency and serious infections. In this regard, biomarkers are needed that can predict treatment response to specific drugs to enable personalized precision medicine. A series of clinical trials with innovative immunomodulatory drugs are ongoing and raise expectations for improvements in the management of lupus nephritis. Here, we review how new developments in pathogenesis connect with current and future perspectives for the management of lupus nephritis.

Upregulation of FcγRIIB by resveratrol via NF-κB activation reduces B-cell numbers and ameliorates lupus

Resveratrol, an anti-inflammatory agent, can inhibit pro-inflammatory mediators by activating Sirt1, which is a class III histone deacetylase. However, whether resveratrol can regulate inhibitory or anti-inflammatory molecules has been less studied. FcγRIIB, a receptor for IgG, is an essential inhibitory receptor of B cells for blocking B-cell receptor-mediated activation and for directly inducing apoptosis of B cells. Because mice deficient in either Sirt1 or FcγRIIB develop lupus-like diseases, we investigated whether resveratrol can alleviate lupus through FcγRIIB. We found that resveratrol enhanced the expression of FcγRIIB in B cells, resulting in a marked depletion of plasma cells in the spleen and notably in the bone marrow, thereby decreasing serum autoantibody titers in MRL/lpr mice. The upregulation of FcγRIIB by resveratrol involved an increase of Sirt1 protein and deacetylation of p65 NF-κB (K310). Moreover, increased binding of phosphor-p65 NF-κB (S536) but decreased association of acetylated p65 NF-κB (K310) and phosphor-p65 NF-κB (S468) to the −480 promoter region of Fcgr2b gene was responsible for the resveratrol-mediated enhancement of FcγRIIB gene transcription. Consequently, B cells, especially plasma cells, were considerably reduced in MRL/lpr mice, leading to improvement of nephritis and prolonged survival. Taken together, we provide evidence that pharmacological upregulation of FcγRIIB expression in B cells via resveratrol can selectively reduce B cells, decrease serum autoantibodies and ameliorate lupus nephritis. Our findings lead us to propose FcγRIIB as a new target for therapeutic exploitation, particularly for lupus patients whose FcγRIIB expression levels in B cells are downregulated.

Genetics of Lupus Nephritis: Clinical Implications

Systemic lupus erythematosus is a heterogeneous autoimmune disease marked by the presence of pathogenic autoantibodies, immune dysregulation, and chronic inflammation that may lead to increased morbidity and early mortality from end-organ damage. More than half of all systemic lupus erythematosus patients will develop lupus nephritis. Genetic-association studies have identified more than 50 polymorphisms that contribute to lupus nephritis pathogenesis, including genetic variants associated with altered programmed cell death and defective immune clearance of programmed cell death debris. These variants may support the generation of autoantibody-containing immune complexes that contribute to lupus nephritis. Genetic variants associated with lupus nephritis also affect the initial phase of innate immunity and the amplifying, adaptive phase of the immune response. Finally, genetic variants associated with the kidney-specific effector response may influence end-organ damage and the progression to end-stage renal disease and death. This review discusses genetic insights of key pathogenic processes and pathways that may lead to lupus nephritis, as well as the clinical implications of these findings as they apply to recent advances in biologic therapies.

Preliminary genomic survey and sequence analysis of the complement system in non-eutherian mammals

The complement system is a major mediator of the vertebrate immune system, which functions in both innate and specific immune responses. It comprises more than 30 proteins working to remove foreign cells by way of anaphylatoxins, opsonins or the membrane attack complex. Over the last few years, whole genome sequences of non-eutherian mammals (marsupials and a monotreme), the gray short-tailed opossum (Monodelphis domestica), tammar wallaby (Macropus eugenii), Tasmanian devil (Sarcophilus harrisii), koala (Phascolarctos cinereus) and platypus (Ornithorhynchus anatinus), have become publicly available. Using these sequences, we have identified an array of complement components in non-eutherians using online search tools and algorithms. Of 57 complement and complement-related genes investigated, we identified 46 in the gray short-tailed opossum genome, 27 in the tammar wallaby genome, 44 in the Tasmanian devil genome, 47 in the koala genome and 40 in the platypus genome. The results of this study confirm the presence of key complement components in the immune repertoire of non-eutherian mammals and provide a platform for future studies on immune protection in young marsupials.

Clinical perspectives on lupus genetics: advances and opportunities

In recent years, genome-wide association studies have led to an expansion in the identification of regions containing confirmed genetic risk variants within complex human diseases, such as systemic lupus erythematosus (SLE). Many of the strongest SLE genetic associations can be divided into groups based on their potential roles in different processes implicated in lupus pathogenesis, including ubiquitination, DNA degradation, innate immunity, cellular immunity, lymphocyte development, and antigen presentation. Recent advances have also shown several genetic associations with SLE subphenotypes and subcriteria. Many areas for further exploration remain to move lupus genetic studies toward clinically informative end points.

Evaluation of SLE Susceptibility Genes in Malaysians

Systemic Lupus Erythematosus (SLE) is a clinically heterogeneous autoimmune disease with strong genetic and environmental components. Our objective was to replicate 25 recently identified SLE susceptibility genes in two distinct populations (Chinese (CH) and Malays (MA)) from Malaysia. We genotyped 347 SLE cases and 356 controls (CH and MA) using the ImmunoChip array and performed an admixture corrected case-control association analysis. Associated genes were grouped into five immune-related pathways. While CH were largely homogenous, MA had three ancestry components (average 82.3% Asian, 14.5% European, and 3.2% African). Ancestry proportions were significantly different between cases and controls in MA. We identified 22 genes with at least one associated SNP (P < 0.05). The strongest signal was at HLA-DRA (P_Meta = 9.96 × 10⁻⁹; P_CH = 6.57 × 10⁻⁸, P_MA = 6.73 × 10⁻³); the strongest non-HLA signal occurred at STAT4 (P_Meta = 1.67 × 10⁻⁷; P_CH = 2.88 × 10⁻⁶, P_MA = 2.99 × 10⁻³). Most of these genes were associated with B- and T-cell function and signaling pathways. Our exploratory study using high-density fine-mapping suggests that most of the established SLE genes are also associated in the major ethnicities of Malaysia. However, these novel SNPs showed stronger association in these Asian populations than with the SNPs reported in previous studies.

The CD11b-integrin (ITGAM) and systemic lupus erythematosus

Variations at the ITGAM gene, which encodes for the CD11b chain of the Mac-1 (alphaMbeta2; CD11b/CD18; complement receptor-3) integrin, is one of the strongest genetic risk factors for systemic lupus erythematosus (SLE). More specifically, a genetic variant (rs1143679) which results in an arginine to histidine substitution at position 77 in the extracellular portion of the integrin is associated with disease. It has recently been shown that this amino acid substitution results in a dysfunctional integrin, which is deficient in mediating cell adhesion to integrin ligands, phagocytosis and in addition cannot restrict inflammatory cytokine production in macrophages. In this review, we discuss immunological functions of the Mac-1 integrin and how defects in the genetic variant of Mac-1 may relate to SLE development.

Multiple lupus-associated ITGAM variants alter Mac-1 functions on neutrophils

OBJECTIVE

Multiple studies have demonstrated that single-nucleotide polymorphisms (SNPs) in the ITGAM locus (including the nonsynonymous SNPs rs1143679, rs1143678, and rs1143683) are associated with systemic lupus erythematosus (SLE). ITGAM encodes the protein CD11b, a subunit of the β2 integrin Mac-1. The purpose of this study was to determine the effects of ITGAM genetic variation on the biologic functions of neutrophil Mac-1.

METHODS

Neutrophils from ITGAM-genotyped and -sequenced healthy donors were isolated for functional studies. The phagocytic capacity of neutrophil ITGAM variants was probed with complement-coated erythrocytes, serum-treated zymosan, heat-treated zymosan, and IgG-coated erythrocytes. The adhesion capacity of ITGAM variants, in adhering to either purified intercellular adhesion molecule 1 or tumor necrosis factor α-stimulated endothelial cells, was assessed in a flow chamber. Expression levels of total CD11b and activation of CD11b were assessed by flow cytometry.

RESULTS

Mac-1-mediated neutrophil phagocytosis, determined in cultures with 2 different complement-coated particles, was significantly reduced in individuals with nonsynonymous variant alleles of ITGAM. This reduction in phagocytosis was related to variation at either rs1143679 (in the β-propeller region) or rs1143678/rs1143683 (highly linked SNPs in the cytoplasmic/calf-1 regions). Phagocytosis mediated by Fcγ receptors was also significantly reduced in donors with variant ITGAM alleles. Similarly, firm adhesion of neutrophils was significantly reduced in individuals with variant ITGAM alleles. These functional alterations were not attributable to differences in total receptor expression or activation.

CONCLUSION

The nonsynonymous ITGAM variants rs1143679 and rs1143678/rs113683 contribute to altered Mac-1 function on neutrophils. These results underscore the need to consider multiple nonsynonymous SNPs when assessing the functional consequences of ITGAM variation on immune cell processes and the risk of SLE.

Decreased ITGAM and FcγRIIIA mRNA expression levels in peripheral blood mononuclear cells from patients with systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is a multisystem autoimmune disease with complex genetic predisposing factors involved. ITGAM and FCγRIIIA are two kinds of immune complex clearance molecules. The variants in ITGAM and FCγRIIIA genes have been confirmed to be associated with SLE. The aim of this study is to investigate the association of mRNA expression levels of ITGAM and FCγRIIIA with SLE. Real-time transcription-polymerase chain reaction analysis (RT-PCR) was used to determine the expression levels of ITGAM and FCγRIIIA mRNA in peripheral blood mononuclear cells (PBMC) from 60 patients with SLE and 60 healthy controls. Flow cytometry was used to measure the expression level of ITGAM and FcγRIIIA from 30 SLE patients and 30 healthy controls. The expression levels of ITGAM mRNA was significantly decreased in SLE patients compared with healthy controls (P = 0.007). Patients with arthritis had higher ITGAM mRNA level than those without arthritis (P = 0.029). The expression level of FCγRIIIA mRNA in SLE patients was significantly lower than that of healthy controls (P = 0.001). Decreased expression level of FCγRIIIA mRNA was also found in patients with LN compared with those without LN (P = 0.015). The level of ITGAM mRNA in patients with anti-SSB positive, anti-RNP positive, complement reduction and increased IgG was significantly reduced. No significant correlation was found between ITGAM and FcγRIIIA mRNA expression level in SLE patients (r = -0.019, P = 0.882). Expression of ITGAM protein in T cells, neutrophil and monocyte of SLE patients was significantly lower than healthy controls (P < 0.05). For FcγRIIIA protein expression in monocyte and NK cells, there were no significant difference between SLE patients and healthy controls (P > 0.05). The altered expression levels of ITGAM and FCγRIIIA mRNA in SLE patients and their correlations with clinical data suggest that ITGAM and FCγRIIIA may play a role in this disease.

Association study of CRP gene in systemic sclerosis in European Caucasian population

Opsonization and apoptotic cell elements are critical in systemic lupus erythematosus (SLE) and could act through the activation of the innate immunity. C-reactive protein (CRP) belongs to opsonins, and polymorphisms of CRP gene have been shown to be associated with SLE susceptibility. Accumulating evidences show that SLE and systemic sclerosis (SSc) share some genetic susceptibility factors. To determine whether polymorphisms of CRP confer susceptibility to SSc, four SNPs (rs1130864, rs1205, rs1800947 and rs1341665), chosen using Hapmap linkage disequilibrium data and published data, were genotyped in a cohort of 651 SSc patients (569 with antinuclear antibodies, 258 with anti-centromere and 153 with anti-topoisomerase I) and 442 controls. All individuals were of French Caucasian origin. The four polymorphisms were in Hardy-Weinberg equilibrium in the control population. Allelic and genotypic frequencies for these four polymorphisms were found to be similar in SSc patients and controls. Moreover, subphenotype analyses in particular for subgroups having antinuclear antibodies did not detect any difference between SSc patients and controls. These results obtained through a large cohort of European Caucasian SSc patients do not support the implication of CRP gene in the pathogenesis of SSc.

A study on anti-mannose binding lectin (anti-MBL) antibodies and serum MBL levels in Indian systemic lupus erythematosus patients

Systemic lupus erythematosus (SLE) is a prototype autoimmune disease characterized by systemic inflammation and autoantibody production. Anti-MBL autoantibodies have been studied in SLE for their possible effect on MBL levels and functional activity. This study aimed at detection of anti-MBL autoantibodies in Indian SLE patients and evaluates their relationship with related immunological parameters. Two hundred diagnosed SLE patients from Western India were included in the study where 87 patients were lupus nephritis (LN) (43.5 %) and remaining (56.5 %) were non-LN. Disease activity was assessed using the Systemic Lupus Erythematosus Disease Activity Index (SLEDAI). Anti-MBL autoantibodies to IgG and IgM isotypes, anti-C1q autoantibodies, MBL levels and circulating immune complex levels were detected by ELISA. C3, C4 and CRP levels were detected by nephelometer. Anti-MBL autoantibodies were detected in 52 % SLE patients, where 55 % had IgG-anti-MBL, 33.8 % had IgM-anti-MBL and 11.3 % had both subclasses. Low MBL levels were present in 64.4 % anti-MBL positives as compared with 61.5 % in anti-MBL negatives. Among anti-MBL positives, 74 % had anti-C1q antibodies, whereas 41.7 % of anti-MBL negatives had anti-C1q autoantibodies (p = 3.45E06). An inverse correlation was observed between serum MBL and CIC levels. A statistically significant difference was noted between anti-MBL positives and anti-MBL negative patients with hsCRP levels (p = 0.002). Occurrence of infections was higher among anti-MBL positives (65 %) as compared with anti-MBL negatives (35 %). The difference between SLEDAI scores among anti-MBL positive and negative groups was statistically insignificant. Anti-MBL autoantibodies in SLE patients can influence functional activity of MBL and have a significant role in SLE disease pathogenesis.

Anti-C1q antibodies and their association with complement components in Indian systemic lupus erythematosus patients

Systemic lupus erythematosus (SLE) is a prototype autoimmune disease, characterized by immune complex formation and systemic inflammation. Complement components such as C1q and mannose-binding lectin (MBL) play an important role in the clearance of immune complexes. Anti-C1q antibodies are associated with lupus nephritis and reduced levels of the complement components. The objective of this study was to detect anti-C1q antibodies in SLE patients and to evaluate their association with the complement components. Sixty SLE patients were included, of whom 75% had lupus nephritis (LN) and 25% were without renal manifestations (non-LN). The disease activity was assessed at the time of evaluation by the systemic lupus erythematosus disease activity index (SLEDAI). Anti-C1q antibodies, circulating immune complexes, and serum MBL levels were detected by enzyme-linked immunosorbent assay. The anti-C1q antibody prevalence was 58.3%. The LN patients showed 60% anti-C1q positivity with a higher percentage in membranoproliferative glomerulonephritis patients (51.9%). Anti-dsDNA positivity was slightly higher among the anti-C1q positives than in the anti-C1q negatives (65.7% vs. 60%). A higher percentage of reduced C3 and C4 levels was noted among the anti-C1q positives. The LN patients showed a higher percentage of low MBL levels among anti-C1q negatives than in the anti-C1q positives (61.1% vs. 55.6%). Non-LN patients showed a higher percentage of low MBL levels among anti-C1q positives than among anti-C1q negatives (87.5% vs. 57.1%). Anti-C1q antibodies were found in both LN and non-LN patients, but there was no correlation with the clinical severity of the disease.

Animal models of systemic lupus erythematosus (SLE) and ex vivo assay design for drug discovery

Systemic Lupus Erythematosus (SLE) is a debilitating and often fatal autoimmune disease that involves multiple organ systems. It can develop for years before being diagnosed. Current treatments for SLE usually involve the use of cytotoxic or immunosuppressive agents that can lead to infection or cancer. The design of appropriate models and assays will determine the efficiency and speed with which an investigator can test a new chemical entity (NCE) or expect results to move a drug discovery program forward. This unit describes a series of preclinical assays for the identification of new agents for the treatment of SLE. Most importantly, this unit will guide the reader through a step-by-step process to select appropriate models, validation drugs, and readouts, depending on the objective of the study. The reader will acquire a working knowledge of what models are available and the potential advantages and disadvantages of each, including ex vivo assays relevant to the discovery of new SLE therapeutics.

Age-related differences in the clinical characteristics of systemic lupus erythematosus in children

The objective of this study was to determine how the clinical presentation of systemic lupus erythematosus in pediatric varied with the age of onset of the disease. We reviewed the charts of a total of 88 Chinese pediatric patients (pSLE) diagnosed and admitted first time to our hospitals between 2005 and 2008. Patients were divided into 3 groups, depending on the age at diagnosis: preschool (1-6 years), school age (7-11 years), and adolescent groups (12-18 years). Among the three groups, we compared the sex ratio, disease duration at diagnosis, symptoms at the onset of the disease, clinical manifestations, laboratory examinations, SLEDAI (Systemic Lupus Erythematosus Disease Activity Index) 2000, and SLICC/ACR SDI (Systemic Lupus International Collaborating Clinics/American College of Rheumatology Damage Index for Systemic Lupus Erythematosus). Most pediatric patients were in the adolescent group (47.7%), while the disease duration at diagnosis was shortest in preschool-age patients (0.65 ± 0.5 months). The most common symptoms at the onset of pSLE were fever, rash, arthritis, and seizures. Hematologic system and neuropsychiatric system were damaged commonly. The preschool-age patients had the shortest disease duration at diagnosis, the highest incidence of neuropsychiatric system involvement, and the poorest prognosis of all the age groups, especially the boys. Patients in adolescence had the peak incidence of pediatric SLE and high disease activity, begins to acquire some of the adult characteristics. School-age is a transition stage between other stages.

Deletion of Syk in neutrophils prevents immune complex arthritis

The K/BxN serum transfer model of arthritis is critically dependent on FcγR signaling events mediated by spleen tyrosine kinase (Syk). However, the specific cell types in which this signaling is required are not known. We report that deletion of Syk in neutrophils, achieved using syk(f/f) MRP8-cre(+) mice, blocks disease development in serum transfer arthritis. The syk(f/f) MRP8-cre(+) mice display absent joint disease and reduced deposition of pathogenic anti-glucose-6-phosphate isomerase Abs in the joint (with a reciprocal accumulation of these Abs in the peripheral circulation). Additionally, syk(f/f) MRP8-cre(+) mice manifest poor edema formation within 3 h after formation of cutaneous immune complexes (Arthus reaction). Together, this suggests that neutrophil-dependent recognition of immune complexes contributes significantly to changes in vascular permeability during the early phases of immune complex disease. Using mixed chimeric mice, containing both wild-type and syk(f/f) MRP8-cre(+) neutrophils, we find no impairment in recruitment of Syk-deficient neutrophils to the inflamed joint, but they fail to become primed, demonstrating lower cytokine production after removal from the joint. They also display an increased apoptotic rate compared with wild-type cells in the same joint. Mast cell-deficient c-kit(sh/sh) mice developed robust arthritis after serum transfer whereas c-kit(W/Wv) mice did not, suggesting that previous conclusions concerning the central role of mast cells in this model may need to be revised. Basophil-deficient mice also responded normally to K/BxN serum transfer. These results demonstrate that Syk-dependent signaling in neutrophils alone is critically required for arthritis development in the serum transfer model.

Depletion of autoreactive plasma cells and treatment of lupus nephritis in mice using CEP-33779, a novel, orally active, selective inhibitor of JAK2

Accumulating evidence suggests that autoreactive plasma cells play an important role in systemic lupus erythematosus (SLE). In addition, several proinflammatory cytokines promote autoreactive B cell maturation and autoantibody production. Hence, therapeutic targeting of such cytokine pathways using a selective JAK2 inhibitor, CEP-33779 (JAK2 enzyme IC(50) = 1.3 nM; JAK3 enzyme IC(50)/JAK2 enzyme IC(50) = 65-fold), was tested in two mouse models of SLE. Age-matched, MRL/lpr or BWF1 mice with established SLE or lupus nephritis, respectively, were treated orally with CEP-33779 at 30 mg/kg (MRL/lpr), 55 mg/kg or 100 mg/kg (MRL/lpr and BWF1). Studies included reference standard, dexamethasone (1.5 mg/kg; MRL/lpr), and cyclophosphamide (50 mg/kg; MRL/lpr and BWF1). Treatment with CEP-33779 extended survival and reduced splenomegaly/lymphomegaly. Several serum cytokines were significantly decreased upon treatment including IL-12, IL-17A, IFN-α, IL-1β, and TNF-α. Anti-nuclear Abs and frequencies of autoantigen-specific, Ab-secreting cells declined upon CEP-33779 treatment. Increased serum complement levels were associated with reduced renal JAK2 activity, histopathology, and spleen CD138(+) plasma cells. The selective JAK2 inhibitor CEP-33779 was able to mitigate several immune parameters associated with SLE advancement, including the protection and treatment of mice with lupus nephritis. These data support the possibility of using potent, orally active, small-molecule inhibitors of JAK2 to treat the debilitative disease SLE.

Evaluation of genetic association between an ITGAM non-synonymous SNP (rs1143679) and multiple autoimmune diseases

Many autoimmune diseases (ADs) share similar underlying pathology and have a tendency to cluster within families, supporting the involvement of shared susceptibility genes. To date, most of the genetic variants associated with systemic lupus erythematosus (SLE) susceptibility also show association with others ADs. ITGAM and its associated 'predisposing' variant (rs1143679, Arg77His), predicted to alter the tertiary structures of the ligand-binding domain of ITGAM, may play a key role for SLE pathogenesis. The aim of this study is to examine whether the ITGAM variant is also associated with other ADs. We evaluated case-control association between rs1143679 and ADs (N=18,457) including primary Sjögren's syndrome, systemic sclerosis, multiple sclerosis, rheumatoid arthritis, juvenile idiopathic arthritis, celiac disease, and type-1 diabetes. We also performed meta-analyses using our data in addition to available published data. Although the risk allele 'A' is relatively more frequent among cases for each disease, it was not significantly associated with any other ADs tested in this study. However, the meta-analysis for systemic sclerosis was associated with rs1143679 (p(meta)=0.008). In summary, this study explored the role of ITGAM in general autoimmunity in seven non-lupus ADs, and only found association for systemic sclerosis when our results were combined with published results. Thus ITGAM may not be a general autoimmunity gene but this variant may be specifically associated with SLE and systemic sclerosis.

Autoimmunity in 2010

There is now growing evidence that autoimmunity is the common trait connecting multiple clinical phenotypes albeit differences in tissue specificity, pathogenetic mechanisms, and therapeutic approaches cannot be overlooked. Over the past years we witnessed a constant growth of the number of publications related to autoimmune diseases in peer-reviewed journals of the immunology area. Original data referred to factors from common injury pathways (i.e. T helper 17 cells, serum autoantibodies, or vitamin D) and specific diseases such as multiple sclerosis, systemic lupus erythematosus, and rheumatoid arthritis. As an example, the issue of a latitudinal gradient in the prevalence and incidence rates has been proposed for all autoimmune diseases and was recently coined as geoepidemiology to suggest new environmental triggers for tolerance breakdown. The present article is aimed at reviewing the articles that were published over the past year in the major autoimmunity and immunology journals.

To B or not to B: role of B cells in pathogenesis of arthritis in HLA transgenic mice

Population studies have shown that amongst all the genetic factors linked with autoimmune disease development, MHC class II genes are the most significant. Experimental autoimmune arthritis resembling human rheumatoid arthritis (RA) can be induced in susceptible strains of mice following immunization with type II collagen (CIA). We generated transgenic mice lacking endogenous class II molecules and expressing various HLA genes including RA-associated, HLA-DRB1*0401 and HLA-DQ8, and RA-resistant, DRB1*0402, genes. The HLA molecules in these mice are expressed on the cell surface and can positively select CD4+ T cells expressing various Vβ T cell receptors. Endogenous class II invariant chain is required for proper functioning of the class II transgene. Arthritis development in transgenic mice is CD4+ and B cells dependent. Studies in humanized mice showed that B cells are required as antigen presenting cells in addition to antibody producing cells for the development of CIA. The transgenic mice expressing *0401 and *0401/DQ8 genes developed sex-biased arthritis with predominantly females being affected, similar to that of human RA. Further, the transgenic mice produced autoantibodies like rheumatoid factor and anti-cyclic antibodies. Antigen presentation by B cells leads to a sex-specific immune response in DRB1*0401 mice suggesting a role of B cells and HLA-DR in rendering susceptibility to develop arthritis in females.

A systemic lupus erythematosus-associated R77H substitution in the CD11b chain of the Mac-1 integrin compromises leukocyte adhesion and phagocytosis

The Mac-1 integrin is expressed mainly on myeloid cells and binds several ligands, including members of the ICAM family and the complement factor iC3b. It is involved in essential immunological processes, such as leukocyte extravasation and phagocytosis. In addition, Mac-1 has been described to negatively regulate immune cell signaling. Recently, a single nucleotide polymorphism conferring an amino acid change in the Mac-1 integrin extracellular domain, R77H, was shown to be associated with systemic lupus erythematosus. Here, we demonstrate that the R77H-substituted Mac-1 can be expressed on the cell surface in transfected cells and can undergo conformational changes in response to integrin activation. The affinity of the integrin for ICAMs is only partially reduced, but cell adhesion to ICAM-1 and ICAM-2 is severely compromised, and Jβ2.7 cells expressing R77H substituted integrins are deficient in adhesion to ICAM-1 under shear flow conditions. Importantly, cell adhesion to the complement factor iC3b is also diminished, and COS cells expressing R77H-substituted integrins display reduced iC3b-dependent phagocytosis. In addition, U937 cells expressing R77H-CD11b display increased IL-6 production as compared with WT-CD11b-expressing cells. These results suggest that the R77H substitution results in the deficiency of the mutated integrin to mediate cell adhesion to ligands such as ICAMs and iC3b. These deficiencies may ultimately lead to detrimental effects on the immune system and contribute to the development of systemic lupus erythematosus.