DR3 and nonDR3 associated complement component C4A deficiency in systemic lupus erythematosus

TScan-II: A genome-scale platform for the de novo identification of CD4+ T cell epitopes

CD4+ T cells play fundamental roles in orchestrating immune responses and tissue homeostasis. However, our inability to associate peptide human leukocyte antigen class-II (HLA-II) complexes with their cognate T cell receptors (TCRs) in an unbiased manner has hampered our understanding of CD4+ T cell function and role in pathologies. Here, we introduce TScan-II, a highly sensitive genome-scale CD4+ antigen discovery platform. This platform seamlessly integrates the endogenous HLA-II antigen-processing machinery in synthetic antigen-presenting cells and TCR signaling in T cells, enabling the simultaneous screening of multiple HLAs and TCRs. Leveraging genome-scale human, virome, and epitope mutagenesis libraries, TScan-II facilitates de novo antigen discovery and deep exploration of TCR specificity. We demonstrate TScan-II's potential for basic and translational research by identifying a non-canonical antigen for a cancer-reactive CD4+ T cell clone. Additionally, we identified two antigens for clonally expanded CD4+ T cells in Sjögren's disease, which bind distinct HLAs and are expressed in HLA-II-positive ductal cells within affected salivary glands.

A Major B Cell Epitope Present on the Apoptotic but Not the Intact Form of the U1-70-kDa Ribonucleoprotein Autoantigen

Apoptotically modified forms of autoantigens have been hypothesized to participate in lupus immunopathogenesis. This study identifies a major B cell epitope present on the apoptotic but not the intact form of the U1-70-kDa ribonucleoprotein lupus autoantigen (70k). Human autoimmune sera with strong recognition of apoptotic 70k and minimal recognition of intact 70k were identified and tested for reactivity to truncated forms of 70k by immunoblot and ELISA. Patient sera that preferentially recognized apoptotic 70k were specific for an epitope dependent on residues 180-205 of the protein. This epitope was also recognized by 19 of 28 (68%) intact anti-70k-positive autoimmune human sera with Abs also recognizing apoptotic but not the intact form 70k, but only 1 of 9 (11%) intact 70k-positive sera without such Abs (Fisher's exact, p = 0.0055). Immunization of HLA-DR4-transgenic C57BL/6 mice with a peptide containing this epitope induced anti-70k immunity in 13 of 15 mice, including Abs recognizing apoptotic but not intact forms of autoantigens in 12 of 15 mice. Anti-70k responder mice also developed spreading of immunity to epitopes on the endogenous form of 70k, and proliferative lung lesions consistent with those described in patients with anti-70k autoimmunity. Thus, a major epitope in the B cell response to U1-70 kDa localizes to the RNA binding domain of the molecule, overlaps with the most common T cell epitope in the anti-70k response, and is not present on the intact form of the 70k molecule. Immunization of mice against this epitope induces an immune response with features seen in human anti-70k autoimmune disease.

T cell immunity in connective tissue disease patients targets the RNA binding domain of the U1-70kDa small nuclear ribonucleoprotein

Although the T cell dependence of autoimmune responses in connective tissue diseases has been well established, limited information exists regarding the T cell targeting of self Ags in humans. To characterize the T cell response to a connective tissue disease-associated autoantigen, this study generated T cell clones from patients using a set of peptides encompassing the entire linear sequence of the 70-kDa subunit of U1 snRNP (U1-70kDa) small nuclear ribonucleoprotein. Despite the ability of U1-70kDa to undergo multiple forms of Ag modification that have been correlated with distinct clinical disease phenotypes, a remarkably limited and consistent pattern of T cell targeting of U1-70kDa was observed. All tested T cell clones generated against U1-70kDa were specific for epitopes within the RNA binding domain (RBD) of the protein. High avidity binding of the RBD with U1-RNA was preserved with the disease-associated modified forms of U1-70kDa tested. The high avidity interaction between the U1-RBD on the polypeptide and U1-RNA may be critical in immune targeting of this region in autoimmunity. The T cell autoimmune response to U1-70kDa appears to have less diversity than is seen in the humoral response; and therefore, may be a favorable target for therapeutic intervention.

Long PCR detection of the C4A null allele in B8-C4AQ0-C4B1-DR3

The genes coding for the two components of complement 4 (C4), C4A and C4B, are located within the major histocompatibility complex (MHC) on the short arm of chromosome 6. Several studies have shown that deficiency of C4A is associated with systemic lupus erythematosus (SLE), rheumatoid arthritis and scleroderma. A large deletion covering most of the C4A gene and the 21-hydroxylase-A (21-OHA) pseudogene found on the extended haplotype B8-C4AQ0-C4B1-DR3 is estimated to account for approximately two-thirds of C4A deficiency in Caucasian SLE patients. Detection of this C4A null allele has been technically difficult due to the high degree of homology between C4A and C4B, with protein analysis and restriction fragment length polymorphism (RFLP) analysis using Southern blotting being the only approaches available. In this study, a long PCR strategy was used to rapidly genotype for the C4A deletion through specific primer design. The methodology makes use of the unique sequence of the G11 gene upstream of C4A and the sequence of a 6.4 kb retrotransposon, the human endogenous retrovirus HERV-K(C4), which is present in intron 9 of C4A but absent in the case of the deletion.

The genetics of rheumatoid arthritis: influences on susceptibility, severity, and treatment response

There has been an explosion of knowledge of genetic variations among different populations and the influence of genetics on complex diseases such as rheumatoid arthritis (RA). Although class II major histocompatibility complex (MHC) alleles are important contributors, there are likely multiple other genes that modulate the disease phenotype. Genetic markers may allow prediction of response to particular treatments. Given the recent approval of tumor necrosis factors (TNF) inhibitors and the large number of biologic agents currently undergoing clinical trials, pharmacogenetic markers may prove to be clinically useful.

A study of the association of HLA DR, DQ, and complement C4 alleles with systemic lupus erythematosus in Iceland

OBJECTIVE

To perform an exploratory analysis of the relative contribution of single MHC genes to the pathogenesis of systemic lupus erythematosus (SLE) in a homogenous white population.

METHODS

MHC class II alleles and C4 allotypes were determined in 64 SLE patients and in ethnically matched controls. HLA-DR and DQ typing was performed by polymerase chain reaction amplification with sequence specific primers. C4 allotypes were determined by agarose gel electrophoresis.

RESULTS

The frequency of C4A*Q0 was significantly higher in patients than in controls (46.9% v 25.3%, p = 0.002). HLA-DRB1, DQA1, and DQB1 alleles in the whole group of SLE patients were not significantly different from those of controls. On the other hand increase in DRB1*03 was observed in the group of patients with C4A*Q0, as compared with patients with other C4A allotypes (p = 0.047). There was no significant correlation between severe and mild disease, as judged by the SLEDAI, and HLADR, DQ alleles and comparing the patients with C4A*Q0 with those with other C4A allotypes there was no significant difference regarding clinical manifestations.

CONCLUSION

The results are consistent with the argument that C4A deficiency contributes independently to susceptibility and the pathogenesis of SLE. C4A*Q0 in SLE patients in Iceland shows weaker linkage disequilibrium with DR3 genes than reported in most other white populations and emphasises the role of ethnicity.

Clinical correlates, serum autoantibodies and the role of the major histocompatibility complex in French Canadian and non-French Canadian Caucasians with SLE

OBJECTIVE

To investigate the predisposing role of major histocompatibility complex (MHC) genes to autoantibody production and clinical manifestations comparing French Canadian and Non-French Canadian Caucasians with systemic lupus erythematosus (SLE) METHODS: Ninety-one Caucasian patients with SLE were studied. Clinical manifestations, autoantibody expression and HLA-A, B, (serology), DR, DQ and C4A gene deletion (restriction fragment length polymorphism [RFLP] typing) were determined.

RESULTS

Photosensitivity was present in all SLE subjects with anti-Ro antibodies (P=0.001, RR=13.1, CI=1.8, 564). Photosensitivity was further associated with the HLA-A1, C4A gene deletion haplotype. More strikingly, C4A gene deletion was associated with anti-Ro (P=0.008, RR=4.6, CI=1.4, 16.2) and anti-La (P=0.02, RR=11.7, CI=1.4, 549) autoantibodies. This relationship was also significant for anti-Ro antibody in the French Canadian patients (P=0.01, RR=21.3, CI=1.7, 105.3). In contrast, anti-dsDNA autoantibodies were negatively associated with photosensitivity (P=0.02, RR=0.3, CI=0.07, 0.8) and correlated with HLA-DR15 (P=0.006, RR=4.2, CI=1.5, 12.8) and Dw2 (P=0.009, RR=3.9, CI=1.4, 11.9).

CONCLUSION

C4A gene deletion has a previously unrecognized powerful association with anti-Ro and anti-La autoantibodies. These results support the concept of divergent MHC gene associations with autoantibody expression and emphasize the influence of ethnicity on the immunogenetic study of SLE.

Molecular heterogeneity in deficiency of complement protein C2 type I

Deficiency of the complement protein C2 (C2D), one of the most common genetic deficiencies of the complement system, is associated with rheumatological disorders and increased susceptibility to infection. Two types of C2D have been recognized, each in the context of specific major histocompatibility complex (MHC) haplotypes; type I, a deletion, frameshift and premature stop codon resulting in absence of detectable C2 protein synthesis, and type II, missense mutations resulting in a block in secretion of C2 proteins. Analysis of C2 expression in a child with C2 deficiency, a MHC haplotype different from those associated with type I or II C2D, and recurrent infections revealed additional molecular heterogeneity among C2 deficient patients. No detectable C2 protein was synthesized in the child's fibroblasts under conditions supporting C2 synthesis and secretion in normals and the child's C2 mRNA was reduced to 42% of normal. Nucleotide sequencing of RT-PCR fibroblast mRNA and genomic DNA revealed a type I C2 deficiency (28 base-pair deletion) on one allele and a previously unrecognized two base-pair deletion in exon 2 on the other. Expression of the closely linked factor B gene was markedly decreased (Bf mRNA 25% of normal), though Bf was up-regulated appropriately by interferon-gamma and the flanking sequence containing the Bf promoter was normal in this C2-deficient patient. Moreover, the concentration of Bf protein was normal in the patient's plasma.

Combined heterozygous deficiency of the classical complement pathway proteins C2 and C4

Genetic deficiencies of components of the classical pathway of complement activation are associated with an increased risk for the development of autoimmune and immune complex-mediated diseases. In the present study we report on the molecular and clinical features associated with combined heterozygous C4 and C2 deficiency in 15 individuals investigated within six families. Approximately 30% of the individuals manifested SLE or another autoimmune condition. Heterozygous C2 deficiency was related to a 28-bp deletion in the C2 gene (C2 deficiency type I), in most cases within the HLA-A25 B18 C2Q0 BfS C4A4B2 DR2 haplotype. Among 13 partial C4-deficient haplotypes transmitted, 8 carried C4A*Q0 alleles and 5 C4B*Q0 alleles. In seven cases the C4A*Q0 alleles were associated with a deletion of the C4A/CYP21P genes within the HLA-B8 C2C BfS C4AQ0B1 DR3 haplotype. In three cases, the C4B*Q0 allele was associated with a deletion of the C4B/CYP21P genes within the HLA-B18 C2C BfF1 C4A3BQ0 DR3 haplotype. In the other cases, C4A*Q0 or C4B*Q0 was dependent on as yet uncharacterized defects in the C4 gene or in C4 gene expression. In view of the relatively high frequency of heterozygous C4 deficiency in the normal Caucasian population, the expected frequency of the combined deficiency should approximate 0.001.

Systemic lupus erythematosus

Systemic Lupus Erythematosus (SLE) of childhood is a complex and challenging disease which can occur at any age. Identification of disease early in it's course and aggressive, appropriate management leads to improved outcome for an individual child. The history of SLE indicates how much progress has been made in the last quarter century. A discussion of the etiopathogenesis of SLE demonstrates the complexity of the syndrome. This is followed by a description of clinical manifestations, including diagnostic criteria, differential diagnosis and suggested methods for eliciting important symptoms to make the diagnosis. Evaluation of specific organs is next reviewed highlighting critical organ manifestations that are significant for future prognosis. Treatment of SLE includes a variety of medications, including non-steroidal anti-inflammatory medications, steroids and immuno-suppressive drugs. Attention to physical activity, stress and nutrition is equally important. Signs and symptoms that indicate disease flare or infection are described. Lastly, related syndromes are reviewed.

Genetic deficiencies of complement

Genetic deficiencies of proteins of the complement system are associated with diverse clinical phenotypes. These clinical manifestations vary as a function of the specific component that is missing. Molecular and cellular biological methods, coupled with more intensive clinical studies, have defined the pathophysiological basis for this set of genetic disorders. Insights into the normal function of complement and its role in immunopathology have been derived from the extensive work in this field during the past few years.

Mannose-binding protein gene polymorphism in systemic lupus erythematosus

OBJECTIVE

To determine whether an allelic form of mannose-binding protein (MBP) incapable of activating complement is associated with susceptibility to systemic lupus erythematosus (SLE).

METHODS

MBP allele frequencies were determined by amplification refractory mutation system-polymerase chain reaction in 102 white SLE patients and 136 controls.

RESULTS

The MBP allele that is unable to activate complement was present in 42 SLE patients (41%) and in 41 controls (30%) (P = 0.08, odds ratio [OR] = 1.6, 95% confidence interval [95% CI] 1.0-2.8). The gene frequency of this allele was 0.25 in SLE patients and 0.19 in controls (P = 0.08, OR = 1.5, 95% CI 1.0-2.3).

CONCLUSION

Our results suggest that this allele of the MBP gene represents a minor risk factor for SLE.

Comparative studies of the major histocompatibility complex in French Canadian and non-French Canadian Caucasians with systemic lupus erythematosus

OBJECTIVE

To investigate and compare the predisposing role of major histocompatibility complex (MHC) genes in systemic lupus erythematosus (SLE) in French Canadian and non-French Canadian (mainly Anglo-Saxon descent) Caucasian subjects.

METHODS

HLA-A, B, C (serology), DR, and DQ (restriction fragment length polymorphism [RFLP] typing) were determined. RFLP defining a large C4A,21-OHA deletion (Taq I C4) and an Nco I tumor necrosis factor alpha (TNF alpha) RFLP were analyzed in 91 Caucasian Canadians and 91 ethnically matched control subjects.

RESULTS

In the total SLE and non-French Canadian SLE populations, HLA-B8, DR3(DR17), Dw24, DQ2, and the C4A gene deletion were associated with SLE. These HLA specificities and the C4A gene deletion were not significantly increased in French Canadian SLE patients compared with ethnically matched controls. When present in French Canadians, the C4A gene deletion was less closely associated with HLA-DR3(DR17), Dw24, DQ2 than in other Caucasians. HLA-DQ6 was associated with SLE in French Canadians. No association of the 2-allele Nco I TNF alpha RFLP with SLE was found in this population, in either ethnic group.

CONCLUSION

These results support the importance of ethnic background in the study of MHC genes and SLE. The extended HLA-B8,DR3,C4A null haplotype is found mainly in SLE patients of Anglo-Saxon descent, while the DQ6 specificity is associated with SLE in French Canadians. This relatively genetically homogeneous Caucasian population offers the opportunity to study non-HLA-B8,DR3-linked MHC influence in SLE.

The clinical genetics of lupus

Genetic aspects of lupus are reviewed, including recognition of genetic and clinical heterogeneity, genetic factors in the aetiology and heritability of disease, reproductive implications and genetic counselling of patients. Despite a large literature on the genetic epidemiology and immunogenetics of lupus, it remains difficult to apply the results of laboratory findings to the circumstances of individual patients. Generally, lupus is not transmitted as a simple Mendelian trait, and genetic counselling is based on the multifactorial model of disease aetiology with interaction of multiple genetic and environmental factors. Further studies are needed to clarify the heritability of lupus and improve the data for recurrence risk prediction in lupus families.

Systemic lupus erythematosus

Systemic lupus erythematosus is a prototypic autoimmune disease characterized by antinuclear antibody production. In recent investigations, the contributions of various polymorphic immune response gene systems to disease pathogenesis have been analyzed. Unique cellular and molecular studies have also established the role of 'autoantigen drive' in autoantibody induction and its relationship to polyclonal B-cell activation.

Immunoglobulin heavy chain constant-region gene polymorphism in systemic lupus erythematosus

Systemic lupus erythematosus (SLE) is associated with immunoglobulin allotypes in several ethnic groups. In this study, we investigated the association of a Bst EII immunoglobulin heavy chain constant-region gene restriction fragment length polymorphism with SLE in patients from the US and Mexico. A 3-kb restriction fragment was observed with significantly decreased frequency in randomly selected Mexican SLE patients and in Mexican SLE patients in multiplex families. However, no such association was observed in SLE patients from the US. Thus, the absence of a 3.0-kb Bst EII restriction fragment from immunoglobulin heavy chain constant-region genes provides a marker for SLE in Mexican individuals.