Baricitinib-associated changes in global gene expression during a 24-week phase II clinical systemic lupus erythematosus trial implicates a mechanism of action through multiple immune-related pathways

OBJECTIVE

To characterise the molecular pathways impacted by the pharmacologic effects of the Janus kinase (JAK) 1 and JAK2 inhibitor baricitinib in SLE.

METHODS

In a phase II, 24-week, randomised, placebo-controlled, double-blind study (JAHH), RNA was isolated from whole blood in 274 patients and analysed using Affymetrix HTA2.0 array. Serum cytokines were measured using ultrasensitive quantitative assays.

RESULTS

Gene expression profiling demonstrated an elevation of STAT1, STAT2 and multiple interferon (IFN) responsive genes at baseline in patients with SLE. Statistical and gene network analyses demonstrated that baricitinib treatment reduced the mRNA expression of functionally interconnected genes involved in SLE including STAT1-target, STAT2-target and STAT4-target genes and multiple IFN responsive genes. At baseline, serum cytokines IFN-α, IFN-γ, interleukin (IL)-12p40 and IL-6 were measurable and elevated above healthy controls. Treatment with baricitinib significantly decreased serum IL-12p40 and IL-6 cytokine levels at week 12, which persisted through week 24.

CONCLUSION

Baricitinib treatment induced significant reduction in the RNA expression of a network of genes associated with the JAK/STAT pathway, cytokine signalling and SLE pathogenesis. Baricitinib consistently reduced serum levels of two key cytokines implicated in SLE pathogenesis, IL-12p40 and IL-6.

Baricitinib for systemic lupus erythematosus: a double-blind, randomised, placebo-controlled, phase 2 trial

BACKGROUND

Patients with systemic lupus erythematosus have substantial unmet medical need. Baricitinib is an oral selective Janus kinase (JAK)1 and JAK2 inhibitor that we hypothesised might have therapeutic benefit in patients with systemic lupus erythematosus.

METHODS

In this double-blind, multicentre, randomised, placebo-controlled, 24-week phase 2 study, patients were recruited from 78 centres in 11 countries. Eligible patients were aged 18 years or older, had a diagnosis of systemic lupus erythematosus, and had active disease involving skin or joints. We randomly assigned patients (1:1:1) to receive once-daily baricitinib 2 mg, baricitinib 4 mg, or placebo for 24 weeks. The primary endpoint was the proportion of patients achieving resolution of arthritis or rash at week 24, as defined by Systemic Lupus Erythematosus Disease Activity Index-2000 (SLEDAI-2K). Efficacy and safety analyses included all patients who received at least one dose of study drug. This study is registered with ClinicalTrials.gov, number NCT02708095.

FINDINGS

Between March 24, 2016, and April 27, 2017, 314 patients were randomly assigned to receive placebo (n=105), baricitinib 2 mg (n=105), or baricitinib 4 mg (n=104). At week 24, resolution of SLEDAI-2K arthritis or rash was achieved by 70 (67%) of 104 patients receiving baricitinib 4 mg (odds ratio [OR] vs placebo 1·8, 95% CI 1·0-3·3; p=0·0414) and 61 (58%) of 105 patients receiving baricitinib 2 mg (OR 1·3, 0·7-2·3; p=0·39). Adverse events were reported in 68 (65%) patients in the placebo group, 75 (71%) patients in the baricitinib 2 mg group, and 76 (73%) patients in the baricitinib 4 mg group. Serious adverse events were reported in ten (10%) patients receiving baricitinib 4 mg, 11 (10%) receiving baricitinib 2 mg, and five (5%) receiving placebo; no deaths were reported. Serious infections were reported in six (6%) patients with baricitinib 4 mg, two (2%) with baricitinib 2 mg, and one (1%) with placebo.

INTERPRETATION

The baricitinib 4 mg dose, but not the 2 mg dose, significantly improved the signs and symptoms of active systemic lupus erythematosus in patients who were not adequately controlled despite standard of care therapy, with a safety profile consistent with previous studies of baricitinib. This study provides the foundation for future phase 3 trials of JAK1/2 inhibition with baricitinib as a new potential oral therapy for systemic lupus erythematosus.

FUNDING

Eli Lilly and Company.

Gene Expression and Pharmacodynamic Changes in 1,760 Systemic Lupus Erythematosus Patients From Two Phase III Trials of BAFF Blockade With Tabalumab

Objective

To characterize baseline gene expression and pharmacodynamically induced changes in whole blood gene expression in 1,760 systemic lupus erythematosus (SLE) patients from 2 phase III, 52‐week, randomized, placebo‐controlled, double‐blind studies in which patients were treated with the BAFF‐blocking IgG4 monoclonal antibody tabalumab.

Methods

Patient samples were obtained from SLE patients from the ILLUMINATE‐1 and ILLUMINATE‐2 studies, and control samples were obtained from healthy donors. Blood was collected in Tempus tubes at baseline, week 16, and week 52. RNA was analyzed using Affymetrix Human Transcriptome Array 2.0 and NanoString.

Results

At baseline, expression of the interferon (IFN) response gene was elevated in patients compared with controls, with 75% of patients being positive for this IFN response gene signature. There was, however, substantial heterogeneity of IFN response gene expression and complex relationships among gene networks. The IFN response gene signature was a predictor of time to disease flare, independent of anti–double‐stranded DNA (anti‐dsDNA) antibody and C3 and C4 levels, and overall disease activity. Pharmacodynamically induced changes in gene expression following tabalumab treatment were extensive, occurring predominantly in B cell–related and immunoglobulin genes, and were consistent with other pharmacodynamic changes including anti‐dsDNA antibody, C3, and immunoglobulin levels.

Conclusion

SLE patients demonstrated increased expression of an IFN response gene signature (75% of patients had an elevated IFN response gene signature) at baseline in ILLUMINATE‐1 and ILLUMINATE‐2. Substantial heterogeneity of gene expression was detected among individual patients and in gene networks. The IFN response gene signature was an independent risk factor for future disease flares. Pharmacodynamic changes in gene expression were consistent with the mechanism of BAFF blockade by tabalumab.

Diagnosis and risk stratification in patients with anti-RNP autoimmunity

INTRODUCTION

Anti-RNP autoantibodies occur either in mixed connective tissue disease (MCTD) (with a frequently favorable prognosis), or in systemic lupus erythematosus (SLE) cases with aggressive major organ disease. It is uncertain how to assess for the risk of severe disease in anti-RNP + patients.

METHODS

Following institutional review board-approved protocols, clinical data and blood were collected from patients with known or suspected anti-RNP autoimmunity and normal controls in a cohort study. Samples were screened for parameters of immune activation. Groups were compared based on clinical diagnoses, disease classification criteria, disease activity and specific end-organ clinical manifestations.

RESULTS

Ninety-seven per cent of patients satisfying Alarcon-Segovia MCTD criteria also met Systemic Lupus International Collaborating Clinic (SLICC) SLE criteria, while 47% of the anti-RNP + SLE patients also met MCTD criteria. Among SLICC SLE patients, MCTD criteria were associated with reduced rates of renal disease (odds ratio (OR) 4.3, 95% confidence interval (CI) 1.3-14.0), increased rates of Raynaud's phenomenon (OR 3.5, 95% CI 1.3-9.5) and increased serum B-cell maturation antigen, transmembrane activator and CAML interactor and TNFα levels. Circulating immune markers and markers of type I interferon activation were not effective at distinguishing clinical subgroups.

CONCLUSIONS

Among anti-RNP patients, the question of MCTD versus SLE is not either/or: most MCTD patients also have lupus. MCTD classification criteria (but not a broad set of immune markers) distinguish a subset of SLE patients at reduced risk for renal disease.

Seed train development for the fermentation of bagasse from sweet sorghum and sugarcane using a simplified fermentation process

A process was developed for seed culture expansion (3.6 million-fold) using 5% of the hemicellulose hydrolysate from dilute acid pretreatment as the sole organic nutrient and source of sugar. Hydrolysate used for seed growth was neutralized with ammonia and combined with 1.0mM sodium metabisulfite immediately before inoculation. This seed protocol was tested with phosphoric acid pretreated sugarcane and sweet sorghum bagasse using a simplified process with co-fermentation of fiber, pentoses, and hexoses in a single vessel (SScF). A 6h liquefaction (L) step improved mixing prior to inoculation. Fermentations (L+SScF process) were completed in 72 h with high yields (>80 gal/US ton). Ethanol titers for this L+SScF process ranged from 24 g/L to 32 g/L, and were limited by the bagasse concentration (10% dry matter).

IL-17A is essential for cell activation and inflammatory gene circuits in subjects with psoriasis

BACKGROUND

In subjects with psoriasis, inflammation and epidermal hyperplasia are thought to be controlled by T cell-derived cytokines. Evidence suggests that the T(H)17 cell cytokine IL-17A (IL-17) might play a role in disease pathogenesis.

OBJECTIVE

We sought to understand the effect that neutralization of IL-17 has on the clinical features of psoriasis and to understand the role that IL-17 has in inflammatory pathways underlying psoriasis in human subjects.

METHODS

We examined skin lesions obtained from 40 subjects participating in a phase I, randomized, double-blind, placebo-controlled trial of the anti-IL-17 mAb ixekizumab (previously LY2439821) in which subjects received 5, 15, 50, or 150 mg of subcutaneous ixekizumab or placebo at weeks 0, 2, and 4.

RESULTS

There were significant dose-dependent reductions from baseline in keratinocyte proliferation, hyperplasia, epidermal thickness, infiltration into the dermis and epidermis by T cells and dendritic cells, and keratinocyte expression of innate defense peptides at 2 weeks. By week 6, the skin appeared normal. Quantitative RT-PCR and microarrays revealed an ablation of the disease-defining mRNA expression profile by 2 weeks after the first dose of study drug. The effect of IL-17 blockade on expression of genes synergistically regulated by IL-17 and TNF-α was of higher magnitude at 2 weeks than in prior studies with TNF-α antagonism.

CONCLUSION

Our data suggest that IL-17 is a key "driver" cytokine that activates pathogenic inflammation in subjects with psoriasis. Neutralizing IL-17 with ixekizumab might be a successful therapeutic strategy in psoriasis.

IL-17A is essential for cell activation and inflammatory gene circuits in subjects with psoriasis

BACKGROUND

In subjects with psoriasis, inflammation and epidermal hyperplasia are thought to be controlled by T cell-derived cytokines. Evidence suggests that the T(H)17 cell cytokine IL-17A (IL-17) might play a role in disease pathogenesis.

OBJECTIVE

We sought to understand the effect that neutralization of IL-17 has on the clinical features of psoriasis and to understand the role that IL-17 has in inflammatory pathways underlying psoriasis in human subjects.

METHODS

We examined skin lesions obtained from 40 subjects participating in a phase I, randomized, double-blind, placebo-controlled trial of the anti-IL-17 mAb ixekizumab (previously LY2439821) in which subjects received 5, 15, 50, or 150 mg of subcutaneous ixekizumab or placebo at weeks 0, 2, and 4.

RESULTS

There were significant dose-dependent reductions from baseline in keratinocyte proliferation, hyperplasia, epidermal thickness, infiltration into the dermis and epidermis by T cells and dendritic cells, and keratinocyte expression of innate defense peptides at 2 weeks. By week 6, the skin appeared normal. Quantitative RT-PCR and microarrays revealed an ablation of the disease-defining mRNA expression profile by 2 weeks after the first dose of study drug. The effect of IL-17 blockade on expression of genes synergistically regulated by IL-17 and TNF-α was of higher magnitude at 2 weeks than in prior studies with TNF-α antagonism.

CONCLUSION

Our data suggest that IL-17 is a key "driver" cytokine that activates pathogenic inflammation in subjects with psoriasis. Neutralizing IL-17 with ixekizumab might be a successful therapeutic strategy in psoriasis.

An external validation study of a classification of mixed connective tissue disease and systemic lupus erythematosus patients

Mixed Connective Tissue Disease (MCTD) and Systemic Lupus Erythematosus (SLE) are autoimmune rheumatic diseases that are difficult for physicians to diagnose and to distinguish for a variety of reasons. The correct classification of these two diseases is a crucial issue for clinicians who treat autoimmune rheumatic diseases. In prior research, medical risk factors represented by instrument or laboratory measures and physician judgments (12 key features for MCTD and 12 key features for SLE) were parameterized with a one parameter logistic function in a Rasch model. Those results identified separate diagnostic dimensions for MCTD and SLE. This procedure was replicated in the present research with a sample of largely African American and Hispanic patients. Results verified separate dimensions for MCTD and SLE, which suggests MCTD is a separate disease from SLE.

Injection of air into the headspace improves fermentation of phosphoric acid pretreated sugarcane bagasse by Escherichia coli MM170

Microaeration (injecting air into the headspace) improved the fermentation of hemicellulose hydrolysates obtained from the phosphoric acid pretreatment of sugarcane bagasse at 170°C for 10 min. In addition, with 10% slurries of phosphoric acid pretreated bagasse (180°C, 10 min), air injection into the headspace promoted xylose utilization and increased ethanol yields from 0.16 to 0.20 g ethanol/g bagasse dry weight using a liquefaction plus simultaneous saccharification and co-fermentation process (L+SScF). This process was scaled up to 80 L using slurries of acid pretreated bagasse (96 h incubation; 0.6L of air/min into the headspace) with ethanol yields of 312-347 L (82-92 gal) per tone (dry matter), corresponding to 0.25 and 0.27 g/g bagasse (dry weight). Injection of small amounts of air into the headspace may provide a convenient alternative to subsurface sparging that avoids problems of foaming, sparger hygiene, flotation of particulates, and phase separation.

Effect of reduced sulfur compounds on the fermentation of phosphoric acid pretreated sugarcane bagasse by ethanologenic Escherichia coli

The addition of reduced sulfur compounds (thiosulfate, cysteine, sodium hydrosulfite, and sodium metabisulfite) increased growth and fermentation of dilute acid hydrolysate of sugarcane bagasse by ethanologenic Escherichia coli (strains LY180, EMFR9, and MM160). With sodium metabisulfite (0.5mM), toxicity was sufficiently reduced that slurries of pretreated biomass (10% dry weight including fiber and solubles) could be fermented by E. coli strain MM160 without solid-liquid separation or cleanup of sugars. A 6-h liquefaction step was added to improve mixing. Sodium metabisulfite also caused spectral changes at wavelengths corresponding to furfural and soluble products from lignin. Glucose and cellobiose were rapidly metabolized. Xylose utilization was improved by sodium metabisulfite but remained incomplete after 144 h. The overall ethanol yield for this liquefaction plus simultaneous saccharification and co-fermentation process was 0.20 g ethanol/g bagasse dry weight, 250 L/tonne (61 gal/US ton).

Simplified process for ethanol production from sugarcane bagasse using hydrolysate-resistant Escherichia coli strain MM160

Hexose and pentose sugars from phosphoric acid pretreated sugarcane bagasse were co-fermented to ethanol in a single vessel (SScF), eliminating process steps for solid-liquid separation and sugar cleanup. An initial liquefaction step (L) with cellulase was included to improve mixing and saccharification (L+SScF), analogous to a corn ethanol process. Fermentation was enabled by the development of a hydrolysate-resistant mutant of Escherichia coli LY180, designated MM160. Strain MM160 was more resistant than the parent to inhibitors (furfural, 5-hydroxymethylfurfural, and acetate) formed during pretreatment. Bagasse slurries containing 10% and 14% dry weight (fiber plus solubles) were tested using pretreatment temperatures of 160-190°C (1% phosphoric acid, 10 min). Enzymatic saccharification and inhibitor production both increased with pretreatment temperature. The highest titer (30 g/L ethanol) and yield (0.21 g ethanol/g bagasse dry weight) were obtained after incubation for 122 h using 14% dry weight slurries of pretreated bagasse (180°C).

T cell vaccination therapy in an induced model of anti-RNP autoimmune glomerulonephritis

To establish the relevance of targeting disease-associated T cells in anti-RNP-associated glomerulonephritis, mice developing nephritis following immunization with U1-70-kd small nuclear ribonucleoprotein (snRNP) were treated with a single dose of irradiated antigen-selected T cell vaccine. T cell receptor usage in nephritic kidneys revealed oligoclonal use of T Cell Receptor V Beta (TRBV) genes as previously found in spleens and lungs of immunized mice with pulmonary disease. The CDR3 regions from T cell isolates showed sequence homology to those in humans with anti-RNP autoimmunity. Following T cell vaccination, urinalysis returned to normal in 5/7 treated mice (71% response rate) whereas all mock-treated mice continued to have an active urinary sediment (Fisher's Exact p=0.02). An oligoclonal population of T cells homologous to those identified in humans with anti-RNP autoimmunity is implicated in disease pathogenesis, and T cell vaccination is associated with a high rate of clinical improvement in established nephritis.

Anti-ribonucleoprotein antibodies mediate enhanced lung injury following mesenteric ischemia/reperfusion inRag-1−/−mice

Natural Abs and autoantibodies bind antigens displayed by ischemia-conditioned tissues, followed by complement activation and enhanced tissue injury during reperfusion. Anti-ribonucleoprotein (RNP) Ab is associated with lung disease in patients with autoimmune disease but it is not known whether these abs contribute to lung injury. Mesenteric I/R in mice leads to local and remote lung injury. Accordingly, we used this model to investigate whether anti-RNP Abs would reconstitute I/R damage with prominent lung damage in injury-resistant Rag1(-/-) animals. Rag1(-/-) mice injected with anti-RNP Ab containing serum and subjected to mesenteric I/R suffered greater intestinal injury than control-treated and sham-operated animals. The magnitude of the reconstituted damage was anti-RNP Ab titer-dependent. Anti-RNP Ab-treated animals demonstrated a dose-dependent increase in lung histologic injury scores compared to control and sham animals. Anti-RNP mediated injury was shown to be complement dependent. These experiments reveal a novel mechanism whereby anti-RNP Abs contributes to the development of pulmonary pathology in patients with autoimmune diseases following exposure of remote organs to I/R injury.

Tissue targeting of anti-RNP autoimmunity: effects of T cells and myeloid dendritic cells in a murine model

OBJECTIVE

To explore the role of immune cells in anti-RNP autoimmunity in a murine model of pneumonitis or glomerulonephritis, using adoptive transfer techniques.

METHODS

Donor mice were immunized with 50 mug of U1-70-kd small nuclear RNP fusion protein and 50 mug of U1 RNA adjuvant. Whole splenocytes as well as CD4+ cell and dendritic cell (DC) subsets from the immunized mice were infused into naive syngeneic recipients. Anti-RNP and T cell responses were assessed by immunoblotting, enzyme-linked immunosorbent assay, and flow cytometry. Development of renal or lung disease was assessed by histology and urinalysis.

RESULTS

Unfractionated splenocytes from donor mice without proteinuria induced predominantly lung disease in recipients (8 [57%] of 14 versus 2 [14%] of 14 developing renal disease; P = 0.046). However, infusion of CD4+ cells from donors without proteinuria induced renal disease more frequently than lung disease (7 [70%] of 10 versus 2 [20%] of 10; P = 0.01); adoptive transfer of RNP+CD4+ T cells from short-term culture yielded similar results (renal disease in 8 [73%] of 11 recipients versus lung disease in 3 [27%] of 11). Cotransfer of splenic myeloid DCs and CD4+ T cells from immunized donors prevented induction of renal disease in all 5 recipients (P = 0.026 versus recipients of fresh CD4+ cells alone), although lung disease was still observed in 1 of 5 mice. Transfer of myeloid DCs alone from immunized donors induced lung disease in 3 (60%) of 5 recipients, without evidence of nephritis. Cotransfer of splenocytes from mice with and those without nephritis led to renal disease in 4 of 5 recipients, without evidence of lung disease.

CONCLUSION

These findings indicate that RNP+CD4+ T cells are sufficient to induce anti-RNP autoimmunity, tissue targeting in anti-RNP autoimmunity can be deviated to either a renal or pulmonary phenotype depending on the presence of accessory cells such as myeloid DCs, and DC subsets can play a role in both propagation of autoimmunity and end-organ targeting.

Select T Cell Receptor Utilization by CD4+ T Cells in a Murine Model of Systemic Lupus Erythematosus is Similar to Human Disease (99.31)

Systemic lupus erythematosus (SLE) is a systemic autoimmune disease associated with significant morbidity and mortality. We have identified and characterized U1-70kDa small nuclear ribonucleoprotein (70kDa) autoantigen specific T cells in a murine model of autoimmunity when a subset of mice developed kidney disease similar to lupus nephritis. Mice developed proteinuria and histology showed CD4+ T cells associated with glomerular lesions. CD4+ T cells were freshly isolated from kidney and spleen and cultured with autoantigen to generate short-term T cell lines. Following RNA extraction from cell lines and cDNA preparation, a PCR reaction was performed using primers for the TRBV subgroups. The product was purified and underwent cloning and sequencing. T cell epitope mapping revealed that the majority of T cells were directed against antigenic peptides residing within the RNA binding domain of 70KDa. We also found that TCR beta (TRB) V usage was highly restricted among 70kDa reactive T cells which selectively utilized TCR BV subgroups 1 and 8.3 in the kidney and 1,2, 6, 8.1, 8.2, and 8.3 in the spleen and the lung. The TRB third complementary-determining regions (CDR3) had conserved sequence motifs which were shared across different TRBV subgroups. When compared for homology, the TRBV and CDR3 regions used by both murine and human 70kDa-specific CD4+ T cells were highly similar including those CD4+ T cells found at two sites of inflammation; the kidney and lung.

The NIH and Dept Veterans Affairs provided support for this work.

CD4+ T cells target epitopes residing within the RNA-binding domain of the U1-70-kDa small nuclear ribonucleoprotein autoantigen and have restricted TCR diversity in an HLA-DR4-transgenic murine model of mixed connective tissue disease

Mixed connective tissue disease (MCTD) is a systemic autoimmune disease with significant morbidity and premature mortality of unknown pathogenesis. In the present study, we characterized U1-70-kDa small nuclear ribonucleoprotein (70-kDa) autoantigen-specific T cells in a new murine model of MCTD. These studies defined 70-kDa-reactive T cell Ag fine specificities and TCR gene usage in this model. Similar to patients with MCTD, CD4(+) T cells can be readily identified from 70-kDa/U1-RNA-immunized HLA-DR4-transgenic mice. Using both freshly isolated CD4(+) T cells from spleen and lung, and T cell lines, we found that the majority of these T cells were directed against antigenic peptides residing within the RNA-binding domain of 70 kDa. We also found that TCR-beta (TRB) V usage was highly restricted among 70-kDa-reactive T cells, which selectively used TRBV subgroups 1, 2, 6, 8.1, 8.2, and 8.3, and that the TRB CDR3 had conserved sequence motifs which were shared across different TRBV subgroups. Finally, we found that the TRBV and CDR3 regions used by both murine and human 70-kDa-specific CD4(+) T cells were homologous. Thus, T cell recognition of the 70-kDa autoantigen by HLA-DR4-transgenic mice is focused on a limited number of T cell epitopes residing primarily within the RBD of the molecule, using a restricted number of TRBV and CDR3 motifs that are homologous to T cells isolated from MCTD patients.

Immune pathogenesis of Mixed Connective Tissue Disease: a short analytical review

Mixed Connective Tissue Disease (MCTD) was first described 35 years ago by Gordon C. Sharp and his colleagues. In the ensuing decades, a clearer understanding of the clinical and serologic features of MCTD has emerged. Classification criteria now exist to define MCTD for study purposes, the long-term outcome of the disease has been established, and novel genetic associations within the major histocompatibility complex on chromosome 6 and select regions on chromosome 3 have been identified. Studies on immune pathogenesis have made substantial progress in advancing our understanding of MCTD. In MCTD, there is a complex interaction of the innate and adaptive immune system that culminates in autoimmune disease. Antigenic structural modification occurring during apoptosis or other modifications of self antigens leads to an autoantigen driven immune process with innate immune activation, immunoglobulin G autoantibody production directed against select components of the spliceosome, B lymphocyte activation, and CD4 and CD8 T lymphocyte participation.

Clinical and immunologic manifestations of mixed connective tissue disease in a Miami population compared to a Midwestern US Caucasian population

OBJECTIVE

A cross-sectional study of mixed connective tissue disease (MCTD) was performed to determine if there were identifiable differences in the clinical expression of MCTD associated with race or ethnicity.

METHODS

Miami, Florida, and Midwestern US (Missouri) Caucasian MCTD cohorts were studied. Clinical and laboratory features of the 2 MCTD cohorts were compared. A concurrently collected cohort of Sm-positive patients with systemic lupus erythematosus (SLE) was studied as a control. Disease activity and severity and functional status were measured. CD4+CD25(high)-expressing T-regulatory cells were enumerated and serum soluble L selectin was measured as biomarkers of disease activity.

RESULTS

The Miami and Missouri Caucasian MCTD groups, while differing from the SLE group, were largely similar; however, gastroesophageal reflux, sclerodactyly, and malar rash were significantly more frequent in the Missouri MCTD group and alopecia was more frequent in the Miami MCTD group. Significant clinical and laboratory differences were found between the Miami MCTD and Miami SLE groups despite similar disease duration, activity, severity and functional status. Raynaud's phenomenon (RP), hand swelling, synovitis, myositis, and sclerodactyly were all significantly more common in RNP-positive MCTD versus Sm-positive SLE subjects. CONCLUSION Ethnic differences were observed in the frequency of end-organ involvement in the Miami MCTD versus the Missouri Caucasian MCTD groups. Clinical and laboratory features of all MCTD groups were clearly different from the SLE group, despite similar disease activity, disease severity, and functional status. Disease activity measures appeared to behave similarly as valid measures of disease activity in SLE and MCTD.

A Rasch analysis for classification of systemic lupus erythematosus and mixed connective tissue disease

The classification of rheumatic diseases is challenging because these diseases have protean and frequently overlapping clinical and laboratory manifestations. This problem is typified by the difficulty of classification and differentiation of two prototypic multi-system autoimmune diseases, Systemic Lupus Erythematosus (SLE) and Mixed Connective Tissue Disease (MCTD). The researchers submitted medical risk factor data represented by instrument or laboratory measures and physician judgments (12 key features for SLE) from 43 patients diagnosed with SLE and 12 key features for MCTD from 51 patients diagnosed with MCTD to the WINSTEPS Rasch analysis program. Using Rasch model parameterization, and fit and residuals analyses, the researchers identified separate dimensions for MCTD and SLE, thereby lending support to the position that MCTD is its own separate disease, distinct from SLE.

A Genome-Wide Study of Lupus: Preliminary Analysis and Data Release

Systemic lupus erythematosus (SLE) is a complex autoimmune disease in which genetics is one of the underlying risk factors. Complicating the analysis of SLE is the fact that the phenotype is heterogeneous, with variations in clinical features, and subgroups are associated with a variety of different autoantibodies. Many association studies of candidate genes as well as linkage studies have generated significant results, highlighting the multigenetic component of the disease. Those findings need to be replicated by independent laboratories and many other genes still remain to be identified. Here, we present our findings on the first genome-wide association study performed in 105 Caucasian patients and controls using the Affymetrix NspI array. The SLE patients studied here were all characterized by the presence of autoantibodies against the U1-6 small nuclear ribonucleoprotein antigen spliceosomal complex. Testing each SNP individually for association with disease, we identified 7 markers with an uncorrected P-value < 0.0001. Of those, three were in reported regions of linkage, namely 20p12, 2q37, and 4p15. To increase the power of our study, we included 60 controls corresponding to the parents from the publicly available CEPH families. The analysis of the 165 cases and controls leads to 28 SNPs being associated with an uncorrected P-value < 0.0001.

Differential tissue targeting of autoimmunity manifestations by autoantigen-associated Y RNAs

OBJECTIVE

To assess the Y RNAs, a family of homologous RNAs that bind to the Ro autoantigen, for the ability to contribute to autoimmune disease by activating RNA-responsive Toll-like receptors (TLRs).

METHODS

Using cell lines expressing or stably transfected with TLR-3, TLR-7, or TLR-8, we determined the patterns of RNA-specific TLR activation by in vitro transcripts of all of the known murine and human Y RNAs. Next, 8-10-week-old female mice were exposed to a single 50-microg subcutaneous injection of mouse Y1 or mouse Y3 RNA, and the effects were observed.

RESULTS

Y RNA family members differed in their TLR reactivities. Both human and mouse Y3 RNAs, but not other human or mouse Y RNAs, prominently induced TLR-3 activation. Although most human and mouse Y RNAs activated TLR-7 efficiently, mouse Y3 RNA and human Y5 RNA did not. Single subcutaneous injections of mice with either mouse Y1 RNA or mouse Y3 RNA induced or inhibited lymphoid infiltrates in different target organs based on the Y RNA and TLR status of the mouse used. Mouse Y1 RNA induced kidney lesions in TLR-3-intact mice but not in TLR-3-knockout mice. In contrast, mouse Y3 RNA treatment was associated with nephritis in TLR-3-knockout mice but not in TLR-3-intact mice. Sialoadenitis developed in untreated TLR-3-/- mice and in TLR-3-/- mice treated with mouse Y3 RNA, but sialoadenitis was not present in TLR--/-) mice treated with mouse Y1 RNA.

CONCLUSION

Y RNAs can induce innate immune responses and influence clinical manifestations of autoimmunity, suggesting that they are relevant to syndromes of anti-Ro autoimmunity. Distinct patterns of tissue targeting can be seen after exposure to different Y RNAs, in a pattern that correlates with the innate immune signals they induce. Thus, the balance of innate immune signals induced by exposure to endogenous Y RNAs may help determine the nature of the clinical syndrome in anti-Ro autoimmunity.

CD4+ T cells mediate autoimmune disease in a new transgenic murine model induced by U1 RNA and U1-70kD ribonucleoprotein self antigens (130.4)

C57BL/6 mice transgenic (Tg) for the human major histocompatibility complex gene HLA-DR4 were immunized with U1 RNA and a fusion protein spanning the RNA binding domain of the U1-70kD polypeptide, control fusion protein, with or without U1-RNA, or saline. Complete serologic and histologic analyses were performed on all mice. CD4+ T cells and APCs were isolated from immunized mice using immunoaffinity columns and tested for proliferation. Either freshly isolated CD4+ T cells from immunized mice or T cell lines were adoptively transferred to unmanipulated HLA-DR4 Tg or RAG−/− mice. Freshly isolated CD4+ T cell from immunized DR4 Tg mice proliferated in response to U1-70kD and to synthetic peptides from the RNA binding domain region of the protein in the presence of irradiated autologous APCs. We found that CD4+ T cells specific for U1-70kD were able to transfer disease to unmanipulated syngeneic mice. Furthermore, using purified CD4+ T cells or T cell lines specific for U1-70kD we were able to transfer disease to RAG−/− mice in the absence of detectable B cells or autoantibodies.

In conclusion, we have developed a new model of systemic autoimmunity that is induced following a single exposure to U1-RNA and its associated RNA binding protein. Anti-U1-70kD autoantigen-specfic CD4+ T cells appear to medicate pathogenesis of disease in this model and can do so in the absence of detectable B cells or autoantibodies.

This work was supported by NIH award AR43308 (RWH), the Lupus Foundation of American (RWH) and Department of Veterans Affairs Merit Review awards (RWH & ELG).

A murine model of mixed connective tissue disease induced with U1 small nuclear RNP autoantigen

OBJECTIVE

To test whether immunizing mice with autoantigens closely linked to mixed connective tissue disease (MCTD) could induce an MCTD-like clinical syndrome distinguishable from systemic lupus erythematosus (SLE).

METHODS

Transgenic and knockout C57BL/6-derived mice were immunized subcutaneously at age 8-12 weeks with U1-70-kd small nuclear RNP (70K) fusion protein along with either Freund's complete adjuvant (CFA) or U1 RNA. After 2 months, mice were killed and analyzed histologically and serologically.

RESULTS

Immunization of C57BL/6-derived mice transgenic for human HLA-DR4 with 70K and either CFA or U1 RNA led to anti-70K antibodies in 62% of mice (21 of 34), and diversified anti-RNP immune responses. MCTD-like lung disease also developed in 50% of immunized mice (17 of 34), and anti-70K antibodies were strongly correlated with lung disease. CFA and U1 RNA were comparably able to induce this syndrome. Mice deficient in Toll-like receptor 3 (TLR-3) also developed this same syndrome when immunized with 70K and CFA. However, TLR-3(-/-) mice failed to develop MCTD-like lung disease when treated with 70K and U1 RNA. Rather, TLR-3(-/-) mice immunized with 70K and U1 RNA developed an autoimmune syndrome characterized by glomerulonephritis typical of SLE.

CONCLUSION

Exposure to 70K in an appropriate context is sufficient to induce autoimmunity and target organ injury consistent with MCTD. This system represents a new model of autoimmune interstitial lung disease, and establishes a closer link between anti-70K immunity and MCTD-like lung disease. Of note, changes in innate immune signaling can cause the same trigger to lead to the development of SLE-like nephritis rather than MCTD-like lung disease.

Autoantibodies in the Pathogenesis of Mixed Connective Tissue Disease

Antibodies to U1-RNP are part of the clinical definition of mixed connective tissue disease (MCTD). These antibodies and other well-defined antibodies tend to arise together in affected patients. Although still speculative, hypotheses that link U1-RNP antibodies to the development of autoimmunity in MCTD and that associate U1-RNP antibodies with mechanisms of tissue injury in MCTD have emerged and are being tested. Salient features of these hypotheses include: (1) an antigen-driven response that is due to impaired clearance of potentially immunogenic self-antigens, (2) inadequate B- and T-cell tolerance to RNP autoantigens, and (3) immunogenic properties of the RNA component of targeted ribonucleoproteins. Further studies are needed to establish whether anti-RNP antibodies have prognostic importance that is relevant to practicing clinicians.

U1 RNA induces innate immunity signaling

OBJECTIVE

The U1-70-kd RNP is a prominent target of autoimmunity in connective tissue diseases. In this study, we explored whether its endogenous ligand, U1 RNA, mediates a proimmune signal and may be immunogenic.

METHODS

We assayed the proliferation of control and MyD88-knockout splenocytes in response to in vitro-synthesized U1 RNA, and measured interleukin-6 (IL-6) and IL-8 secretion induced by U1 RNA in a human cell line competent for signaling through Toll-like receptor 3 (TLR-3) and TLR-5.

RESULTS

Treatment with U1 RNA or with poly(I-C), a known agonist of TLR-3, induced approximately twice as much control splenocyte proliferation as did treatment with RNase-digested U1 RNA. Proliferation in response to either poly(I-C) or U1 RNA by MyD88-knockout splenocytes was similarly attenuated. Similar to poly(I-C), U1 RNA induced significant secretion of both IL-6 and IL-8 from a TLR-3-expressing human cell line; in contrast, the TLR-5 agonist flagellin induced predominantly IL-8 secretion. Pretreatment of U1 RNA with RNase abolished IL-6 and IL-8 secretion.

CONCLUSION

U1 RNA is capable of inducing manifestations consistent with TLR-3 activation. The ability of U1 RNA (which has a substantial double-stranded secondary structure) to activate TLR-3 may contribute to the immunogenicity of the U1-70-kd autoantigen. Stimulation of innate immunity by native RNA molecules with a double-stranded secondary structure may help explain the high prevalence of autoimmunity to RNA binding proteins.

T cells in the pathogenesis of systemic lupus erythematosus

Recent studies in patients with systemic lupus erythematosus (SLE) have demonstrated that autoantigen-reactive T cells can be isolated from peripheral blood and that such cells can support autoantibody production ex vivo, suggesting that they may have a central role in the pathogenesis of disease. In addition, recent work has identified and characterized signaling abnormalities in T cells from SLE that may be fundamental to the disease. This review will examine the role of T cells in the pathogenesis of SLE and it will consider pathogenic mechanisms by which T cells escape normal of immunological tolerance. The focus will be on recent studies characterizing autoantigen-reactive human T cells and signaling abnormalities identified in T cells from patients with SLE.

Human T cell clones specific for heterogeneous nuclear ribonucleoprotein A2 autoantigen from connective tissue disease patients assist in autoantibody production

OBJECTIVE

To identify and characterize human T cells reactive with heterogeneous nuclear RNP A2 (hnRNP A2) antigen, and to determine the ability of hnRNP-reactive T cells to assist in the production of human autoantibodies.

METHODS

T cells from patients with high serum levels of anti-hnRNP IgG autoantibody were stimulated with an hnRNP recombinant fusion protein, and the cells were cloned by limiting dilution. The surface phenotype and cytokine profiles of the T cells were examined by flow cytometry and enzyme-linked immunosorbent assay (ELISA), respectively. T cell clones were cultured with highly purified autologous B cells, and the ability of T cells to enhance autoantibody production under a variety of conditions was measured by ELISA.

RESULTS

Human T cells reactive with hnRNP antigen were cloned from 2 patients with systemic lupus erythematosus (SLE) and 1 patient with mixed connective tissue disease (MCTD). The T cells were CD4+ and had a Th1-like functional phenotype. In coculture in vitro with autologous B cells, T cell clones augmented anti-hnRNP autoantibody production and did so without the need for direct T cell-B cell contact.

CONCLUSION

This study provides direct evidence for a role of anti-hnRNP-reactive T cells in autoantibody production in SLE and MCTD. These findings support the notion that hnRNP-reactive T cells play a role in the pathogenesis of these diseases.

Cloned human TCR from patients with autoimmune disease can respond to two structurally distinct autoantigens

There is increasing evidence that the TCR can have significant plasticity in the range of Ags that a single receptor can recognize. Although it has been proposed that such TCR plasticity might contribute to autoimmunity, there have been few studies examining this possibility in either animal models or human disease. In the present study, we examined human T cell clones that were generated against two structurally dissimilar proteins, U1-70 kDa and Smith-B, that are physically associated in the U1-small nuclear ribonucleoprotein complex and that are frequent targets of autoantibodies and T cells in the same lupus patient. We found that the TCR from all clones isolated had substantial sequence homology within their complementarity-determining region 3. We molecularly cloned and expressed individual TCR/A and TCR/B genes in a TCR-negative human cell line J.RT3-T3.5. We then examined the interaction between the TCR and U1-70 kDa and Smith-B antigenic peptides. We found that there was plasticity or degeneracy of the TCR reactive with these lupus autoantigens in that two structurally dissimilar lupus autoantigenic peptides could stimulate a single TCR. These studies support an important role of plasticity of the TCR in the development of human autoimmunity.

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.

Apoptotic U1-70 kd is antigenically distinct from the intact form of the U1-70-kd molecule

OBJECTIVE

To determine whether immune responses to an apoptotically modified form of a human lupus autoantigen can be distinguished from immune responses to the intact form of the same antigen.

METHODS

Immunoblot and enzyme-linked immunosorbent assay techniques were used to test human autoimmune sera for the presence of antibodies to apoptotic forms of the U1- 70-kd small nuclear RNP antigen, while antibody recognition of intact U1-70 kd was blocked.

RESULTS

poptosis-specific U1-70-kd antibodies were identified by immunoblot in 15 of 29 sera with antibodies to intact U1-70 kd and in 2 of 25 sera without measurable antibodies to intact U1-70 kd. Bacterially produced, purified, caspase-cleaved U1-70 kd without additional posttranslational modifications was a target of apoptosis-specific antibodies in 3 of 9 U1-70-kd-positive sera tested.

CONCLUSION

The apoptotic form of U1-70 kd displays B cell epitopes that are not displayed on the intact form of U1-70 kd. Caspase cleavage in the absence of additional posttranslational modifications is sufficient to induce the display of some of these epitopes. Immunity to apoptotically modified proteins can develop against caspase-cleaved forms or against forms that undergo additional posttranslational modification.

Sicca symptoms and anti-SSA/Ro antibodies are common in mixed connective tissue disease

OBJECTIVE

To examine a large well characterized cohort of patients with mixed connective tissue disease (MCTD) and determine longitudinally the prevalence of clinical and serologic features of Sjogren's syndrome in these patients.

METHODS

Patients were followed longitudinally up to 30 years with systematic clinical and serologic analysis. Sera were analyzed for reactivity with SSA/Ro, SSB/La, and snRNP polypeptide U1-70kD and for anticardiolipin antibodies.

RESULTS

Among a well characterized patient population with MCTD, 18/55 (32.7%) had antibodies to SSA/Ro, while 2/55 (3.6%) had antibodies to SSB/La, either initially or during the course of followup. All patients had antibodies to U1-70kD small nuclear ribonucleoprotein antigen. Sicca symptoms were common, occurring in 23/55 (41.8%) patients. Patients with MCTD who were anti-SSA/Ro positive had increased incidence of malar rash (p < 0.03) and photosensitivity (p < 0.001) compared to anti-SSA/Ro negative patients.

CONCLUSION

Sicca symptoms are frequent in patients with MCTD, occurring in up to one-third of the patients studied. The presence of anti-SSA/Ro antibodies identifies a group of MCTD patients with a very high incidence of malar rash and photosensitivity.

T cells in the pathogenesis of systemic lupus erythematosus

The role of T cells in the pathogenesis of systemic lupus erythematosus (SLE) is reviewed with a focus on autoantigen-specific T cells in SLE. The initial clue to a role for T cells in SLE was histopathologic studies demonstrating extensive infiltration of T cells at the sites of inflammation. Later studies, showing association between HLA polymorphisms and specific autoantibodies, directly implicated a role for T cells in autoantibody production. More recently, we and others have identified and characterized autoantigen-specific T cells in SLE. We review these studies on the role of autoantigen-specific T cells in SLE and present new findings on the molecular characterization of T cell immunity to Sm-B, Sm-D and U1-70kD small nuclear ribonucleoprotein (snRNP) autoantigens.

Structural analysis of TCRalpha and beta chains from human T-Cell clones specific for small nuclear ribonucleoprotein polypeptides Sm-D, Sm-B and U1-70 kDa: TCR complementarity determining region 3 usage appears highly conserved

Systemic lupus erythematosus (SLE) and mixed connective tissue disease (MCTD) are systemic autoimmune diseases that are characterized by the presence of autoantibodies reactive with U small nuclear RNP (snRNP) autoantigens. Both B and T cells are important in the pathogenesis of the disease, and T- and B-cell immunity against snRNP polypeptides have been shown to be linked in vivo. Currently, several alternative hypotheses for the pathogenesis of these diseases have been proposed. These include loss of tolerance, modified self-antigens, molecular mimicry and nondirected immune activation. To help distinguish between the various models of disease pathogenesis, we have characterized the T-cell receptor (TCR) CDR3 from a large panel of well-characterized human T-cell clones and lines specific for individual snRNP polypeptides. The results presented here reveal highly restricted TCR usage across patients by the snRNP-reactive T cells based on the deduced amino acid sequence of the CDR3 loop. These data support the hypothesis that T-cell responses against self antigens in SLE and MCTD are antigen driven and that there are a limited number of T-cell epitopes present on the snRNP autoantigens.

T cell epitope mapping of the Smith antigen reveals that highly conserved Smith antigen motifs are the dominant target of T cell immunity in systemic lupus erythematosus

B cell and T cell immunity to the Smith Ag (Sm) is a characteristic feature of systemic lupus erythematosus (SLE). We have shown that T cell immunity against Sm can be detected in SLE patients, and that T and B cell immunity against Sm are linked in vivo. TCR usage by Sm-reactive T cells is highly restricted and characteristic of an Ag-driven immune response. Sm is a well-characterized complex Ag consisting of proteins B1, B2, D1, D2, D3, E, F, and G. A unique feature of all Sm proteins is the presence of homologous motifs, Sm motif 1 and Sm motif 2. We used limiting dilution cloning and synthetic peptide Ags to characterize the human T cell immune response against Sm in seven SLE patients. We sought to determine the precise antigenic peptides recognized, the common features of antigenic structure recognized, and the evolution of the T cell response against Sm. We found there was a highly restricted set of Sm self-peptides recognized by T cells, with three epitopes on Sm-B and two epitopes on Sm-D. We found that T cell immunity against Sm-B and Sm-D was encoded within the highly conserved Sm motif 1 and Sm motif 2, and that immunity against these epitopes appeared stable. The present study supports the concept that T cell immunity to Sm is an Ag-driven immune response directed against a highly restricted set of self-peptides, encoded within Sm motif 1 and Sm motif 2, that is shared among all Sm proteins.

Immunization with a bacterial ATP-binding cassette transporter fragment suppresses autoimmunity and prolongs survival in MRL/lpr lupus-prone mice

The present study was undertaken to better define the role of the U1 70 kDa antigen in a spontaneous murine model of systemic lupus erythematosus (SLE) by testing whether immunization with the U1 70 kDa polypeptide could alter the production of antibodies against U1 70 kDa or against other small nuclear ribonucleoproteins (snRNP), modify disease expression or alter survival. We found that, while immunization with a U1 70 kDa derived fusion protein (70 KFP) tended to delay the development of anti-snRNP antibodies in the sera of MRL/lpr mice, it had no effect on autoimmune-mediated renal disease or survival. Unexpectedly, it was found that MRL/lpr mice immunized with a 367 amino acid fragment of a bacterial ATP-binding cassette transporter, MFP, had prolonged survival compared to saline injection or U1 70 kDa immunization and that this was associated with a delay in the onset of SLE-like proliferative glomerulonephritis. This is the first study, to our knowledge, in which a bacterial ATP-binding cassette transporter was shown to be beneficial in treating a murine model of SLE. We report that MFP significantly prolonged longevity in the MRL/lpr murine model of SLE compared to saline injection or 70 KFP immunization and that improved survival was associated with a delay in the onset of SLE-like glomerulonephritis.

The appearance of U1 RNP antibody specificities in sequential autoimmune human antisera follows a characteristic order that implicates the U1-70 kd and B'/B proteins as predominant U1 RNP immunogens

OBJECTIVE

To observe the order of development of anti-U1 RNP peptide antibodies in humans.

METHODS

Immunoblots against Jurkat cell lysates were performed on 5,882 serum samples from 3,668 patients referred on clinical grounds for RNP antibody testing to a reference laboratory between 1989 and 1999. In patients from whom multiple samples were drawn, we determined the order in which IgG antibodies to the U1 RNP peptides A, B'/B, C, D, and 70 kd appeared.

RESULTS

One hundred sixty-three patients with serial samples were identified in whom antibodies to at least one U1 RNP peptide initially were not present but later appeared. The first RNP antibodies to appear were most often directed against the 70 kd and B'/B peptides (P < 0.01). Antibodies to the A and C peptides usually developed after other RNP peptide antibodies, and antibodies to D often emerged only after immunity to multiple other U1 RNP proteins had appeared. B'/B, but not 70 kd, was a frequent early target of spreading after initial immunity to other RNP peptides.

CONCLUSION

Orderly patterns of emergence of U1 RNP peptide antibodies appear to exist in humans. Two peptides, 70 kd and B'/B, show characteristics of early immunogens in the development of human RNP immunity.

Mixed connective tissue disease

A defining feature of mixed connective tissue disease (MCTD) is the presence of antibodies against the U1-ribonucleoprotein (RNP) complex, but other autoantibodies in MCTD have recently been described. Research has also further elucidated the immune responses directed against U1-RNP in humans and in murine models of disease. Hypotheses implicating modified self-antigens and/or infectious agents in the pathogenesis of MCTD have been advanced. Links between the immunologic and clinical phenomena in MCTD are emerging. Longitudinal study of patients with MCTD highlights the impact of pulmonary hypertension on disease outcome.

Autoantibody recognition of distinctly modified forms of the U1-70-kd antigen is associated with different clinical disease manifestations

OBJECTIVE

To examine whether autoantibody recognition of modified forms of the U1-70-kd RNP antigen correlates with manifestations of rheumatic disease.

METHODS

Blinded to clinical disease manifestations, sera from 27 rheumatic disease patients with U1-70-kd antibodies were used to immunoblot control, apoptotic, and oxidatively modified HeLa cell lysates. Using densitometry, recognition of antigen fragments was quantitated. The presence or absence of 1) lupus skin disease and 2) Raynaud's phenomenon (RP) was determined for each patient by chart review. The ability of patient sera to recognize the different fragments was compared for patients with and without skin disease and with and without RP.

RESULTS

Patients with lupus skin disease had higher recognition of apoptotic U1-70 kd than did patients without skin disease (mean +/- SD fragment recognition index [FRI] 1.35 +/- 0.57 versus 0.95 +/- 0.25; P < 0.024, by Student's t-test). Patients with RP had higher recognition of oxidatively modified U1-70 kd than did patients without RP (mean +/- SD FRI 0.95 +/- 0.80 versus 0.24 +/- 0.22; P < 0.048).

CONCLUSION

Recognition of apoptotically and oxidatively modified forms of the U1-70-kd autoantigen are associated with distinct clinical rheumatic disease manifestations. This finding provides in vivo evidence for the hypothesis that immune recognition of modified forms of self antigens may be relevant to the pathogenesis of systemic rheumatic diseases. Understanding the antigenic modifications to which patients react may help predict the expression of rheumatic syndromes.