Conservation of pathogenic TCR homology across class II restrictions in anti-ribonucleoprotein autoimmunity: extended efficacy of T cell vaccine therapy.

T cells have been shown to mediate aspects of anti-ribonucleoprotein (RNP) autoimmunity, and are a potential target of therapy in lupus and related diseases. In this study, we assessed the relevance of a conserved class of anti-RNP T cells to autoimmune disease expression and therapy. Our data show that anti-RNP T cell selection induced a limited set of homologous CDR3 motifs at high frequency. Homologous CDR3 motifs have been reported in other autoimmune diseases. Vaccination with irradiated anti-RNP (but not anti-tetanus toxoid) CD4(+) cells induced remission of anti-RNP-associated nephritis in ≥ 80% of treated mice, even with donor/recipient MHC class II mismatch, and in both induced and spontaneous autoimmunity. Vaccine responder sera inhibited anti-70k T cell proliferation and bound hybridomas expressing the conserved CDR3 motifs. Our data indicate that a limited set of TCR CDR3 motifs may be important for the pathogenesis of anti-RNP lupus and other autoimmune diseases. The ability to target a consistent set of pathogenic T cells between individuals and across class II restrictions may allow for the more practical development of a standardized anti-RNP T cell vaccine preparation useful for multiple patients.

Impaired B Cell Apoptosis Results in Autoimmunity That Is Alleviated by Ablation of Btk.

While apoptosis plays a role in B-cell self-tolerance, its significance in preventing autoimmunity remains unclear. Here, we report that dysregulated B cell apoptosis leads to delayed onset autoimmune phenotype in mice. Our longitudinal studies revealed that mice with B cell-specific deletion of pro-apoptotic Bim (BBimfl/fl ) have an expanded B cell compartment with a notable increase in transitional, antibody secreting and recently described double negative (DN) B cells. They develop greater hypergammaglobulinemia than mice lacking Bim in all cells and accumulate several autoantibodies characteristic of Systemic Lupus Erythematosus (SLE) and related Sjögren's Syndrome (SS) including anti-nuclear, anti-Ro/SSA and anti-La/SSB at a level comparable to NODH2h4 autoimmune mouse model. Furthermore, lymphocytes infiltrated the tissues including submandibular glands and formed follicle-like structures populated with B cells, plasma cells and T follicular helper cells indicative of ongoing immune reaction. This autoimmunity was ameliorated upon deletion of Bruton's tyrosine kinase (Btk) gene, which encodes a key B cell signaling protein. These studies suggest that Bim-mediated apoptosis suppresses and B cell tyrosine kinase signaling promotes B cell-mediated autoimmunity.

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.

Increased Risk of Ischemic Stroke in Systemic Sclerosis: A National Cohort Study of US Veterans.

OBJECTIVE: Previously thought to involve primarily the microvasculature, systemic sclerosis (SSc) has been increasingly linked to macrovascular disease. Cardiovascular (CV) and cerebrovascular disease are responsible for 20-30% of mortality in SSc, but few studies have shown an independent association between SSc and stroke. We assessed whether SSc was an independent risk factor for ischemic stroke. METHODS: We conducted a retrospective cohort study using the national Veterans Affairs (VA) administrative database containing records from 1999 to 2014. We obtained data for all patients with a diagnosis of SSc as well as 2 controls per SSc patient matched on sex, race, smoking status, and VA site. All patients were followed until development of ischemic stroke, death, or last encounter. We used a Cox proportional hazard regression model to estimate risk of ischemic stroke, with adjustments for CV comorbidities (hypertension, diabetes, atrial fibrillation, non-cerebrovascular atherosclerotic disease, hyperlipidemia), baseline medication use (aspirin, nonsteroidal antiinflammatory drugs), and Medicare enrollment. RESULTS: Among 4545 individuals with SSc (83% male, mean age 60.9 yrs), the incidence rate of ischemic stroke was 15.3 per 1000 person-years (vs 12.2 in the control cohort), with an unadjusted HR 1.28 (95% CI 1.11-1.47). The adjusted HR was 1.21 (95% CI 1.05-1.40) after adjusting for baseline CV risk factors, medications, and Medicare enrollment. CONCLUSION: SSc is independently associated with a higher risk of ischemic stroke among US veterans. Patients with SSc represent a population likely to benefit from targeted stroke screening or prevention therapies.

Endosomal Toll-like receptors in autoimmunity: mechanisms for clinical diversity.

The endosomal Toll-like receptors (TLR3, TLR7 and TLR9) have been implicated in the pathogenesis of autoimmune diseases. Their signaling pathways show remarkable similarities and yet the outcomes following activation of each of these TLRs lead to clinically distinct autoimmune disease phenotypes. This review discusses how differences may arise at a molecular and cellular level to account for this diversity of responses. Understanding the roles of individual TLR pathways and the relationships between them and non-TLR innate immune pathways in the pathogenesis of diseases such as systemic lupus erythematosis highlights potential treatment targets for this spectrum of autoimmune diseases.

Recent advances and opportunities in research on lupus: environmental influences and mechanisms of disease.

OBJECTIVES: In this review we summarize research on mechanisms through which environmental agents may affect the pathogenesis of lupus, discuss three exposures that have been the focus of research in this area, and propose recommendations for new research initiatives. DATA SOURCES AND SYNTHESIS: We examined studies pertaining to key mechanistic events and specific exposures. Apoptosis leading to increased production or decreased clearance of immunogenic intracellular self-antigens and defective apoptosis of autoreactive immune cells both have been implicated in the loss of self-tolerance. The adjuvant or bystander effect is also needed to produce a sustained autoimmune response. Activation of toll-like receptors is one mechanism through which these effects may occur. Abnormal DNA methylation may also contribute to the pathogenesis of lupus. Each of the specific exposures we examined--Epstein-Barr virus, silica, and trichloroethylene--has been shown, in humans or in mice, to act upon one or more of these pathogenic steps. Specific recommendations for the continued advancement of our understanding of environmental influences on lupus and other autoimmune diseases include the development and use of mouse models with varying degrees of penetrance and manifestations of disease, identification of molecular or physiologic targets of specific exposures, development and use of improved exposure assessment methodologies, and multisite collaborations designed to examine understudied environmental exposures in humans. CONCLUSIONS: The advances made in the past decade concerning our understanding of mechanisms involved in the development of lupus and the influence of environmental agents on this process provide a strong foundation for further developments in this field.

Anti-ribonucleoprotein antibodies mediate enhanced lung injury following mesenteric ischemia/reperfusion in Rag-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.

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.

Ultraviolet radiation damages self noncoding RNA and is detected by TLR3.

Exposure to ultraviolet B (UVB) radiation from the sun can result in sunburn, premature aging and carcinogenesis, but the mechanism responsible for acute inflammation of the skin is not well understood. Here we show that RNA is released from keratinocytes after UVB exposure and that this stimulates production of the inflammatory cytokines tumor necrosis factor α (TNF-α) and interleukin-6 (IL-6) from nonirradiated keratinocytes and peripheral blood mononuclear cells (PBMCs). Whole-transcriptome sequencing revealed that UVB irradiation of keratinocytes induced alterations in the double-stranded domains of some noncoding RNAs. We found that this UVB-damaged RNA was sufficient to induce cytokine production from nonirradiated cells, as UVB irradiation of a purified noncoding RNA (U1 RNA) reproduced the same response as the one we observed to UVB-damaged keratinocytes. The responses to both UVB-damaged self-RNAs and UVB-damaged keratinocytes were dependent on Toll-like receptor 3 (TLR3) and Toll-like receptor adaptor molecule 1 (TRIF). In response to UVB exposure, Tlr3(-/-) mice did not upregulate TNF-α in the skin. Moreover, TLR3 was also necessary for UVB-radiation-induced immune suppression. These findings establish that UVB damage is detected by TLR3 and that self-RNA is a damage-associated molecular pattern that serves as an endogenous signal of solar 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.

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.

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.

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.

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.

Patients with antibodies to both PmScl and dsDNA.

OBJECTIVE: To determine the significance of dsDNA antibodies in patients with antibodies to PmScl. METHODS: All patients testing positive for PmScl and/or dsDNA antibodies at an academic medical center between 1977 and 2002 were identified. Charts for the PmScl-positive patients were reviewed for manifestations of lupus, scleroderma, or polymyositis/dermatomyositis. Patients with antibodies to dsDNA were matched to each of the double-positive PmScl+/dsDNA+ patients on the basis of sex, race, age, and date of autoantibody testing. Standard classification criteria for lupus, scleroderma, and myositis were used (excluding dsDNA, PmScl, or antinuclear antibodies as criteria), and the number of subjects meeting classification criteria was recorded. RESULTS: Records were available for 38 out of 47 patients who were identified as PmScl-positive. The prevalence of dsDNA antibodies in this group was 42% (16/38). Patients with PmScl and dsDNA antibodies had a higher prevalence of systemic lupus erythematosus (8/16 vs 2/22; p = 0.008) and a lower rate of scleroderma or myositis (1/16 vs 9/22; p = 0.025) than dsDNA-negative patients with PmScl antibodies. The prevalence of systemic lupus erythematosus, myositis, and scleroderma in patients with PmScl and dsDNA antibodies was not different from the prevalences of these diseases in a matched cohort of patients who were dsDNA-positive. CONCLUSION: Antibodies to PmScl are associated with scleroderma and myositis when dsDNA antibodies are not present. In the presence of dsDNA antibodies, PmScl antibodies do not appear to have clinical relevance.

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.

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.

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.

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.