Risk Factor For Pulmonary Fibrosis Research Articles

Diagnostic and Predictive Significance of Serum MiR-141-3p in Acute Respiratory Distress Syndrome Patients with Pulmonary Fibrosis.

Pulmonary fibrosis (PF) is the major complication and death-related factor of acute respiratory distress syndrome (ARDS). This study evaluated the significance of miR-141-3p in ARDS and its complication of PF aiming to identify a potential biomarker for screening ARDS and predicting the occurrence of PF. A total of 137 ARDS patients and 69 healthy individuals were enrolled in this study and the serum samples were collected from all participants. The serum miR-141-3p levels were analyzed by polymerase chain reaction. The significance of miR-141-3p in the diagnosis and development of ARDS, and the occurrence of PF was evaluated by receiver operating curve, Chi-square test, and logistic regression analysis. MiR-141-3p was downregulated in ARDS patients and showed significant potential in its diagnosis. Reduced miR-141-3p was significantly associated with the increasing Murray and APACHEII score and the occurrence of PF in ARDS patients. MiR-141-3p, Murray score, and APACHEII score were identified as risk factors for the occurrence of PF in ARDS, and miR-141-3p was also found to be downregulated in ARDS patients with PF. Additionally, miR-141-3p could discriminate ARDS patients with PF and without PF, and was closely associated with the decreased total lung capacity, carbon monoxide diffusing capacity, and forced vital capacity of ARDS patients with PF. Downregulated miR-141-3p served as a biomarker for ARDS screening disease onset and indicating the severity. Reduced miR-141-3p was also identified as a risk factor for PF in ARDS patients and was associated with the severe progression of PF.

Proteomic analysis reveals the aging-related pathways contribute to pulmonary fibrogenesis.

Aging usually causes lung-function decline and susceptibility to chronic lung diseases, such as pulmonary fibrosis. However, how aging affects the lung-fibrosis pathways and leads to the occurrence of pulmonary fibrosis is not completely understood. Here, mass spectrometry-based proteomics was used to chart the lung proteome of young and old mice. Micro computed tomography imaging, RNA immunoprecipitation, dual-fluorescence mRFP-GFP-LC3 adenovirus monitoring, transmission electron microscopy, and other experiments were performed to explore the screened differentially expressed proteins related to abnormal ferroptosis, autophagy, mitochondria, and mechanical force in vivo, in vitro, and in healthy people. Combined with our previous studies on pulmonary fibrosis, we further demonstrated that these biological processes and underlying molecular players were also involved in the aging process. Our work depicted a comprehensive cellular and molecular atlas of the aging lung and attempted to explain why aging is a risk factor for pulmonary fibrosis and the role that aging plays in the progression of pulmonary fibrosis. The abnormalities of aging triggered an increase in mechanical force and ferroptosis, autophagy blockade, and mitochondrial dysfunction, which often appear during pulmonary fibrogenesis. We hope that the elucidation of these anomalies will help to enhance our understanding of senescence-inducing pulmonary fibrosis, thereby guiding the use of anti-senescence as an entry point for early intervention in pulmonary fibrosis and age-related diseases.

Are MUC5B and TERT mutations genetic risk factors for pulmonary fibrosis in individuals with severe COVID-19?

The genetic risk factors for Coronavirus disease-2019 (COVID19)-associated pulmonary fibrosis (CAPF) are not clearly defined. Mutations in the genes encoding telomerase reverse transcriptase (TERT) and mucin 5B (MUC5B) are well-known genetic risk factors for pulmonary fibrosis. In this study, we aimed to show whether the most common proven mutations of pulmonary fibrosis affect the development of CAPF. Forty-eight patients who were matched for age, gender, COVID-19 disease severity, and respiratory support type and needed high flow nasal cannula, non-invasive mechanical ventilator, or invasive mechanical ventilator due to COVID-19 were followed up prospectively. Eighteen patients were excluded from the follow-up due to known structural lung disease, collagen tissue disease, and occupational exposure to fibrosis. The patients were called for follow-up three months after discharge, and CT was performed. Those with fibrosis (n= 15) in the third-month follow-up CT were included in the CAPF group, and those with complete resolution (n= 15) were included in the control group. Blood samples were taken for genetic analysis. TERT gene study revealed that six (40%) of the fibrosis group was normal, while five were heterozygous (33.3%). MUC5B polymorphism was not detected in 10 (66.7%) of the fibrosis group. Individuals with TERT mutations may be at a higher risk for CAPF. Further studies are needed to clarify the genetic risk factors for CAPF.

Retraction Note to: Type 1 Diabetes Mellitus is an Independent Risk Factor for Pulmonary Fibrosis.

Retraction Note to: Type 1 Diabetes Mellitus is an Independent Risk Factor for Pulmonary Fibrosis.

Prognostic Factors for Pulmonary Fibrosis Following Pneumonia in Patients with COVID-19: A Prospective Study

The frequency and clinical manifestation of lung fibrosis accompanied by coronavirus disease (COVID-19) are not well-established. We aimed to identify the factors attributed to post-COVID-19 fibrosis. This single-center prospective study included patients diagnosed with COVID-19 pneumonia from 12 April to 22 October 2021 in the Republic of Korea. The primary outcome was the presence of pulmonary fibrosis on a CT scan 3 months after discharge; the fibrosis risk was estimated by a multiple logistic regression. The mean patient age was 55.03 ± 12.32 (range 27–85) years; 65 (66.3%) were men and 33 (33.7%) were women. The age, Charlson Comorbidity Index, lactate dehydrogenase level, aspartate aminotransferase level, and Krebs von den Lungen-6 level were significantly higher and the albumin level and the saturation of the peripheral oxygen/fraction of inspired oxygen (SpO2/FiO2) ratio were significantly lower in the fibrosis group than in the non-fibrosis group; the need for initial oxygen support was also greater in the fibrosis group. An older age (adjusted odds ratio (AOR) 1.12; 95% confidence interval (CI) 1.03–1.21) and a lower initial SpO2/FiO2 ratio (AOR 7.17; 95% CI 1.72–29.91) were significant independent risk factors for pulmonary fibrosis after COVID-19 pneumonia. An older age and a low initial SpO2/FiO2 ratio were crucial in predicting pulmonary fibrosis after COVID-19 pneumonia.

Interstitial Lung Fibrosis Following COVID-19 Pneumonia.

Background and Objectives: Pulmonary fibrosis represents a stage of normal physiologic response to inflammatory aggression, mostly self-limiting and reversible; however, numerous patients treated for SARS-CoV-2 pneumonia present after release from hospital residual lung fibrosis. In this article, we aim to present an optimization method for evaluating pulmonary fibrosis by quantitative analysis, to identify the risk factors/predictors for pulmonary fibrosis in patients with SARS-CoV-2 infection, and to characterize the impact of pulmonary fibrosis on the symptomatology of patients after release from the hospital. Materials and Methods: We performed a prospective observational study on 100 patients with severe forms of pneumonia, with a control group of 61 non-COVID normal patients. Results: We found persistent interstitial changes consistent with fibrotic changes in 69% of patients. The risk of fibrosis was proportional to the values of erythrocyte sedimentation rate (ESR), C reactive protein (CRP), and lactate dehydrogenase (LDH), and to the duration of hospitalization. The imaging parameters correlated with increased risk for interstitial fibrosis were the number of affected pulmonary lobes and the percent of interstitial pulmonary fibrosis. Conclusions: The main risk factors for pulmonary fibrosis post-COVID-19 identified in our study are increased ESR, CRP, LDH, duration of hospitalization and the severity of pneumonia.

IDIOPATHIC CHRONIC EOSINOPHILIC PNEUMONIA EVOLVING TO PULMONARY FIBROSIS: A RETROSPECTIVE ANALYSIS

TOPIC: Diffuse Lung Disease TYPE: Original Investigations PURPOSE: Some patients with idiopathic chronic eosinophilic pneumonia (ICEP) may develop pulmonary fibrosis. This study was conducted to investigate the predictors of fibrosis developing in patients with ICEP. METHODS: A retrospective, computer-assisted search was performed to identify patients with ICEP seen at Mayo Clinic, Rochester from 1997-2019. Those patients who had follow-up chest CT beyond 12 months after the ICEP diagnoses were included in the study. Demographics, clinical, radiologic, and histopathologic features were analyzed. Proportional hazards regression was used to assess the predictors of pulmonary fibrosis. RESULTS: We identified 68 patients; mean±SD age at the time of ICEP diagnosis was 56.4±13.2 years, 60% female. Cough (87%) followed by shortness of breath (84%) and wheezing (35%) were the most common presenting symptoms. 41% had history of smoking and 46% had history of asthma. During follow-up 29 patients (43%) developed CT evidence of pulmonary fibrosis; 76% of these patients had a CT pattern inconsistent with usual interstitial pneumonia (UIP) pattern. The CT evidence of pulmonary fibrosis developed within 2 years after the diagnosis of ICEP in the majority of these patients. Age, body mass index (BMI) and male sex were the predictors of pulmonary fibrosis. On the other hand, history of asthma decreased the likelihood of developing pulmonary fibrosis. CONCLUSIONS: Development of pulmonary fibrosis is not uncommon in patients with ICEP, especially in older males with high BMI, and is associated with an increased risk of mortality. CLINICAL IMPLICATIONS: The clinical implication of our study is to recognize this phenomenon and to keep following up patients with ICEP especially those with risk factors for pulmonary fibrosis. Early institution of prednisone should be considered. DISCLOSURES: No relevant relationships by Misbah Baqir, source=Web Response No relevant relationships by Tucker Johnson, source=Web Response No relevant relationships by Tobias Peikert, source=Web Response No relevant relationships by Jay Ryu, source=Web Response No relevant relationships by Darrell Schroeder, source=Web Response No relevant relationships by Joanne Yi, source=Web Response

Pulmonary fibrosis in non-mutation carriers of families with short telomere syndrome gene mutations.

Diagnostic and predictive genetic testing for disease cause and risk estimation is common in many countries. For genetic diseases, predictive test results are commonly straightforward: presence of the mutation involves increased risk for disease and absence of the mutation involves no inherit risk for disease. Germline mutations in telomere-related genes (TRGs) can lead to telomere shortening and are associated with short telomere syndrome (STS). Telomere length is heritable, and in families with STS due to a TRG mutation, progeny with and without the TRG mutation is known to have shorter than average telomeres. We hypothesize that progeny of TRG mutation carriers who did not inherit the TRG mutation may still develop pulmonary fibrosis. A genetic screen of 99 unrelated families with familial pulmonary fibrosis revealed five patients with features of pulmonary fibrosis but without carrying the familial disease-causing TRG mutation. Features of STS were present in each family, including short telomeres in blood and tissue of the non-mutation carrying patients. Additional genetic, clinical or environmental risk factors for pulmonary fibrosis were present in each non-mutation carrying patient. Our study shows that non-mutation carrying first-degree relatives in families with STS are at increased risk for pulmonary fibrosis. Disease development may be triggered by inherited short telomeres and additional risk factors for disease. This observation has profound consequences for genetic counselling. Unlike any other genetic syndrome, absence of the mutation does not imply absence of disease risk. Therefore, clinical follow-up is still urged for non-mutation carrying first-degree family members.

Lifetime risk of rheumatoid arthritis-associated interstitial lung disease in MUC5B mutation carriers

ObjectivesTo estimate lifetime risk of developing rheumatoid arthritis-associated interstitial lung disease (RA-ILD) with respect to the strongest known risk factor for pulmonary fibrosis, a MUC5B promoter variant.MethodsFinnGen is a collection...

The characteristics and evolution of pulmonary fibrosis in COVID-19 patients as assessed by AI-assisted chest HRCT.

The characteristics and evolution of pulmonary fibrosis in patients with coronavirus disease 2019 (COVID-19) have not been adequately studied. AI-assisted chest high-resolution computed tomography (HRCT) was used to investigate the proportion of COVID-19 patients with pulmonary fibrosis, the relationship between the degree of fibrosis and the clinical classification of COVID-19, the characteristics of and risk factors for pulmonary fibrosis, and the evolution of pulmonary fibrosis after discharge. The incidence of pulmonary fibrosis in patients with severe or critical COVID-19 was significantly higher than that in patients with moderate COVID-19. There were significant differences in the degree of pulmonary inflammation and the extent of the affected area among patients with mild, moderate and severe pulmonary fibrosis. The IL-6 level in the acute stage and albumin level were independent risk factors for pulmonary fibrosis. Ground-glass opacities, linear opacities, interlobular septal thickening, reticulation, honeycombing, bronchiectasis and the extent of the affected area were significantly improved 30, 60 and 90 days after discharge compared with at discharge. The more severe the clinical classification of COVID-19, the more severe the residual pulmonary fibrosis was; however, in most patients, pulmonary fibrosis was improved or even resolved within 90 days after discharge.

High-resolution CT in smoking-related interstitial lung diseases.

In addition to chronic obstructive pulmonary disease (COPD) and bronchogenic carcinoma, smoking can also cause interstitial lung diseases (ILDs) such as respiratory bronchiolitis (RB), RB with ILD (RB-ILD), desquamative interstitial pneumonia (DIP), Langerhans cell granulomatosis (LCG) and idiopathic pulmonary fibrosis-usual interstitial pneumonia (IPF-UIP). However, smoking seems to have a protective effect against hypersensitivity pneumonitis (HP), sarcoidosis and organising pneumonia (OP). High-resolution computed tomography (HRCT) has a pivotal role in the differential diagnosis. RB is extremely frequent in smokers, and is considered a marker for smoking exposure. It has no clinical relevance in itself since most patients with RB are asymptomatic. It is frequent to observe the association of RB with other smoking-related diseases, such as LCG or pulmonary neoplasms. In RB-ILD, HRCT features are more conspicuous and diffuse than in RB, but there is no definite cut-off between the two entities and any distinction can only be made by integrating imaging and clinical data. RB, RB-ILD and DIP may represent different degrees of the same pathological process, consisting in a bronchiolar and alveolar inflammatory reaction to smoking. Smoking is also a well-known risk factor for pulmonary fibrosis. Multidisciplinary discussion and follow-up can generally solve even the most difficult cases.

Progress in respiratory toxicity of polyhexamethyleneguaidine disinfectant and mechanism exploration

Polyhexamethylene guanidine (PHMG) is a high molecular guanidine compound with a broad spectrum of antibacterial effects. Since the outbreak of the 'humidifier disinfectant-induced lung injury' event in South Korea, the respiratory toxicity of PHMG had become a public concern. An epidemiological survey in Korea found that PHMG-containing disinfectants were an important risk factor for pulmonary fibrosis. Animal experiments also showed that the exposure to PHMG through the respiratory tract could cause irreversible fibrosis in the lungs. TGF-β signaling pathway, epithelial-mesenchymal transition and pulmonary inflammation might be the main pathways that could mediate PHMG-induced pulmonary fibrosis. This article provided an overview of the characteristics of population exposure to PHMG and research progress in the field of respiratory toxicology and recommendations for the rational and standard of using PHMG-related products in China.

IFNL3 genotype is associated with pulmonary fibrosis in patients with systemic sclerosis

Fibrosis across different organs and tissues is likely to share common pathophysiological mechanisms and pathways. Recently, a polymorphism (rs12979860) near the interferon lambda gene (IFNL3) was shown to be associated with fibrosis in liver across multiple disease etiologies. We determined whether this variant is a risk factor for pulmonary fibrosis (PF) and worsening cutaneous fibrosis in systemic sclerosis (SSc). Caucasian patients with SSc (n = 733) were genotyped to test for association with the presence of PF and worsening of skin fibrosis. Serum IFN-λ3 levels from 200 SSc cases were evaluated. An association of the IFNL3 polymorphism with PF was demonstrated (OR: 1.66 (95% CI: 1.142–2.416, p = 0.008). The IFNL3 variant was not a risk factor for worsening of skin fibrosis. Functionally, IFN-λ3 serum levels were higher among subjects with PF compared to those unaffected (P < 0.0001). In conclusion, IFNL3 serum levels and the genetic variant known to be associated with liver fibrosis are similarly linked to PF, but not to worsening of skin fibrosis in SSc. These data highlight both common fibrosis pathways operating between organs, as well as differential effects within the same disease.

Cigarette smoke exposure combined with lipopolysaccharides induced pulmonary fibrosis in mice

Cigarette smoke (CS) is a risk factor for pulmonary fibrosis and lipopolysaccharides (LPS) are associated with human occupational lung diseases; however, their combined role in pulmonary fibrosis remains unknown. Therefore, we investigated whether CS combined with LPS induces pulmonary fibrosis in mice. C57BL/6 mice were exposed to CS or normal air for 21 or 35 days, followed by LPS or saline instillation on day 14, 21, and 28. Lung function was tested, and lung tissues were harvested for histological and molecular analyses. Compared to the control, CS and LPS groups, the CS + LPS group showed reduced body weight and survival rate, increased respiratory resistance, decreased lung compliance, marked alveolar structure destruction, and fibrotic lesion formation. Lung tissues showed a considerable increase in IL-6, TNF-α, IL-1β, α-SMA, and TGF-β levels and collagen content. Our results indicate that cigarette smoke exposure followed by LPS in mice induces pulmonary fibrosis with pathophysiology consistent with that of human pulmonary fibrosis.

Chronic microaspiration of bile acids induces lung fibrosis through multiple mechanisms in rats.

Gastroesophageal reflux (GER) and microaspiration of duodenogastric refluxate have been recognized as a risk factor for pulmonary fibrosis. Recent evidence suggests that bile acid microaspiration may contribute to the development of lung fibrosis. However, the molecular evidence is scarce and the underlying mechanisms remain to be elucidated. We have recently demonstrated that bile acids induce activation of alveolar epithelial cells (AECs) and lung fibroblasts invitro In the present study, a rat model of bile acid microaspiration was established by weekly intratracheal instillation of three major bile acids including chenodeoxycholic acid (CDCA), deoxycholic acid (DCA), and lithocholic acid (LCA). Repeated microaspiration of CDCA, DCA, and LCA caused fibrotic changes, including alveolar wall thickening and extensive collagen deposition, in rat lungs. Bile acid microaspiration also induced alveolar epithelial-mesenchymal transition (EMT), as indicated by up-regulation of mesenchymal markers α-smooth muscle actin (α-SMA) and vimentin, as well as down-regulaton of epithelial markers E-cadherin and cytokeratin in alveolar epithelium of rat lungs. The expression of fibrogenic mediators, including transforming growth factor-β1 (TGF-β1), connective tissue growth factor (CTGF), basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), and periostin, was significantly elevated in rat lungs exposed to microaspiration of bile acids. Furthermore, microaspiration of bile acids also induced p-Smad3 and farnesoid X receptor (FXR) expression in rat lungs. Our findings suggest that microaspiration of bile acids could promote the development of pulmonary fibrosis invivo, possibly via stimulating fibrogenic mediator expression and activating TGF-β1/Smad3 signaling and FXR.

Risk factors for pulmonary fibrosis in patients with paraquat poisoning

Objective: To investigate the risk factors for pulmonary fibrosis in patients with paraquat (PQ) poisoning. Methods: A total of 120 patients with PQ poisoning who were admitted from January 2012 to December 2014 were enrolled. According to the presence or absence of pulmonary fibrosis, the patients were divided into non-pulmonary fibrosis group (67 patients) and pulmonary fibrosis group (53 patients) . The Acute Physiology and Chronic Health Evaluation II (APACHE II) score was obtained on days 1 and 3 of poisoning. Routine blood test results, blood biochemical parameters, and radiological parameters were recorded, and the patients with PQ poisoning were followed up for survival and pulmonary fibrosis. Results: A total of 39 patients with PQ poisoning died, resulting in a mortality rate of 32.5%. There were 53 patients who developed pulmonary interstitial fibrosis, yielding an incidence rate of 44.2%. Compared with the non-pulmonary fibrosis group, the pulmonary fibrosis group had a significantly higher age, a significantly higher dose of PQ, and significantly higher APACHE II scores on days 1 and 3 of poisoning (P<0.01) , as well as significantly higher white blood cell (WBC) count and neutrophil count on day 1, significantly higher levels of urea nitrogen, creatinine, and blood glucose on days 1 and 3, and significantly higher activities of aspartate aminotransferase (AST) and alanine aminotransferase (ALT) (P<0.01) . The logistic regression analysis showed that the dose of PQ, WBC count and neutrophil count on day 1, APACHE II scores on days 1 and 3 of poisoning, levels of urea nitrogen, creatinine, and blood glucose, and activities of AST and ALT were associated with the development of pulmonary fibrosis in patients with PQ poisoning. Conclusion: Oral dose of PQ, APACHE II scores on days 1 and 3 of poisoning, levels of urea nitrogen, creatinine, and blood glucose, activities of AST and ALT, and WBC count and neutrophil count on day 1 are risk factors for pulmonary fibrosis in patients with paraquat poisoning.

Lung damage induced by hyperglycemia in diabetic rats: The role of signal transducer and activator of transcription 3 (STAT3)

Increased evidence has shown that diabetes can be a risk factor for pulmonary fibrosis. The objective of this study was to use streptozotocin-induced diabetic rats (STZ rats) to assess the possible signals associated with lung damage in diabetic disorders. The expression levels of signal transducer and activator of transcription 3 (STAT3) and connective tissue growth factor (CTGF) in lung tissues were measured through Western blot analysis and real-time PCR. Additionally, the potential mechanisms were confirmed in cultured rat lung cell line (L2) incubated in high-glucose (HG) medium to mimic the in vivo changes. The pathological changes in the lung tissues of STZ rats were characterized using the bleomycin-treated tissues as reference. Moreover, the higher expression levels of STAT3 and CTGF in the lung tissues of STZ rats were reversed by treating the hyperglycemia. CTGF expression increased following the higher expression of STAT3 in the cultured L2 cells exposed to HG, and this change was reversed by siRNA treatment specific for STAT3. Stattic, at a dose sufficient to inhibit STAT3, reduced the CTGF levels in the lungs of STZ rats. In conclusion, STAT3 enhanced CTGF expression in a type-1 diabetes model associated with lung damage. Thus, STAT3 inhibitors may be developed to improve diabetes-induced lung damage in the future.

Type 1 diabetes mellitus is an independent risk factor for pulmonary fibrosis.

The objective of this study was to assess the clinical and histopathological relationship between pulmonary fibrosis and type 1 diabetes. We examined clinical pulmonary function parameters and transbronchial lung biopsies to assess associated histopathological changes in 12 type 1 diabetic patients presenting with dyspnea. Lung CT images pulmonary function tests from 12 diabetic patients without dyspnea and from 12 matched normal subjects served as controls. A similar histopathological analysis, including cytokine levels and pro-fibrotic markers, was performed on lung tissues in mice after the induction of experimental diabetes in an attempt to strengthen the link between diabetes and pulmonary fibrosis. Pulmonary function parameters (FVC, FEV1, TLC, and DLco/VA) were significantly reduced in diabetic patients with dyspnea and without dyspnea, compared to controls. Both patient groups also had increased lung CT scores and symptoms compared to normal controls, though the greatest increases were in the diabetic patients with dyspnea. Chronic hyperglycemia induced in mice led to histopathological changes in the lungs that were similar to those found in the human diabetic subjects and included alveoli compression by hyperplastic interstitium infiltrated with inflammatory cells and fibrotic in nature. Two inflammatory related genes, TNF-α and PAI-1, and two fibrosis-related genes, CTGF and fibronectin, demonstrated increased mRNA and protein expression in diabetic mouse lungs. In conclusion, there were significant clinical and histopathological correlations between pulmonary fibrosis and the presence of type 1 diabetes. Diabetes was clinically associated with pulmonary fibrosis and dysfunction in humans, and diabetes induction led to a similar pulmonary fibrosis in an experimental model. These clinical and non-clinical data suggest that diabetes is an independent risk factor for pulmonary fibrosis.

Interstitial lung disease in connective tissue diseases: evolving concepts of pathogenesis and management.

Interstitial lung disease (ILD) is a challenging clinical entity associated with multiple connective tissue diseases, and is a significant cause of morbidity and mortality. Effective therapies for connective tissue disease-associated interstitial lung disease (CTD-ILD) are still lacking. Multidisciplinary clinics dedicated to the early diagnosis and improved management of patients with CTD-ILD are now being established. There is rapid progress in understanding and identifying the effector cells, the proinflammatory and profibrotic mediators, and the pathways involved in the pathogenesis of CTD-ILD. Serum biomarkers may provide new insights as risk factors for pulmonary fibrosis and as measures of disease progression. Despite these recent advances, the management of patients with CTD-ILD remains suboptimal. Further studies are therefore urgently needed to better understand these conditions, and to develop effective therapeutic interventions.

HLA associations in three mutually exclusive autoantibody subgroups in UK systemic sclerosis patients.

Systemic sclerosis (SSc) is characterized by the presence of autoantibodies, mostly IgG, which target a limited set of nuclear proteins. These antinuclear antibodies (ANA) associate with disease subgroups and specific organ involvement. Here we show that there is mutual exclusivity of individual ANA in 130 UK SSc patients, confirm clinical associations with antibody profile and extend the analysis to include genetic data. The ANA mutual exclusivity observed leads to the possibility that SSc, in these patients, is in fact three separate diseases. An alternative explanation for exclusivity relates to the fact that optimal production of IgG antibody requires T-cell help, a process restricted by the HLA class II presentation of antigen peptide. If each autoantibody has a different and tight MHC restriction, then there is a possibility that these groups arose from a common pathway and were modified by genetics into the mutually exclusive groups observed, making the separate disease theory less tenable. In order to answer this question, we have determined MHC class II restriction precisely using high-resolution HLA genotyping (SSP) coupled with an amino acid analysis program in our 130 UK SSc patients. DRB1*11 was associated with anti-topoisomerase-I antibody (ATA)-positive patients (P = 0.007) and when combined with ATA (RR = 15.82), dcSSc (RR = 11.45), or both (RR = 21.9), represented the strongest risk factor for pulmonary fibrosis. Patients with antibodies to RNA polymerases I, II and III were associated with DQB1*0201. At the amino acid level, 20 positions in DRB1 and 20 positions in DQB1 showed some significant correlation with an ANA group. Clearly, however, the linkages to MHC class II alleles are not nearly strong enough to explain the mutually exclusive nature of the autoantibody groups and our results support, but do not prove, the separate disease theory.