Are anti-ribosomal P protein antibodies relevant in systemic lupus erythematosus?

Lupus Hepatitis: A Rare Manifestation Revealing Systemic Lupus Erythematosus

Systemic lupus erythematosus (SLE) is a rare disease in children but is more severe than in adults. SLE may be associated with various non-specific hepatic manifestations, but subacute lupus hepatitis remains unusual and is rarely a mode of revelation. Diagnosis is based on a combination of clinical, laboratory, and histological findings after ruling out other causes of hepatitis, notably autoimmune hepatitis (AIH). We report the case of a young girl with undiagnosed SLE, which first revealed itself as liver involvement and progressed well on corticosteroid therapy. During the course of her illness, she presented with other manifestations that led us to think of SLE with lupus hepatitis.

Serological and clinical associations of autoantibodies in Chinese patients with new-onset systemic lupus erythematosus

To study the clinical significance of autoantibodies in Chinese patients with new-onset systemic lupus erythematosus (SLE), we enrolled 526 new-onset patients who met the 1997 Updated American College of Rheumatology SLE Classification Criteria for a retrospective cohort study. Chi-square test and Wilcoxon rank-sum test were used to detect the relationship of autoantibodies with clinical manifestations and serological results respectively. Our results demonstrated that the positive rate of anti-ribosomal P protein (anti-P) antibody in female patients was higher than that in male patients (41.2% vs. 22%, P = 0.008). Patients with anti-SSB (43.95 ± 73.12 vs. 40.92 ± 75.75, P = 0.004; 63.93 ± 103.56 vs. 55.06 ± 120.84, P = 0.008 respectively) antibodies had higher levels of alanine aminotransferase (ALT) and aspartate transaminase (AST), whereas those with anti-P antibody (28.90 ± 25.70 vs. 50.08 ± 93.00, P = 0.014; 38.51 ± 48.19 vs. 69.95 ± 142.67, P = 0.047, respectively) had lower levels of them. Anti-dsDNA antibody (P = 0.021) was associated with pulmonary arterial hypertension (PAH). The patients with anti-Ro60 (P = 0.044), anti-P (P = 0.012) and anti-dsDNA (P = 0.013) antibodies were less likely to develop Interstitial lung disease. Anti-SmRNP antibody was correlated to lower prevalence of neuropsychiatric symptoms (P = 0.037), and patients with anti-centromere antibody (ACA) were more likely to develop serositis (P = 0.016).We identified five clusters of SLE-related autoantibodies, confirmed previously reported associations of autoantibodies, and discovered new associations.

The diagnostic benefit of antibodies against ribosomal proteins in systemic lupus erythematosus

BACKGROUND

Anti-ribosomal P (anti-Rib-P) antibody is a specific serological marker for systemic lupus erythematosus (SLE) and routinely tested by targeting the common epitope of three ribosomal proteins of P0, P1 and P2. This study aimed to investigate if testing antibodies against individual ribosomal protein, but not the common epitope, is required to achieve the best diagnostic benefit in SLE.

METHODS

The study included 82 patients with SLE and 22 healthy donors. Serum antibodies were determined by ELISA and immunoblot.

RESULTS

The prevalence of each antibody determined by ELISA was 35.4% (anti-Rib-P), 45.1% (anti-Rib-P0), 32.9% (anti-Rib-P1) and 40.2% (anti-Rib-P2) at 99% specificity, respectively. Of 53 patients with negative anti-Rib-P antibody, 21 (39.6%) were positive for anti-Rib-P0, 9 (17.0%) for anti-Rib-P1 and 12 (22.6%) for anti-Rib-P2 antibody. The positive rate of anti-Rib-P antibody detected by ELISA was close to the results by immunoblot (33.4%). Patients with any of these antibodies were featured by higher disease activity and prevalence of skin rashes than those with negative antibodies. Moreover, each antibody was particularly related to some clinical and laboratory disorders. The distribution of subclasses of IgG1-4 was varied with each antibody. Anti-Rib-P0 IgG1 and IgG3 were strongly correlated with disease activity and lower serum complement components 3 and 4.

CONCLUSIONS

Anti-Rib-P antibody is not adequate to predict the existence of antibodies against ribosomal P0, P1 and P2 protein. The examination of antibodies against each ribosomal protein is required to achieve additional diagnostic benefit and to evaluate the association with clinical and serological disorders as well.

Study on the correlation between anti-ribosomal P protein antibody and systemic lupus erythematosus

The aims of this study were to compare diagnostic value of anti-ribosomal P protein antibody (anti-P), anti-Smith antibody (anti-Sm), anti-double-stranded DNA antibody (anti-dsDNA), anti-nucleosome antibody (ANuA), and anti-histone antibody (AHA) for systemic lupus erythematosus (SLE) as well as explore the correlation between anti-P and SLE.A retrospective study was performed with 487 SLE patients, 235 non-SLE rheumatic diseases, and 124 healthy subjects from January 2015 to December 2018. Clinical manifestations, laboratory results and Systemic Lupus Erythematosus Disease Activity Index (SLEDAI)-2000 scores were analyzed between anti-P/+/ and anti-P/-/ patients. SPSS19.0 statistical software was used for data analysis.The sensitivities of anti-P, anti-Sm, anti-dsDNA, ANuA, and AHA in SLE were 31.6%, 20.7%, 45.0%, 27.9%, and 14.6%, and the specificities were 99.2%, 99.4%, 98.9%, 98.3%, and 96.7%, respectively. Only 27.9% of SLE had a single positive anti-P while the other 4 antibodies were all negative. There were significant differences in the age of onset, skin erythema, urinary protein, creatinine and serum IgG, IgM, C3, C4 between anti-P/+/ and anti-P/-/ patients (P < .05). When anti-Sjogren syndrome A antibody, anti-P were positive and anti-dsDNA was negative, the incidence of skin erythema was the highest (35.1%). Compared with anti-P/-/ patients, anti-P/+/ patients had higher SLEDAI scores (P < .001).Anti-P, anti-Sm, anti-dsDNA, ANuA, and AHA have high specificity but poor sensitivity in the diagnosis of SLE; combined detection can greatly improve the detection rate. Anti-P is more valuable in the diagnosis of SLE when other specific autoantibodies are negative. SLE patients with positive anti-P have an earlier onset age and are more prone to skin erythema, lupus nephritis as well as higher disease activity.

Diagnostic approach to neuropsychiatric lupus erythematosus: what should we do?

Neuropsychiatric systemic lupus erythematosus is a diagnostic challenge due to the multifarious neurological and psychiatric manifestations that define it but, when suspected, diagnostic imaging can give a fundamental help. The advancements and variety of neuroimaging techniques allow us to perform more and more accurate evaluations of structure, perfusion, and metabolism of the brain and to detect cerebral and spinal lesions. Moreover, vascular districts of the neck and the brain, as well as the electrical brain and peripheral muscle activity may be accurately investigated, thus giving us a wide panoramic view. Although magnetic resonance is recognized as a fundamental neuroimaging technique to reach a correct diagnosis, the juxtaposition of other diagnostic techniques has improved the possibility to make diagnoses but has also increased the confusion about deciding which of them to use and when. Our aim was to combine the number of available techniques with the need to simplify the diagnostic path. Therefore, through the construction of an algorithm from an evidence based approach, we believe we are providing some added improvements to facilitate and expedite the diagnosis of NPSLE.

Autoantibodies in SLE: Specificities, Isotypes and Receptors

Systemic Lupus Erythematosus (SLE) is characterized by a wide spectrum of auto-antibodies which recognize several cellular components. The production of these self-reactive antibodies fluctuates during the course of the disease and the involvement of different antibody-secreting cell populations are considered highly relevant for the disease pathogenesis. These cells are developed and stimulated through different ways leading to the secretion of a variety of isotypes, affinities and idiotypes. Each of them has a particular mechanism of action binding to a specific antigen and recognized by distinct receptors. The effector responses triggered lead to a chronic tissue inflammation. DsDNA autoantibodies are the most studied as well as the first in being characterized for its pathogenic role in Lupus nephritis. However, others are of growing interest since they have been associated with other organ-specific damage, such as anti-NMDAR antibodies in neuropsychiatric clinical manifestations or anti-β2GP1 antibodies in vascular symptomatology. In this review, we describe the different auto-antibodies reported to be involved in SLE. How autoantibody isotypes and affinity-binding to their antigen might result in different pathogenic responses is also discussed.

A meta-analysis of serum and cerebrospinal fluid autoantibodies in neuropsychiatric systemic lupus erythematosus

Neuropsychiatric systemic lupus erythematosus (NPSLE) is one of the most devastating presentations of SLE and comprises of psychiatric, central and peripheral neurological signs and symptoms. Previous studies suggest the possible associations between various autoantibodies (Abs) and NPSLE. The magnitudes of such association varied between studies. We performed a meta-analysis to pool data on serum and cerebrospinal fluid (CSF) levels and positivity of Abs in blood and cerebrospinal fluid in patients with NPSLE and SLE. A systematic literature search was conducted to identify studies that fulfilled inclusion criteria. A random-effects model was used to calculate overall combined odd ratio (OR) and mean levels with its corresponding 95% confidence interval to evaluate the relationship between individual Abs and NPSLE patients relative to SLE patients. Forty-one studies met the inclusion criteria and were used in this analysis. There was a significantly greater proportion of NPSLE patients who demonstrated positivity for serum anti-cardiolipin (aCL) Abs (OR=1.63, p=0.016), lupus anticoagulants (LA) Abs (OR=1.91 p=0.01), anti-phospholipid (APL) Abs (OR=2.08, p=0.001), anti-ribosomal P Abs (OR=2.29, p<0.001), anti-neuronal Abs (OR=9.50, p<0.001) as compared to SLE patients. In NPSLE patients, there was a significant increased prevalence of positive titres for CSF anti-neuronal Abs (OR=36.84, p=0.001) as compared to SLE patients. Among the 19 neuropsychiatric syndromes, the positivity of these serum autoantibodies were found specifically significantly associated with the manifestations of mood disorder, psychosis, cerebrovascular disease, seizure disorders, acute confusional state, cognitive dysfunction, headache, movement disorder, demyelinating syndrome and polyneuropathy, with ORs ranging from 1.84 to 4.73. Meta-regression identified proportion of women as significant moderator for the heterogeneity of aCL (p=0.004) and anti-neuronal Abs (p=0.0007); mean age for the heterogeneity of aCL (p=0.042) and LA (p=0.020) Abs, mean duration of illness for the heterogeneity of aCL Abs (p=0.035), and mean SLEDAI scores for the heterogeneity of anti-ribosomal P Abs (p=0.014). NPSLE patients are more likely to have elevated serum levels of aCL, LA, APL, anti-ribosomal P Abs and anti-neuronal Abs compared with SLE patients. Further research is required to evaluate the accuracy of using the above antibodies as an adjunct diagnostic tool in NPSLE.

Autoantibody profiling on human proteome microarray for biomarker discovery in cerebrospinal fluid and sera of neuropsychiatric lupus

Autoantibodies in cerebrospinal fluid (CSF) from patients with neuropsychiatric systemic lupus erythematosus (NPSLE) may be potential biomarkers for prediction, diagnosis, or prognosis of NPSLE. We used a human proteome microarray with~17,000 unique full-length human proteins to investigate autoantibodies associated with NPSLE. Twenty-nine CSF specimens from 12 NPSLE, 7 non-NPSLE, and 10 control (non-systemic lupus erythematosus)patients were screened for NPSLE-associated autoantibodies with proteome microarrays. A focused autoantigen microarray of candidate NPSLE autoantigens was applied to profile a larger cohort of CSF with patient-matched sera. We identified 137 autoantigens associated with NPSLE. Ingenuity Pathway Analysis revealed that these autoantigens were enriched for functions involved in neurological diseases (score = 43).Anti-proliferating cell nuclear antigen (PCNA) was found in the CSF of NPSLE and non-NPSLE patients. The positive rates of 4 autoantibodies in CSF specimens were significantly different between the SLE (i.e., NPSLE and non-NPSLE) and control groups: anti-ribosomal protein RPLP0, anti-RPLP1, anti-RPLP2, and anti-TROVE2 (also known as anti-Ro/SS-A). The positive rate for anti-SS-A associated with NPSLE was higher than that for non-NPSLE (31.11% cf. 10.71%; P = 0.045).Further analysis showed that anti-SS-A in CSF specimens was related to neuropsychiatric syndromes of the central nervous system in SLE (P = 0.009). Analysis with Spearman’s rank correlation coefficient indicated that the titers of anti-RPLP2 and anti-SS-A in paired CSF and serum specimens significantly correlated. Human proteome microarrays offer a powerful platform to discover novel autoantibodies in CSF samples. Anti-SS-A autoantibodies may be potential CSF markers for NPSLE.

Anti-ribosomal P protein: a novel antibody in autoimmune hepatitis

BACKGROUND

Autoantibodies to ribosomal P proteins (anti-rib P) are specific serological markers for systemic lupus erythematosus (SLE) and are associated with liver involvement in this disease. The similarity in autoimmune background between autoimmune hepatitis (AIH) and SLE-associated hepatitis raises the possibility that anti-rib P antibodies might also have relevance in AIH.

AIMS

To evaluate the frequency and clinical significance of anti-rib P antibodies in a large AIH cohort.

METHODS

Sera obtained at diagnosis of 96 AIH patients and of 82 healthy controls were tested for IgG anti-ribosomal P protein by ELISA. All of the sera were also screened for other lupus-specific autoantibodies, three patients with the presence of anti-dsDNA (n = 1) and anti-Sm (n = 2) were excluded.

RESULTS

Moderate to high titres (>40 U) of anti-rib P antibody were found in 9.7% (9/93) of the AIH patients and none of the controls (P = 0.003). At presentation, AIH patients with and without anti-rib P antibodies had similar demographic/clinical features, including the frequency of cirrhosis (44.4 vs. 28.5%, P = 0.44), hepatic laboratorial findings (P > 0.05). Importantly, at the final observation (follow-up period 10.2 ± 4.9 years), the AIH patients with anti-rib P had a significantly higher frequency of cirrhosis compared with the negative group (100 vs. 60%, P = 0.04).

CONCLUSION

The novel demonstration of anti-rib P in AIH patients without clinical or laboratory evidence of SLE suggests a common underlying mechanism targeting the liver in these two diseases. In addition, this antibody appears to predict the patients with worse AIH prognoses.

Clinical and immunological features of 888 Brazilian systemic lupus patients from a monocentric cohort: comparison with other populations

Epidemiological studies with systemic lupus erythematosus (SLE) patients have been reported worldwide but, until now, a large evaluation had not been performed in Brazil. Therefore, we determined the clinical and immunological features of 888 SLE patients followed at our service from 2008 to 2012. The mean age at SLE onset and the mean disease duration were 29.9 ± 9.5 years old and 14.5 ± 8.4 years, respectively. A predominance of female gender (91.9%) and Caucasian ethnicity (69.9%) were observed. Cumulative mucocutaneous manifestations (90.7%) were most commonly identified (malar rash (83.2%), photosensitivity (76.9%)) followed by articular (87.4%), hematological (44.0%) and renal (36.9%) involvements. Antinuclear antibody was detected in all patients, followed by anti-dsDNA (35.1%), anti-Sm (21.8%) and anti-ribosomal P protein antibodies (19.8%). Additional comparison of clinical and laboratory features between genders revealed that malar rash was observed more in female SLE patients (84.5% vs. 69.4%, p = 0.001). Male lupus patients presented a higher frequency of anti-dsDNA (45.8% vs. 34.2%, p = 0.047) and a trend of more nephritis (47.2% vs. 36.0%, p = 0.059). In conclusion, we identified a high prevalence of mucocutaneous manifestations in this Brazilian SLE cohort compared to other countries, mainly malar rash that was most commonly observed in female patients. Anti-dsDNA and other specific SLE autoantibodies were also identified in a higher frequency, predominantly in the male gender.

Significance of antibodies against the native ribosomal P protein complex and recombinant P0, P1, and P2 proteins in the diagnosis of Chinese patients with systemic lupus erythematosus

BACKGROUND

This study aimed to evaluate autoantibodies against the native ribosomal P complex (anti-Rib-P(C)) and recombinant ribosomal P proteins (anti-Rib-P0, anti-Rib-P1, anti-Rib-P2) for their prevalence, diagnostic relevance and clinical associations in a Chinese cohort with systemic lupus erythematosus (SLE).

METHODS

Anti-Rib-P, anti-dsDNA and anti-Smith antigen (Sm) antibodies were analyzed in sera from 198 patients with SLE, 33 with rheumatoid arthritis, 61 with Sjögren's syndrome and 70 healthy individuals by means of ELISA.

RESULTS

Antibody prevalences were 29.8% (anti-Rib-P(C)), 33.3% (anti-Rib-P0), 42.9% (anti-Rib-P1) and 34.3% (anti-Rib-P2), at a specificity of 99%. Among SLE patients lacking anti-dsDNA and anti-Sm, 27.8% showed positive for at least one of the investigated anti-Rib-P types. The serological hit rate provided by anti-dsDNA/anti-Sm detection (72.7%) was increased upon parallel testing for anti-Rib-P(C) (77.3%) or anti-Rib-P0/P1/P2 (80.3%). Anti-Rib-P positivity was associated with disease activity, neuropsychiatric events, lupus nephritis, skin rash, lymphocytopenia, increased erythrocyte sedimentation rates, decreased complement C3/C4 and elevated IgA/IgG levels.

CONCLUSION

Based on these results, antibodies against ribosomal P proteins are important complementary parameters to anti-dsDNA and anti-Sm, and should be considered for inclusion in the classification criteria for SLE. The diagnostic value of anti-Rib-P0/P1/P2 is diagnostically superior to that of anti-Rib-P(C).

Neuropsychiatric lupus: clinical challenges, brain-reactive autoantibodies and treatment strategies

Neurological manifestations in lupus can be due to active lupus disease affecting the brain or to other reasons. Reversible posterior leucoencephalopathy syndrome, primary lymphoma of the central nervous system, cerebral infections by bacteria (e.g. mycobacteria), viruses (e.g. JC virus), fungi (e.g. Cryptococcus) and parasites (e.g. Acanthamoeba), steroid-induced psychosis and reactive depression need to be excluded. Brain-reactive autoantibodies have been described as associating with neuropsychiatric lupus. The strongest associations described to date are with antiribosomal P protein and antiphospholipid antibodies. However these autoantibodies have not been shown to play significant roles in the pathogenesis. Treatment strategy for severe neuropsychiatric lupus include establishing definitive diagnosis, early identification and treatment of aggravating factors, appropriate symptomatic treatment, adequate immunosuppression, selective B-cell depletion and autologous haematopoietic stem cell transplant. Systematic reviews have shown that cyclophosphamide administration is superior to pulse methylprednisolone as a maintenance therapy. Mycophenolate mofetil has been shown to have modest effect and should only be considered if cyclophosphamide cannot be administered.

Diagnostic value and clinical laboratory associations of antibodies against recombinant ribosomal P0, P1 and P2 proteins and their native heterocomplex in a Caucasian cohort with systemic lupus erythematosus

Introduction

In this study, we sought to determine the diagnostic value and clinical laboratory associations of autoantibodies against recombinant ribosomal P0, P1 and P2 proteins and their native heterocomplex in systemic lupus erythematosus (SLE).

Methods

Autoantibodies against recombinant ribosomal P proteins (aRibP_R0, aRibP_R1 and aRibP_R2) and antibodies against native ribosomal P heterocomplex (aRibP_NH) were determined in sera from patients with SLE (n = 163), systemic sclerosis (n = 66), Sjögren's syndrome (n = 54), rheumatoid arthritis (n = 90) and healthy donors (n = 100) using enzyme-linked immunosorbent assay. Test results were correlated to medical records, including the American College of Rheumatology criteria, the Systemic Lupus Erythematosus Disease Activity Index 2000, laboratory data and medications of all SLE patients.

Results

Sensitivities of 22.0% for aRibP_R0, 14.9% for aRibP_R2, 14.3% for aRibP_NH and 10.7% for aRibP_R1 were obtained at a specificity of 99%. The assay for aRibP_R0 detection demonstrated the best performance in receiver-operating characteristics analysis, with aRibP_R0 detectable in 10% of anti-Smith antibody and anti-double-stranded DNA-negative sera at a specificity of 100%. ARibP_R0 positivity was associated with lymphocytopenia. ARibP_R1⁺ patients had significantly higher γ-glutamyl transpeptidase (GGT) levels than their aRibP_R1^- counterparts. No specific damage occurred in aRibP⁺ lupus patients compared with a group of age-, sex- and nephritis-matched aRibP^- lupus patients within 3 years.

Conclusions

The determination of antibodies against ribosomal P proteins improves the diagnosis of SLE and should therefore be implemented in upcoming criteria for the diagnosis or classification of SLE. High titers of aRibP_R0 can be associated with lymphocytopenia, and high titers of aRibP_R1 can be associated with elevated GGT levels. So far, there is no evidence for a prognostic value of aRibPs for damage.

[Lupus hepatitis: a case series of 12 patients]

PURPOSE

Several liver manifestations have been reported in systemic lupus erythematosus (SLE) and are usually non specific. We report on our experience of lupus hepatitis.

METHODS

A retrospective monocenter study of 73 patients with SLE. The diagnosis of lupus hepatitis was established after exclusion of other causes of hepatitis and hepatic vein thrombosis.

RESULTS

Liver involvement was noted in 12 patients (16.4%). There were nine female and three male patients; the mean age of these patients was 29 years. In seven patients liver involvement was concurrent with the diagnosis of SLE and it occurred later during an exacerbation of the disease in the five remaining patients. In all patients, liver manifestations were associated with other organ involvement. Clinical manifestations were: hepatomegaly (n=4), jaundice (n=4), abdominal pain (n=3), ascites (n=2), portal hypertension (n=1) and hepatic failure with encephalopathy (n=1). Elevated liver enzyme was noted in 11 cases and liver cholestasis in eight cases. Presence of anti-ribosomal P antibodies was noted in one case. Liver biopsy was performed in five patients, and revealed chronic active hepatitis in three cases, chronic hepatic granulomas in one case and nonspecific inflammation in one case. The outcome was favorable in 11 patients without relapse, and one patient died of encephalopathy and liver failure.

CONCLUSION

Liver involvement associated with SLE is not uncommon. It is frequently asymptomatic and limited to liver test abnormalities. The role of anti-ribosomal P autoantibodies remains uncertain.

How common are extraribosomal functions of ribosomal proteins?

Ribosomal proteins are ubiquitous, abundant, and RNA binding: prime candidates for recruitment to extraribosomal functions. Indeed, they participate in balancing the synthesis of the RNA and protein components of the ribosome itself. An exciting new story is that ribosomal proteins are sentinels for the self-evaluation of cellular health. Perturbation of ribosome synthesis frees ribosomal proteins to interface with the p53 system, leading to cell-cycle arrest or to apoptosis. Yet in only a few cases can we clearly identify the recruitment of ribosomal proteins for other extraribosomal functions. Is this due to a lack of imaginative evolution by cells and viruses, or to a lack of imaginative experiments by molecular biologists?

Autoantibodies involved in neuropsychiatric manifestations associated with systemic lupus erythematosus

In the course of Systemic Lupus Erythematosus (SLE), a variety of neuropsychiatric disturbances is reported with a prevalence ranging from 17% to 75%. The diagnosis of these syndromes is difficult and requires a careful psychiatric evaluation. Distinct autoantibodies detectable in serum or cerebrospinal fluid of patients with SLE are associated with the presence of neuropsychiatric disorders. These autoantibodies may have a pathogenic relevance in neuropsychiatric SLE or they may be merely an epiphenomenon. This review describes the various autoantibodies reported to be associated with neuropsychiatric manifestations in SLE and discusses their possible role.

Autoimmune pathology accounts for common manifestations in a wide range of neuro-psychiatric disorders: the olfactory and immune system interrelationship

Smell has traditionally been considered a less important sense when compared to sight or hearing, but recent research has unraveled important features inherent to the sense of smell. Once considered just a chemical sensor for sampling the environment, data from animal models and human studies currently imply numerous and complex effects of smell on behavior, mood, and on the immune response. In this review we discuss a possible inter-relationship between olfactory impairment, autoimmunity and neurological/psychiatric symptoms in several diseases affecting the central nervous system (CNS) such as Parkinson, Alzheimer's disease, autism, schizophrenia, multiple sclerosis and neuropsychiatric lupus erythematosus. We suggest that common manifestations are not mere coincidences. Current data from animal models show that neuropsychiatric manifestations are intimately associated with smell impairment, and autoimmune dysregulation, via autoantibodies (anti-NMDAR, anti-ribosomal P) or other mechanisms. From clues of pathological manifestations, we propose a novel approach to the understanding of the interactions between the CNS, the smell and the immune system.

Limited reliability of the indirect immunofluorescence technique for the detection of anti-Rib-P antibodies

Introduction

Autoantibodies to the ribosomal P proteins represent a highly specific marker for the diagnosis of systemic lupus erythematosus, where they have been associated with certain clinical manifestations. Historically, autoantibodies against ribosomal P proteins have been detected by indirect immunofluorescence, immunodiffusion, immunoblot, and other immunoassays. More recently, enzyme-linked immunosorbent assays and line and addressable laser bead immunoassays have become more widely used. The primary goal of this study was to determine the sensitivity of indirect immunofluorescence using conventional HEp-2 substrates in the detection of sera with ribosomal P antibodies as detected by other immunoassays.

Methods

Anti-ribosomal P-positive sera (n = 345) as detected by an addressable laser bead immunoassay were collected between 2003 and 2007 and analysed by indirect immunofluorescence. Furthermore, 51 anti-ribosomal P-positive samples from an unselected systemic lupus erythematosus cohort (n = 100) and the Centers for Disease Control and Prevention (CDC) anti-nuclear antibody (ANA) reference sera were tested for anti-ribosomal P reactivity.

Results

In the cohort of 345 anti-ribosomal P-positive samples identified by addressable laser bead immunoassay, a low sensitivity (<30%) of indirect immunofluorescence on HEp-2 cell substrates was observed. Although the degree of sensitivity varied among different manufacturers, all immunofluorescence substrates exhibited limited sensitivity and false-negative results were not restricted to samples with low anti-ribosomal P titers. Even the anti-ribosomal P reactivity of CDC ANA reference serum number 12 was not clearly predictable by indirect immunofluorescence. Comparison of five different methods for the detection of anti-ribosomal P found moderate qualitative agreements.

Conclusions

Based on our data, we conclude that indirect immunofluorescence on HEp-2 cells is not a reliable screening test for the prediction of ribosomal P antibodies. As this method is widely used as a first-line screening test for anti-nuclear and other autoantibodies, special considerations for the detection of ribosomal P antibodies are needed. As with many other autoantibodies, further effort is required for the standardisation of ribosomal P immunoassays.

Mapping the genetic architecture of gene expression in human liver

Genetic variants that are associated with common human diseases do not lead directly to disease, but instead act on intermediate, molecular phenotypes that in turn induce changes in higher-order disease traits. Therefore, identifying the molecular phenotypes that vary in response to changes in DNA and that also associate with changes in disease traits has the potential to provide the functional information required to not only identify and validate the susceptibility genes that are directly affected by changes in DNA, but also to understand the molecular networks in which such genes operate and how changes in these networks lead to changes in disease traits. Toward that end, we profiled more than 39,000 transcripts and we genotyped 782,476 unique single nucleotide polymorphisms (SNPs) in more than 400 human liver samples to characterize the genetic architecture of gene expression in the human liver, a metabolically active tissue that is important in a number of common human diseases, including obesity, diabetes, and atherosclerosis. This genome-wide association study of gene expression resulted in the detection of more than 6,000 associations between SNP genotypes and liver gene expression traits, where many of the corresponding genes identified have already been implicated in a number of human diseases. The utility of these data for elucidating the causes of common human diseases is demonstrated by integrating them with genotypic and expression data from other human and mouse populations. This provides much-needed functional support for the candidate susceptibility genes being identified at a growing number of genetic loci that have been identified as key drivers of disease from genome-wide association studies of disease. By using an integrative genomics approach, we highlight how the gene RPS26 and not ERBB3 is supported by our data as the most likely susceptibility gene for a novel type 1 diabetes locus recently identified in a large-scale, genome-wide association study. We also identify SORT1 and CELSR2 as candidate susceptibility genes for a locus recently associated with coronary artery disease and plasma low-density lipoprotein cholesterol levels in the process.

Genome-wide association studies seek to identify regions of the genome in which changes in DNA in a given population are correlated with disease, drug response, or other phenotypes of interest. However, changes in DNA that associate with traits like common human diseases do not lead directly to disease, but instead act on intermediate, molecular phenotypes that in turn induce changes in the higher-order disease traits. Therefore, identifying molecular phenotypes that vary in response to changes in DNA that also associate with changes in disease traits can provide the functional information necessary to not only identify and validate the susceptibility genes directly affected by changes in DNA, but to understand as well the molecular networks in which such genes operate and how changes in these networks lead to changes in disease traits. To enable this type of approach we profiled the expression levels of 39,280 transcripts and genotyped 782,476 SNPs in 427 human liver samples, identifying thousands of DNA variants that strongly associated with liver gene expression. These relationships were then leveraged by integrating them with genotypic and expression data from other human and mouse populations, leading to the direct identification of candidate susceptibility genes corresponding to genetic loci identified as key drivers of disease. Our analysis is able to provide much needed functional support for these candidate susceptibility genes.

Identifying changes in DNA that associate with changes in gene expression in human tissues elucidates the genetic architecture of gene expression in human populations and enables the direct identification of functionally supported candidate susceptibility genes in genomic regions associated with disease.