Evaluation of assays for the detection of autoantibodies to the ribosomal P proteins

Cloning and molecular characterization of telomerase reverse transcriptase (TERT) and telomere length analysis of Peromyscus leucopus

Telomerase reverse transcriptase (TERT) is the catalytic subunit of telomerase complex that regulates telomerase activity to maintain telomere length for all animals with linear chromosomes. As the Mus musculus (MM) laboratory mouse has very long telomeres compared to humans, a potential alternative animal model for telomere research is the Peromyscus leucopus (PL) mouse that has telomere lengths close to the human range and has the wild counterparts for comparison. We report the full TERT coding sequence (pTERT) from PL mice to use in the telomere research. Comparative analysis with eight other mammalian TERTs revealed a pTERT protein considerably homologous to other TERTs and preserved all TERT specific-sequence signatures, yet with some distinctive features. pTERT displayed the highest nucleotide and amino acid sequence homology with hamster TERT. Unlike human but similar to MM mice, pTERT expression was detected in various adult somatic tissues of PL mice, with the highest expression in testes. Four different captive stocks of PL mice and wild-captured PL mice each displayed group-specific average telomere lengths, with the longest and shortest telomeres in inbred and outbred stock mice, respectively. pTERT showed considerable numbers of synonymous and nonsynonymous mutations. A pTERT proximal promoter region cloned was homologous among PL and MM mice and rat, but with species-specific features. From PL mice, we further cloned and characterized ribosomal protein, large, P0 (pRPLP0) to use as an internal control for various assays. Peromyscus mice have been extensively used for various studies, including human diseases, for which pTERT and pRPLP0 would be useful tools.

Expression of the ribosomal proteins Rplp0, Rplp1, and Rplp2 in gynecologic tumors

Previous work from our laboratory has demonstrated that the expression of the ribosomal protein Rplp1 immortalizes primary cells and is involved in transformation. To investigate the role of the P proteins in tumorigenesis, we examined the messenger RNA expression levels of Rplp0, Rplp1, and Rplp2 in a series of 32 patients with gynecologic tumors. The messenger RNA expression level of all 3 P proteins was increased significantly in the tumor tissue, compared with normal tissue. In addition, a total of 140 biopsies of gynecologic cancers (46 endometrioid and 94 ovarian) were investigated. An up-regulation of P protein expression was observed by immunohistochemistry in an average of 27% of the tumors, as compared with normal tissues. Moreover, the level of P protein up-regulation correlated significantly with p53 expression in serous ovarian cancers. This is an important fact because the level of overexpression of the P proteins correlated with the presence of lymph node metastases in serous ovarian cancers. We also observed that endometrial carcinomas that had invaded the myometrium overexpressed P proteins in the invasive front. In addition, we found that the P proteins are up-regulated in a considerable number of patients with the most common types of cancer. Overall, our study shows that P proteins are involved in human cancer and indicates that the expression level of these proteins could be useful as a prognostic marker in specific subtypes of gynecologic tumors.

Cerebral and cerebellar volume loss in children and adolescents with systemic lupus erythematosus: a review of clinically acquired brain magnetic resonance imaging

OBJECTIVE

Cerebral atrophy is a prominent feature in adults with systemic lupus erythematosus (SLE). We assessed cerebral and cerebellar volume loss on clinically acquired brain magnetic resonance imaging (MRI) scans of children and adolescents with SLE.

METHODS

We abstracted information on disease course for patients who underwent clinical brain MRI during the period 2002-2008. We completed qualitative assessments of volume loss and measured corpus callosum thickness and ventricular enlargement for patients with lupus and controls.

RESULTS

Forty-nine children underwent brain MRI during the review period due to clinical indications. The lupus cohort was predominantly female and ethnically diverse. Mean age at imaging was 15.3 +/- 2.6 years and mean disease duration was 30.6 +/- 33.3 months. Findings suggestive of cerebral and cerebellar volume loss were seen respectively in 89.8% and 91.8% of lupus patients. Cerebral volume loss was moderate or severe in 26.5% of children. Cerebellar volume loss was moderate in 20.4% of these patients. Linear measurement means reflected corpus callosum thinning and ventricular enlargement in lupus patients. Volume loss was observed in newly diagnosed patients prior to corticosteroid use. Disease duration and corticosteroid use did not predict the severity of volume loss. There were statistically significant differences in linear imaging measurements comparing lupus patients to 14 similar-age controls.

CONCLUSION

Regional volume loss was observed in most adolescents with lupus undergoing clinical brain MRI scans. As in other pediatric conditions with inflammatory or vascular etiologies, these findings may be reflecting disease-associated neuronal loss and not solely the effects of corticosteroid.

Neurocognitive deficits and neuroimaging abnormalities are prevalent in children with lupus: clinical and research experiences at a US pediatric institution

Neurocognitive impairments and neuroimaging abnormalities are frequently observed in adults with systemic lupus erythematosus. There is a paucity of similar data in childhood-onset disease. We hypothesized that neurocognitive and neuroimaging abnormalities would be prevalent in children undergoing neuropsychological evaluations. We reviewed patient neurocognitive evaluations performed at a large United States pediatric institution during the period 2001 to 2008. Records were retrieved from 24 children referred to neuropsychology due to clinical indications. Data from 15 children enrolled in a prospective structure-function association study were also analyzed. Subjects were predominantly African-American and Hispanic adolescent girls of average intelligence. aPL positivity and aspirin use was prevalent. Neurocognitive impairment was designated in 70.8% of retrospective, and 46.7% of prospective cohort patients. Deficits were seen at times of wellness, without previous neuropsychiatric lupus, and early in disease courses. Scores >1.5 standard deviations below published age-matched norms were common in tests of executive functioning, visual memory and visual-spatial planning. Features of depression were seen in 33.3% of the children in the retrospective cohort (clinical referrals). Cerebral and cerebellar volume loss was observed in a majority of blinded prospective cohort research magnetic resonance images (73.3% and 67.7% respectively). White matter hyperintensities were observed in retrospective and prospective cohort magnetic resonance images (36.6% and 46.7% respectively). Larger prospective studies that elucidate structure-function associations in children with systemic lupus erythematosus are planned.

International multicenter evaluation of autoantibodies to ribosomal P proteins

Autoantibodies to the ribosomal phosphoproteins (Rib-P) are a serological feature of patients with systemic lupus erythematosus (SLE). The reported prevalence of anti-Rib-P antibodies in SLE ranges from 10 to 40%, being higher in Asian patients. The variation in the observed frequency may be related to a number of factors but is dependent in large part on the test system used to detect the autoantibodies. An association of anti-Rib-P with central nervous system involvement and neuropsychiatric manifestations of SLE has been controversial. In the present international multicenter study, we evaluated the clinical accuracy of a new sensitive Rib-P-specific enzyme-linked immunosorbent assay based on recombinant Rib-P polypeptides. The results showed that 21.3% of 947 SLE patients, but only 0.7% of 1,113 control patients, had a positive test result (P < 0.0001). The sensitivity, specificity, positive and negative predictive values, and diagnostic efficiency were determined to be 21.3%, 99.3%, 95.6%, 62.2%, and 65.3%, respectively. When evaluated in the context of participating centers, the prevalence of anti-Rib-P antibodies was found in descending frequency, as follows: China (35%) > Poland (34%) > Japan (28%) > United States (26%) > Germany (Freiburg; 23.3%) > Denmark (20.5%) > Germany (Berlin; 19%) > Mexico (15.7%) > Israel (11.7%) > Brazil (10%) > Canada (8%). The substantial data from this study indicate that the prevalence of anti-Rib-P antibodies may not be restricted to the genetic background of the patients or to the detection system but may depend on regional practice differences and patient selection. We confirm previously reported associations of antiribosomal antibodies with clinical symptoms and serological findings. Remarkably, we found a lower occurrence of serositis in Rib-P-positive lupus patients.

Serological correlations with nephritis in systemic lupus erythematosus

Autoantibodies have long been thought to participate in the pathogenesis of lupus nephritis. In this regard, antibodies to double stranded (ds)DNA and ribosomal P protein have been studied the most intensively. We now report a new specificity, antibodies to lipoprotein lipase (LPL) that is strongly associated with lupus nephritis and has a powerful synergistic effect with anti-ribosomal P antibodies in its association with nephritis. The recognition of anti-LPL antibodies and their synergy with anti-P antibodies are discussed in terms of the pathogenesis of lupus nephritis.

Technical and clinical evaluation of anti-ribosomal P protein immunoassays

Autoantibodies to the three ribosomal phospho (-P) proteins P0, P1, P2, referred to as Rib-P, are specifically found in 10-40% of patients with systemic lupus erythematosus. The variations in the observed frequency of these autoantibodies is related to a number of factors such as the test system used to detect the antibodies. Several immunoassays that were designed for research and diagnostic laboratory use have been developed. The autoantigens employed in these tests include native proteins, recombinant polypeptides, and synthetic peptides. In this study, we compared the technical and clinical accuracy of anti-Rib-P antibody assays from different commercial suppliers including ELISA systems and a novel addressable laser bead assay (from Euroimmun, MBL, Pharmacia Diagnostics, INOVA). Although the assays from all suppliers used in this study performed well in the technical part of the study, relatively poor correlations and significant differences in the clinical accuracy were found. Based on the results, we conclude that the detection of anti-Rib-P antibodies strongly depends on both the nature of the antigen and the detection system. We recommend that anti-Rib-P assays should be standardized on an international level. The Varelisa Rib-P profile and the addressable laser bead Rib-P assays represent promising tools and platforms for the detection of anti-Rib-P antibodies in the future.

Accuracy of anti–ribosomal P protein antibody testing for the diagnosis of neuropsychiatric systemic lupus erythematosus: An international meta-analysis

OBJECTIVE

To quantitatively evaluate the diagnostic accuracy of antibodies to ribosomal P proteins (anti-P) for neuropsychiatric systemic lupus erythematosus (NPSLE) in general, for psychosis, mood disorder, or both, and for other diffuse manifestations.

METHODS

This international meta-analysis combined standardized data from 1,537 lupus patients contributed by 14 research teams. Weighted estimation of sensitivity and specificity with fixed-effects and random-effects models, as well as summary receiver operating characteristic (SROC) curve analysis, was used to summarize test performance. The robustness of the overall estimates was examined in sensitivity analyses that included additional studies published up to November 1, 2004 in the Medline, EMBase, and Cochrane databases.

RESULTS

Combining the data from the 14 teams, the weighted sensitivity and specificity estimates for the diagnosis of NPSLE were 26% (95% confidence interval [95% CI] 15-42%) and 80% (95% CI 74-85%), respectively. For psychosis, mood disorder, or both, the sensitivity and specificity were 27% (95% CI 14-47%) and 80% (95% CI 74-85%), respectively. For other diffuse manifestations, the sensitivity was 24% (95% CI 12-42%), and the specificity was 80% (95% CI 73-85%). The proportion of patients with anti-P antibodies did not vary markedly across different presentations of NPSLE. Between-study heterogeneity was substantial, but the SROC curves were consistent with the weighted estimates. In further analyses that included another 24 published studies, only the sensitivity for psychosis and/or mood disorder was slightly improved, but it was still suboptimal (42% [95% CI 30-53%]); the specificity remained essentially the same (81% [95% CI 76-85%]).

CONCLUSION

Anti-P antibody testing has limited diagnostic value for NPSLE, and it is not helpful in differentiating among various disease phenotypes.

The heterogeneity of neuropsychiatric systemic lupus erythematosus is reflected in lack of association with cerebrospinal fluid cytokine profiles

The objective was to study the occurrence of autoantibodies and cytokines in serum and cerebrospinal fluid (CSF) in neuropsychiatric systemic lupus erythematosus (NPSLE). In total, 28 consecutive patients with NPSLE and 16 systemic lupus erythematosus (SLE) patients without neuropsychiatric involvement (non-NPSLE) were studied. IFN-alpha, IL-6, IL-10, soluble terminal complement complex (TCC), anti-ribosomal P protein antibodies (anti-P) and anti-cardiolipin antibodies (aCL) were measured in serum and CSF by immunoassays. Analyses of white blood cell differential count, CSF-albumin/serum-albumin ratio, IgG-index in CSF and isoelectric focusing in serum and CSF were also performed. CSF specimens from 23 healthy individuals were used as controls. IFN-alpha was elevated in the CSF of 5 of 28 NPSLE patients compared to three of 14 among the non-NPSLE patients. IL-6 was elevated in CSF in three of 26 NPSLE patients. Normal concentration of IL-10 was found in CSF in all 27 NPSLE-patients analysed. IFN-alpha in serum was elevated in 18 of 28 NPSLE patients. No distinct clinical phenotype was related to elevated cytokine concentration in serum or CSF. One patient with cerebral involvement complicated by progressive multifocal leukoencephalopathy displayed a very high IFN-alpha concentration in serum. High concentration of TCC was present in CSF from only one patient with systemic vasculitis and focal cerebral symptoms. In conclusion, the results of this study suggest that the diagnostic value of serum and CSF concentrations of IFN-alpha, IL-10, IL-6 and TCC is limited in unselected neuropsychiatric SLE, probably due to the heterogeneity of NPSLE pathogenesis.

Correlations of anti-dsDNA and anti-ribosomal P autoantibodies with lupus nephritis

Patients with systemic lupus erythematosus, with and without nephritis, were studied for their serological profiles. Patients were stratified into two groups defined by the presence or the absence of precipitating antibodies to ribosomal P proteins. It was found that 27 patients were positive for anti-P precipitins and the remaining 34 patients were studied for the presence of lesser amounts of anti-P antibodies by Western blot and ELISA tests. The nephritic patients were characterized most frequently by the presence of both autoantibodies to dsDNA and the ribosomal P proteins. In the group with anti-P precipitins, anti-dsDNA titers were much higher in the patients with nephritis than in those without nephritis. Thus, over a wide range of anti-ribosomal P antibody concentrations, the mutual occurrence of anti-P antibodies with anti-dsDNA antibodies was strongly associated with lupus nephritis.

Antiribosomal P protein antibodies in Chilean SLE patients: no association with renal disease

The objective of this work was to determine the frequency and clinical associations of anti-ribosomal P protein antibodies (Anti-P) in a cohort of Chilean patients with systemic lupus erythematosus (SLE). Between 1996 and 1998, 141 consecutive patients with SLE were examined prospectively according with a standard protocol. Disease activity was measured by MEX-SLEDAI in 138 patients. Anti-P positivity was determined by double immune diffusion or Western blot and ELISA. Anti-P was found in 21 (15%) patients. In the Anti-P positive patients recent onset SLE (disease duration of 1 year or less) was more frequent (P = 0.018). Anti-P was found in 23% of 83 patients with active SLE vs 4% of the 55 patients with inactive SLE (Yates corrected P = 0.00479). An association with anti-dsDNA antibodies by Farr assay was observed. Anti-P positive patients had a median Farr of 65 IU/ml (1.4-1240) and Anti-P negative of 12 IU/ml (1.4-992; P-value = 0.0084). During the study only two patients had lupus psychosis and they were Anti-P positive. No association was found with liver disease (six patients, two with Anti-P antibodies) or active glomerulonephritis (22 patients four with Anti-P). Our data shows that the presence of Anti-P antibodies supports the clinical diagnosis of lupus psychosis.

Diagnostic tests for antiribosomal p protein antibodies: a comparative evaluation of immunoblotting and ELISA assays

We compared the clinical sensitivity and specificity of three different methods for the detection of serum antiribosomal P protein (anti-P) antibodies in systemic lupus erythematosus (SLE). Sera from 60 unselected SLE patients, 100 healthy subjects and 100 patients with other rheumatic inflammatory diseases were screened for anti-P antibodies by immunoblotting (IB) on P proteins from Raji cells and by two ELISA assays, one using the C-terminal 22 aminoacid long synthetic peptide (C-22) of P proteins, the other using a multiple antigen peptide (MAP) carrying four copies of the C-terminal 13 aminoacid long P peptide.Anti-P antibodies were found in 20% lupus sera by IB, 16.7% by MAP ELISA and 11.7% by C-22 ELISA. The specificity for SLE diagnosis of the three tests in healthy subjects and other rheumatic diseases was: 100% by IB, 100% (vs healthy subjects) and 97% (vs rheumatic diseases) by C-22 ELISA, 100% by MAP ELISA. The agreement between methods was good; differences in concordance rates were restricted to weak positivities. We observed a high concordance in the results of IB and ELISA methods for anti-P antibody detection. IB on P proteins extracted from human lymphoid cells is more sensitive than both ELISAs; IB and MAP ELISA perform better than the C-22 ELISA in determining weakly positive sera.

The acidic ribosomal P proteins

The acidic ribosomal P proteins (pI 3-4) are unique among ribosomal constituents: the only molecules on the ribosomes existing in multiple copies, they form a hetero-oligomeric complex (P1/P2)(2) recognizable as a lateral protuberance on the 60S ribosomal subunit, which is thought to be directly involved in interactions with elongation factors during the course of protein synthesis. The role of P proteins in translation is still vague; however, they might possess two functional roles-the proteins may increase performance of ribosomes and/or change ribosomal specificity toward different subset of mRNAs. Furthermore, there are also indications that P proteins might be involved in transcription and DNA repair. Also, P proteins are important antigens in autoimmune diseases, infections caused by protozoan parasites, and in molds.

Autoantibodies to ribosomal P proteins in systemic lupus erythematosus

Autoantibodies to ribosomal P proteins (anti-P) are directed against three ribosomal phosphoproteins (P0, P1, and P2) and are believed to be specific markers for systemic lupus erythematosus (SLE), particularly with neuropsychiatric manifestations. The objective of this study was to determine the rate of occurrence and clinical significance of anti-P in Tunisian patients.

METHODS

We included 100 Tunisian patients with SLE whose sera were received between January 1998 and December 2000 by the immunology laboratory of the Charles Nicolle Teaching Hospital in Tunis, Tunisia, and were tested for anti-P. An immunodot technique based on a synthetic protein shared by all ribosomal phosphoproteins was used.

RESULTS

Sera from 22 (22%) patients were positive for anti-P. This rate is consistent with the literature. We found no statistically significant associations between anti-P and specific manifestations of SLE. CONCLUSION. We found that anti-P were significantly associated with anti-Sm and anti-RNP, as reported previously. The significance of these associations remains debatable.