Recommendations for the use of molecular diagnostics in the diagnosis of allergic diseases.

Summary: The Study Group on Allergology of the Italian Society of Clinical Pathology and Laboratory Medicine (SIPMeL) and the Associazione Italiana degli Allergologi e Immunologi Territoriali e Ospedalieri (AAIITO) developed the present recommendations on the diagnosis of allergic diseases based on the use of molecular allergenic components, whose purpose is to provide the pathologists and the clinicians with information and algorithms enabling a proper use of this second-level diagnostics. Molecular diagnostics allows definition of the exact sensitization profile of the allergic patient. The methodology followed to develop these recommendations included an initial phase of discussion between all the components to integrate the knowledge derived from scientific evidence, a revision of the recommendations made by Italian and foreign experts, and the subsequent production of this document to be disseminated to all those who deal with allergy diagnostics.

An effective algorithm for the serological diagnosis of idiopathic inflammatory myopathies: The key role of anti-Ro52 antibodies.

BACKGROUND: Patients with suspected idiopathic inflammatory myopathies (IIM) are commonly tested for the presence of anti-nuclear antibodies (ANA) by indirect immunofluorescence (IIF) on HEp-2 cell substrates. However, ANA-IIF false negative tests may occur in IIM because some antigens, such as Jo1 and Ro52, may be scarcely expressed on HEp-2 cells. In addition, cytoplasmic staining is often not appropriately investigated by a specific antibody assay, leading to decreased clinical sensitivity of the ANA test. We evaluated the diagnostic impact of different strategies using different combination of myositis-related autoantibody tests. METHODS: Sera from 51 patients with an established diagnosis of IIM were tested for ANA by IIF on HEp-2 cells and for myositis-specific antibodies (MSA) and myositis-associated antibodies (MAA) by lineblot methods. RESULTS: Forty-four/51 (86.3%) samples tested positive with at least one of the three methods and seven were negative with all methods. Of the 44 positive samples, 9 (20.5%) tested negative for the ANA-IIF test and positive for MAA/MSA. Anti-Ro52 were the most prevalent autoantibodies in IIM patients (21/51; 41%), frequently associated with anti-Jo1 antibodies (13/21; 62%). 13 (16%) anti-Ro52 and anti-Jo1 negative samples were reactive to MSA. CONCLUSIONS: Our findings suggest that when IIM is clinically suspected, the optimal diagnostic algorithm is to associate the ANA-IIF screening test with a specific test for anti-Ro52 and anti-Jo1 antibodies. Should all these tests be negative, serological tests for MSA are recommended.

Definition of the upper reference limit for thyroglobulin antibodies according to the National Academy of Clinical Biochemistry guidelines: comparison of eleven different automated methods.

PURPOSE: In the last two decades, thyroglobulin autoantibodies (TgAb) measurement has progressively switched from marker of thyroid autoimmunity to test associated with thyroglobulin (Tg) to verify the presence or absence of TgAb interference in the follow-up of patients with differentiated thyroid cancer. Of note, TgAb measurement is cumbersome: despite standardization against the International Reference Preparation MRC 65/93, several studies demonstrated high inter-method variability and wide variation in limits of detection and in reference intervals. Taking into account the above considerations, the main aim of the present study was the determination of TgAb upper reference limit (URL), according to the National Academy of Clinical Biochemistry guidelines, through the comparison of eleven commercial automated immunoassay platforms. METHODS: The sera of 120 healthy males, selected from a population survey in the province of Verona, Italy, were tested for TgAb concentration using eleven IMA applied on as many automated analyzers: AIA-2000 (AIA) and AIA-CL2400 (CL2), Tosoh Bioscience; Architect (ARC), Abbott Diagnostics; Advia Centaur XP (CEN) and Immulite 2000 XPi (IMM), Siemens Healthineers; Cobas 6000 (COB), Roche Diagnostics; Kryptor (KRY), Thermo Fisher Scientific BRAHMS, Liaison XL (LIA), Diasorin; Lumipulse G (LUM), Fujirebio; Maglumi 2000 Plus (MAG), Snibe and Phadia 250 (PHA), Phadia AB, Thermo Fisher Scientific. All assays were performed according to manufacturers' instructions in six different laboratories in Friuli-Venezia Giulia and Veneto regions of Italy [Lab 1 (AIA), Lab 2 (CL2), Lab 3 (ARC, COB and LUM), Lab 4 (CEN, IMM, KRY and MAG), Lab 5 (LIA) and Lab 6 (PHA)]. Since TgAb values were not normally distributed, the experimental URL (e-URL) was established at 97.5 percentile according to the non-parametric method. RESULTS: TgAb e-URLs showed a significant inter-method variability. Considering the same method, e-URL was much lower than that suggested by manufacturers (m-URL), except for ARC and MAG. Correlation and linear regression were unsatisfactory. Consequently, the agreement between methods was poor, with significant bias in Bland-Altman plot. CONCLUSIONS: Despite the efforts for harmonization, TgAb methods cannot be used interchangeably. Therefore, additional effort is required to improve analytical performance taking into consideration approved protocols and guidelines. Moreover, TgAb URL should be used with caution in the management of differentiated thyroid carcinoma patients since the presence and/or the degree of TgAb interference in Tg measurement has not yet been well defined.

Cutting-edge issues in celiac disease and in gluten intolerance.

Celiac disease (CD) is a gluten-dependent immune-mediated disease with a prevalence in the general population estimated between 0.3% and 1.2%. Large-scale epidemiological studies have shown that only 10-20% of cases of CD are identified on the basis of clinical findings and that laboratory tests are crucial to identify subjects with subtle or atypical symptoms. The correct choice and clinical use of these diagnostic tools may enable accurate diagnosis and early recognition of silent CD cases. In this review, we have considered some relevant aspects related to the laboratory diagnosis of CD and, more extensively, of gluten intolerance, such as the best combination of tests for early and accurate diagnosis, the diagnostic role of new tests for detecting antibodies against neoepitopes produced by the transglutaminase-gliadin complex, the forms of non-celiac gluten intolerance (gluten sensitivity), and the use and significance of measuring cytokines in CD.

Detection of a novel 20 kDa shrimp allergen showing cross-reactivity to house dust mites.

BACKGROUND: Allergy to crustacean shellfish is one of the most common IgE-mediated food allergies, and tropomyosin has been identified as the major allergen. However, not all subjects affected by this allergy are IgE-positive to tropomyosin. AIMS: To evaluate whether sera of patients with shrimp allergy but negative for tropomyosin react to other allergen(s); and to evaluate the role such allergen(s) may play in cross-reactivity between crustaceans and house dust mites (HDMs). METHODS: Three different pools of sera-one from subjects with shellfish allergy and HDMs positivity, but negative for recombinant and native tropomyosin (rPen a 1 and nPen m 1) (Pool 2); a second from subjects with tropomyosin and HDMs positivity (Pool 1); and the last from subjects allergic only to HDMs (Pool 3) were submitted to immunoblotting. Subsequently, a 20 kDa protein- enriched fraction of shrimp extract was used at two different concentrations (10 and 100 microg/mL) to pre-absorb the Pool 2 serum and to evaluate, by ELISA assay, the level of inhibition on shrimp and HDMs-coated wells, respectively. RESULTS: The Pool 2 serum showed IgE reactivity against a 20 kDa component. Its pre-absorption with an enriched fraction of 20 kDa protein caused an inhibition of 56% in IgE binding to shrimp extract at a concentration of 100 microg/mL, and of 14% and 35% to HDMs extract at concentrations of 10 and 100 microg/mL, respectively, as measured by ELISA assay. CONCLUSIONS: The 20 kDa component seems to be a new crustacean allergen and it could play a role in cross-reactivity with HDMs.

Study on the possible role of the -174G>C IL-6 promoter polymorphism in predicting response to rituximab in rheumatoid arthritis.

OBJECTIVE: Identification of genetic biomarkers of response to biologics in rheumatoid arthritis (RA) is a relevant issue. The -174G>C interleukin-6 (IL-6) promoter polymorphism was investigated in RA patients treated with rituximab (RTX), being IL-6 a key cytokine for B cell survival and proliferation, thus possibly implicated in rituximab efficacy. METHODS: The study was conducted in a real-life retrospective cohort of 142 unselected RA patients (120F/22M) treated with RTX and referred to 7 rheumatologic centres in the north of Italy. One hundred and thirteen (79.6%) patients were rheumatoid factor (RF)-positive and 112 (78.9%) were anti-CCP antibodies positive. The response to therapy was evaluated at the end of the sixth month after the first RTX infusion, by using both the EULAR criteria (DAS28) and the ACR criteria. The IL-6 -174G>C promoter polymorphism was analyzed by RFLP following previously reported methods. RESULTS: Lack of response to RTX at month +6 by EULAR criteria was more prevalent in RA patients with the IL-6 -174 CC genotypes (9/21, 42.8%), than in the GC/GG patients (23/121, 19.0%) (OR 3.196, 95% CI=1.204-8.485; p=0.0234). Similar results were found when evaluating the response by ACR criteria. No differences were found in RA duration, baseline DAS28, baseline HAQ, RF status, anti-CCP status according to the different IL-6 -174 genotypes. CONCLUSION: IL-6 promoter genotyping may be useful to better plan treatment with RTX in RA. Larger replication studies are in course to confirm these preliminary results.

BLyS and April serum levels in patients with autoimmune thyroid diseases.

Elevated B-Lymphocyte Stimulator (BLyS) and April (a proliferation-inducing ligand) expressions characterize several autoimmune diseases. We here analysed the possible role of BLyS and April in autoimmune thyroid diseases (AITD), comprising Hashimoto's thyroiditis (HT) and Graves' disease (GD). Seventy-seven patients with AITD and 77 blood donors (HBD) were enrolled in the study. Serum BLyS and April levels were assessed by ELISA. Results indicated a significant upregulation of BLyS in AITD patients (1.12+/-0.39 ng/ml versus 0.666+/-0.240 ng/ml in HBD; p<0.0001), with GD patients presenting higher BLyS levels than HT patients (1.22+/-0.42 ng/ml versus 1.07+/-0.38 ng/ml; p=0.0393). In contrast, April levels were downregulated, but only in HT patients [9.9+/-36.6 (median 0) ng/ml versus 7.4+/-22.1 (median 1.16) ng/ml in HBD; p=0.003; and versus 4.2+/-5.9 ng/ml (median 0.9) ng/ml in GD; p=0.0353]. In HT patients, Levo-thyroxine supplementation further increased BLyS and tended to normalize April levels. Neither BLyS nor April did correlate with the levels of the pathognomonic autoantibodies (TPOAb, TgAb, TRAb). Data are preliminary, but, for the first time, we provide the analyses of BLyS and April levels in AITD patients, suggesting new tools for the diagnosis, prognosis and possible therapeutic management of AITD.

Diagnostic accuracy of IgA anti-tissue transglutaminase antibody assays in celiac disease patients with selective IgA deficiency.

Clinical studies have estimated a 10- to 20-fold increased risk for celiac disease (CD) in patients with selective IgA deficiency (SIgAD). For this reason, screening for CD is mandatory in SIgAD patients, but it represents a special challenge since the specific IgA class antibodies against gliadin (AGA), endomysium (EMA), and tissue-transglutaminase (tTG) are not produced in patients with CD. IgG class counterparts of these antibodies may be informative; in particular IgG EMA has been demonstrated to be a valid marker for diagnosing CD in SIgAD cases, but it is not used much in clinical laboratories, because it is cumbersome and involves some technical difficulties. Even if it was widely used in clinical laboratories, the measuring of IgG AGA has shown a less-than-optimum diagnostic accuracy, so that now it tends to be substituted by tests for anti-tTG IgG, for which the few available studies have shown diagnostic performances superior to AGA. Since it is not known whether various available methods for measuring IgG anti-tTG antibodies offer similar diagnostic performances, we have compared the results obtained from nine second-generation commercial methods (D-tek, Phadia, Immco, Orgentec, Radim, Euroimmun, Inova, Aesku, Generic Assays), measuring IgG anti-tTG antibodies in 20 patients with CD and SIgAD and in 113 controls (9 patients with SIgAD without CD, 54 patients with chronic liver disease, and 50 healthy individuals). Diagnostic sensitivity, calculated by means of ROC plot analysis, ranged between 75% and 95%, and specificity ranged from 94% to 100%. In the same population, the diagnostic sensitivity and specificity of AGA IgG were 40% and 87%, respectively. Even though they perform differently, all IgG anti-tTG methods evaluated are reliable serological assays for the diagnosis of CD in SIgAD patients, with diagnostic accuracy superior to the AGA IgG method. The methods that use a mix of tTG and gliadin peptides as the antigenic preparation have a specificity slightly lower than that of the methods that use only tTG.

Anti-prothrombin antibodies predict thrombosis in patients with systemic lupus erythematosus: a 15-year longitudinal study.

OBJECTIVE: To evaluate the role of anti-prothrombin (anti-PT) antibodies in predicting thrombosis in patients with systemic lupus erythematosus (SLE). METHODS: An inception cohort of 101 SLE patients (12 males, 89 females; mean age 30 +/- 8 years), was considered. Clinical and laboratory evaluations were regularly performed during a 15-year follow-up (median 108 months) with a special focus on thromboembolic events. Serum samples were collected at time of diagnosis and at least once a year thereafter. IgG and IgM anti-PT, anti-cardiolipin (aCL) and anti-beta(2)glycoprotein I (beta(2)GPI) antibodies were measured by enzyme-linked immunosorbent assay (ELISA); lupus anticoagulant (LAC) was assayed by the dilute Russell's viper venom time and activated partial thromboplastin time tests. The analytical specificity of anti-PT ELISA was investigated. The timing of thrombosis occurrence was calculated using the Kaplan-Meier method. RESULTS: In the 15-year follow-up, thrombosis occurred in 14 out of the 101 patients: venous thrombosis in nine cases and arterial thrombosis in five. IgG and/or IgM anti-PT, anti-beta(2)GPI and aCL antibodies, and LAC activity were detected in ten, nine, seven, and nine cases, with sensitivity for thrombosis of 71.4%, 64.3%, 50% and 64.3%, respectively. Thrombosis-free survival was 90% at 5 years and 85.8% at 10 and 15 years, respectively. Thrombosis was predicted by anti-PT (P = 0.001), anti-beta(2)GPI antibodies (P = 0.002) and LAC activity (P = 0.001). Moreover, the risk of thrombosis progressively increased with the number of positive antiphospholipid antibody tests. The presence of four positive antibody tests was associated with a risk of thrombosis thirtyfold higher than in their absence. CONCLUSIONS: This longitudinal study shows that IgG anti-PT antibodies are predictors of thrombosis in SLE patients.

Low specificity of anti-tissue transglutaminase antibodies in patients with primary biliary cirrhosis.

The association between celiac disease (CD) and primary biliary cirrhosis (PBC) is well documented in medical literature; however, a high frequency of false positive results of the anti-transglutaminase (anti-tTG) test has been reported in patients with PBC. To verify if the positive results for anti-tTG autoantibody are false positives due to cross reactivity with mitochondrial antigens, we studied 105 adult patients affected with PBC, positive for anti-mitochondrial M2 antibodies. Anti-tTG IgA antibodies were studied by using six different immunoenzymatic assays that employ the tTG antigen obtained from different sources (human recombinant, placenta, red blood cells, and guinea pig liver). On the whole, 28 out of 105 PBC subjects tested positive for anti-tTG IgA antibodies, but only two were eventually found to be affected by CD; the other 26 were shown to be false positive. The specificity of the various antigenic substrates ranged from 88.5% of the human erythrocytes tTG to 97.1% of the human recombinant tTG. The results of this study showed that a true association between PBC and CD was present in only 2% of the patients and that, in most cases, the false positive results were attributable to the type of substrate utilized in the assay.

Accuracy of semiquantitative immunoenzymatic methods in quantitation of anti-topoisomerase I (Scl-70) antibodies.

Reports of a possible correlation between anti-Scl-70 antibody concentration and clinical manifestations in systemic sclerosis patients have recently appeared in the scientific literature. The goal of our study was to evaluate, by means of a multicenter study, the analytical reliability of immunoassay systems in the quantitative measurement of Scl-70 antibodies. Three blind samples (H, M, L) at different anti-Scl-70 antibody concentrations, and a low concentration antibody serum (LPC) used as a common calibrator, were sent three times in a 6-month time span to 39 Italian clinical laboratories. Each laboratory was asked to calculate dosages following the enzyme-linked immunosorbent assay (ELISA) method they used and report the optical density values of each sample (ODs), of the cutoff serum provided by the manufacturer of the kit used (ODco) and of LPC (ODLPC). The overall analytical imprecision (between methods and between laboratories) of the three different determinations of the values respectively expressed in ODs, ODs/ODco and ODs/ODLPCratio was 47.1, 52.8 and 34.0% for sample H, 56.2, 47.4% and 34% for sample M and 84.6, 86.0 and 86.6% for sample L. The average intra-method analytical imprecision was, respectively, 20.7, 29.8 and 18.6% for sample H, 24.6, 26.5 and 19.3% for sample M, and 30.6, 28.1 and 20.2% for sample L. The commercial ELISA methods currently used to determine the presence of anti-Scl-70 autoantibodies show considerable differences in the quantitative determination. The best results for reproducibility analyses have been obtained when the values were expressed as a ratio between the ODs of the sample and of the common calibrator (ODs/ODLPC). Forward-looking clinical studies that can clarify the usefulness of quantitative determination of anti-Scl-70 antibodies in the monitoring of diffuse scleroderma patients can be performed only when standard serum with a known antibody concentration and calibration curves for quantitative ELISA measurements are made available.

Remission of nephrotic syndrome after thalidomide therapy in a patient with Castleman's disease.

Castleman's is an uncommon lymphoproliferative disorder secondary to lymphoid follicle hyperplasia and marked capillary proliferation with endothelial hyperplasia. This illness can be associated with glomerulonephritis (GN). Here, we report a case with steroid-dependent nephrotic syndrome secondary to proliferative mesangial glomerulonephritis in a patient with Castleman's disease, that was diagnosed several years before. Considering the involvement of IL-6 in Castleman's disease we treated the patient with thalidomide obtaining the remission of the nephrotic syndrome. Our experience suggests a possible role of thalidomide in the treatment of glomerular pathology when a role of IL-6 is hypothesized.

IgA and IgG tissue transglutaminase antibodies in systemic lupus erythematosus.

Systemic lupus erythematosus (SLE) and coeliac disease (CD) are diseases of an autoimmune origin that share the human leukocyte HLA-B8 and HLA-DR3 histocompatibility antigens, yet the co-association of CD with SLE is mainly based on case reports. Thus, the real prevalence of CD in SLE is unclear. The aim of this study was to determine the prevalence of antitissue transglutaminase (anti-tTG) in SLE and the relation between SLE and CD. In this case-control study, 100 patients with SLE, and 120 healthy subjects were studied. Sera from all participants were analysed for the presence of IgA and IgG anti-tTG antibodies using a human recombinant tissue transglutaminase (tTG) immuno-enzymatic assay. Anti-tTG positive patients and controls were further tested for antiendomysial (EMA) antibodies by an indirect immunofluorescence and HLA typing (DQalpha1*0501-DQbeta1*0201 allele determination). Subjects who had EMA or the mentioned allele, underwent duodenal biopsy to confirm a possible diagnosis of CD. Anti-tTG antibodies (IgA or IgG isotypes) were found in three of the 100 SLE patients (overall prevalence of 3%): one had the IgA and two the IgG isotypes. Only 1 of 120 healthy subjects (0.8%) had a low positive reaction for IgA anti-tTG. Only the IgA anti-tTG positive SLE patient was diagnosed as having CD based on a positive IgA-EMA and small bowel biopsy findings. The two IgG anti-tTG positive SLE patients and the IgA anti-tTG positive healthy subject were classified as false positives (EMA negative and HLA DQalpha1*0501-DQbeta1*0201 allele negative). In conclusion, anti-tTG antibodies were found at a low rate in SLE patients and mostly did not indicate the presence of CD. Thus, serological screening for CD is not recommended in SLE, unless a clinical suspicion of CD is present.

The role of antitissue transglutaminase assay for the diagnosis and monitoring of coeliac disease: a French-Italian multicentre study.

AIMS: Tissue transglutaminase (tTG) was recently identified as the major autoantigen in coeliac disease. The aim of this multicentre study was to evaluate the impact of a new immunoenzymatic assay for the detection of IgA anti-tGT antibodies. METHODS: Seventy four Italian and French clinical laboratories participated in this study; anti-tTG IgA with an enzyme linked immunosorbent assay (ELISA) method using guinea pig liver extract as the coating antigen, anti-endomysium IgA autoantibodies (EMA), and total serum IgA were determined in 7948 patients, 1162 of whom had coeliac disease (737 untreated cases and 425 on a gluten free diet). A proportion of the sera were then sent to a reference laboratory for anti-tTG retesting with an ELISA method using recombinant human tTG antigen. RESULTS: Seven thousand four hundred and fifty eight (93.8%) sera were EMA/antiguinea pig tTG concordant (positive or negative); 490 (6.2%) were non-concordant. The sensitivity of EMA and antiguinea pig tTG in the 737 untreated patients with coeliac disease was 92.1% and 94.8%, respectively, and the specificity was 99.8% and 99.2%, respectively. Retesting of the discordant sera showed that of the 162 sera classified as EMA negative/antiguinea pig tTG positive, only 49 were positive for human recombinant anti-tTG, and that 39 of these were also EMA positive. Furthermore, of the 36 sera classified as EMA positive/antiguinea pig tTG negative, only two were confirmed as EMA positive. CONCLUSIONS: The antiguinea pig tTG assay is more sensitive but less specific than EMA, whereas the antihuman recombinant tTG assay is far more specific and just as sensitive as antiguinea pig tTG. Testing for EMA presents considerable interpretative problems and is difficult to standardise.

Anti-dsDNA antibody avidity determination by a simple reliable ELISA method for SLE diagnosis and monitoring.

High avidity anti-dsDNA antibodies are more specific for SLE diagnosis, and more closely associated with renal involvement than intermediate or low-affinity anti-dsDNA antibodies. ELISA methods are largely used to detect anti-dsDNA, but their high sensitivity is inversely related to specificity because they also detect low avidity antibodies. We developed an ELISA assay based on the law of mass action and the competitive binding of dsDNA in solution and coated to microwells with anti-dsDNA antibodies. A simplified Scatchard plot analysis system was used to measure anti-dsDNA antibody avidity which was expressed as apparent affinity constant (Kaa), and quantified in liters per unit (I/U). We prospectively studied 101 consecutive SLE patients, who were followed for 3 years; three serum samples were sequentially collected from each patient during follow-up for determination of IgG anti-dsDNA antibody concentration, and anti-dsDNA avidity. SLE disease activity was estimated using the European Consensus Lupus Activity Measure (ECLAM) index. Sera from 100 healthy subjects and 133 patients with other connective tissue diseases or infectious diseases were also assayed as controls. The mean Kaa in SLE patients was 65.2 +/- 47.3 l/U, with no variations over time. Anti-dsDNA-positive SLE patients had higher Kaa values (79.1 +/- 46.8) than anti-dsDNA negative patients (27.2 +/- 20.1; P < 0.001). No correlation emerged between anti-dsDNA avidity and the ECLAM activity index score. Avidity was significantly higher in patients with renal involvement vs patients without this complication (78.2 +/- 50 vs 59.9 +/- 45.6 l/U; P = 0.0013). This simple ELISA method could be very useful in the diagnostic phase to differentiate high avidity anti-dsDNA autoantibodies that are characteristically found in SLE patients from low avidity antibodies that can also be found in other inflammatory diseases. Moreover, our data confirm the predictive value of high avidity anti-dsDNA antibodies for the development of lupus nephritis.

IgA and IgG tissue transglutaminase antibody prevalence and clinical significance in connective tissue diseases, inflammatory bowel disease, and primary biliary cirrhosis.

An association between celiac disease (CD) and other autoimmune diseases such as connective tissue diseases (CTD), inflammatory bowel diseases (IBD), and primary biliary cirrhosis (PBC) has been reported in several studies. However, a high rate of false positives in autoantibody testing was noted, especially when tissue transglutaminase (tTG) from guinea pig liver was used. Thus, the real prevalence of CD in CTD, IBD, and PBC is unclear. In a case-control study, 400 patients with CTD, 170 with IBD, 48 with PBC, and 120 healthy subjects were investigated for CD by the analysis of IgA and IgG tTG antibodies using the more specific human recombinant tTG immunoenzymatic assay. Patients and controls with positive findings were further tested for antiendomysial antibodies by indirect immunofluorescence and HLA typing, and those found positive by either of these tests underwent duodenal biopsy to confirm a possible diagnosis of CD. Twelve patients were positive for IgA or IgG tTG antibodies, showing an overall prevalence of 1.9%. Only 1 healthy subject (0.8%) had a low level positive reaction for IgA anti-tTG. Among the 12 patients and the healthy subject, only 2 (1 SLE and 1 ulcerative colitis patient) were subsequently confirmed to be affected with CD by positive EMA, HLA, and small bowel biopsy findings. The highest rate of false positives was found in PBC patients (10.4%). For these reasons, serological screening testing for CD is not recommended in CTD patients or in subjects affected with IBD or PBC, unless there is a relevant clinical suspicion of CD.

Evaluation of a new automated enzyme fluoroimmunoassay using recombinant plasmid dsDNA for the detection of anti-dsDNA antibodies in SLE.

ELISA methods to detect anti-double-stranded DNA (anti-dsDNA) antibodies are highly sensitive, but are less specific for the diagnosis of SLE than the immunofluorescence test on Crithidia luciliae (CLIFT) and the Farr assay because they also detect low-avidity antibodies. This study evaluated the specificity, sensitivity, positive predictive value (PPV), and negative predictive value (NPV) of a new automated fluoroimmunoassay (EliA dsDNA; Pharmacia, Freiburg, Germany). We compared the results with those obtained using a commercial CLIFT and an in-house anti-dsDNA IgG ELISA method, and verified its putative ability to detect only high-avidity anti-dsDNA antibodies. Sera from 100 SLE patients and 120 controls were studied. The control group included 20 healthy donors, 70 patients with other rheumatic diseases (32 systemic sclerosis (SSc); 18 primary Sjögren syndrome (pSS), 20 rheumatoid arthritis (RA)), and 30 patients with various infectious diseases (ID). Anti-dsDNA avidity was estimated using an ELISA method based upon the law of mass action, and a simplified Scatchard plot analysis for data elaboration; the apparent affinity constant (Kaa) was calculated and expressed as arbitrary units (L/U). Sensitivity, specificity, PPV, and NPV for SLE were 64%, 95.8%, 93.8% and 72.7%, respectively, for the EliA anti-dsDNA assay; 55%, 99.2%, 98.5%, and 68.8%, respectively, for the CLIFT; and 64%, 93.3%, 90.6%, and 72.3%, respectively, for the in-house ELISA. Although EliA anti-dsDNA was positive mainly in SLE patients with high- (Kaa>80 L/U) and intermediate- (Kaa 30-80 L/U) avidity antibodies (45.3% and 49.9%, respectively), it was also positive in five (7.8%) SLE patients with low-avidity anti-dsDNA antibodies, and five controls (three SSc, one pSS, and one ID) (mean Kaa = 16.4 +/- 9.04 L/U). In conclusion, EliA anti-dsDNA assay showed a higher sensitivity than the CLIFT, and a good specificity and PPV for SLE. Its putative ability to detect only high-avidity anti-dsDNA antibodies remains questionable.

Autoantibody detection in scleroderma patients. Diagnostic and analytical performances of a new coupled particle light scattering immunoassay.

OBJECTIVE: We evaluated the diagnostic and analytical performance of the Coupled Particle Light Scattering technology applied to the detection of anti-topoisomerase I (anti-Scl70) and anti-CENP-B autoantibodies. METHODS: The Scl70 antigen was obtained by recombinant DNA procedures using a prokaryotic expression system; CENP-B was a Baculovirus-expressed recombinant protein. Anti-centromere and anti-Scl70 antibodies were assayed in serum samples from 288 patients, of whom 123 had systemic sclerosis/scleroderma and 165 constituted the control groups (including patients with other connective tissue diseases, viral infections, Lyme disease, and healthy subjects). RESULTS: The sensitivity was 98.8% (confidence interval, 96-101%) for anti-Scl70 and 100% (99.6-100%) for anti-CENP-B; the specificity was 99.0% (98-100%) and 100% (99.9-100%) for anti-Scl70 and anti-CENP-B, respectively. The intra-assay coefficient variations (CV) ranged from 3.8 to 9.2% for anti-Scl70, and from 2.8 to 8.0% for anti-CENP-B. Inter-assay CVs were 8.1 to 12.0% for anti-Scl70, and 4.7 to 10.5% for anti-CENP-B. In 3 patients, coexpression of both antibodies was observed. CONCLUSION: The results of this study demonstrate that the light scattering technology is also applicable to the detection of autoantibodies to intracellular antigens for the diagnosis of autoimmune rheumatic diseases.

[Laboratory diagnosis of autoimmune thyroid disease]. / Diagnostica di laboratorio delle tireopatie autoimmuni.

Assay of the anti-thyroperoxidase (TPO), anti-thyroglobulin (Tg), and anti-TSH receptor antibodies constitutes the basis of the laboratory diagnostic work-up for autoimmune thyroid diseases. However, although these antibodies have been routinely assayed in serum for more than 40 years with increasingly reliable methods, it still exists a wide analytical variability that influences their correct diagnostic use. We analysed the biochemical, physiopathological and clinical aspects of the thyroid antigen-anti body systems, and propose the following guidelines for using autoantibody tests and analytical assay methods: a) assay of anti-TPO with third generation ultrasensitive method should constitute the main test for the diagnosis of autoimmune thyroid diseases. Assay of anti-M antibodies should be considered obsolete because even purified microsome preparations contain traces of contaminants (Tg and other antigens) that make the test aspecific; b) assay of anti-Tg antibodies may be limited to patients with suspect AITD and negative for anti-TPO antibodies, and patients undergoing thyroglobulin assay, because anti-Tg autoantibodies may interfere in the assay of the molecule in the immunometric test; c) assay of the anti-TSH receptor antibodies is used to diagnose Basedow's disease, and atrophic chronic thyroiditis; d) it is appropriate to use normal reference values adjusted for age and gender.

New coupled-particle light-scattering assay for detection of Ro/SSA (52 and 60 kilodaltons) and La/SSB autoantibodies in connective tissue diseases.

The diagnostic and analytical performance of the coupled-particle light-scattering assay in detecting anti-Ro/SSA autoantibodies (the 60-kDa [Ro60] and the 52-kDa [Ro52] antibodies) and anti-La/SSB autoantibodies was evaluated. The antigens were obtained by recombinant DNA procedures to include the most immunogenic epitopes for each protein by using a prokaryotic expression system. Serum samples from 151 patients with connective tissue diseases and 52 control subjects (including patients with viral infections, patients with Lyme disease, and healthy subjects) were studied. Sensitivities for detection of anti-Ro/SSA and anti-La/SSB were 88.2 and 95.2%, respectively; specificities were 97.6 and 98.1%, respectively. The intra-assay coefficient of variation (CV) ranged from 4.3 to 10.9% for anti-Ro/SSA and from 2.8 to 12.5% for anti-La/SSB; interassay CVs ranged from 6.5 to 13.2% and from 8.2 to 14.5%, respectively. Among the anti-Ro/SSA-positive samples, Ro60 was recognized by 66% of the test sera and Ro52 was recognized by 95% of the test sera. Thirty-four percent of the Ro/SSA-positive sera were reactive only with the Ro52 antigen, indicating that anti-Ro52 is the most common antibody specificity recognized by anti-Ro/SSA autoantibodies. No differences were found between the prevalences of anti-Ro60 and anti-Ro52 in relation to systemic lupus erythematosus or Sjögren's syndrome. The results of the present study indicate that this new immunoassay is an efficient diagnostic tool for the detection of anti-Ro/SSA and anti-La/SSB antibodies in patients with autoimmune disorders.