Brenda B. Suh-Lailam

Anti-NMDA-receptor antibody encephalitis: Performance evaluation and laboratory experience with the anti-NMDA-receptor IgG assay

BACKGROUND Antibodies targeting the NR1 subunit of the N-methyl-d-aspartate-receptor (NMDAR) are considered diagnostic for a novel form of autoimmune encephalitis. We report the validation of a qualitative indirect immunofluorescence antibody (IFA) test for the detection of anti-NMDAR IgG and describe the attributes of antibody-positive patients. METHODS The anti-NMDAR IgG assay (Euroimmun Diagnosika, Lübeck, Germany) was validated with serum and cerebrospinal fluid (CSF) specimens from 30 healthy and 50 disease controls as well as 5 anti-NMDAR IgG-positive individuals. Consecutive specimens (n=1671) for anti-NMDAR IgG antibodies were evaluated and positive specimens titrated to end-point [starting dilutions: CSF; 1:1 and serum; 1:10]. In a subset of antibody-positive patients, we sought clinical information for correlation with diagnostic and treatment outcomes. RESULTS The assay demonstrated excellent performance characteristics in all groups evaluated. Of the 1671 specimens tested, 1389 were unique cases with a positivity rate of 9.0% (n=123). For the antibody-positive samples, the female to male ratio was 2:1 with a prevalence of 46% in the pediatric population (≤17 years). Antibody titers were titrated to end-point for 106/123 specimens [45 CSF, 41 sera, and 20 CSF and serum pairs] with more than 75% having titers greater than 1:10 (CSF) and 1:20 (serum). Overall, high levels of these antibodies showed correlation to disease severity with variable response to treatment in the subset of patients evaluated. CONCLUSION Our data suggests a high prevalence for anti-NMDAR antibody encephalitis irrespective of age and gender in our unselected disease cohort with support for measuring antibody titers in the evaluation of these patients.

A fast and efficient method for quantitative measurement of S-adenosyl-L-methionine-dependent methyltransferase activity with protein substrates.

Modification of protein residues by S-adenosyl-L-methionine (AdoMet)-dependent methyltransferases impacts an array of cellular processes. Here we describe a new approach to quantitatively measure the rate of methyl transfer that is compatible with using protein substrates. The method relies on the ability of reverse-phase resin packed at the end of a pipette tip to quickly separate unreacted AdoMet from radiolabeled protein products. Bound radiolabeled protein products are eluted directly into scintillation vials and counted. In addition to decreasing analysis time, the sensitivity of this protocol allows the determination of initial rate data. The utility of this protocol was shown by generating a Michaelis-Menten curve for the methylation of heterogeneous nuclear ribonucleoprotein K (hnRNP K) protein by human protein arginine methyltransferase 1, variant 1 (hPRMT1v1), in just over 1h. An additional advantage of this assay is the more than 3000-fold reduction in radioactive waste over existing protocols.

Significant differences in the analytic concordance between anti-dsDNA IgG antibody assays for the diagnosis of systemic lupus erythematosus--implications for inter-laboratory testing.

BACKGROUND Anti-double stranded DNA (anti-dsDNA) autoantibodies are considered hallmark of systemic lupus erythematosus (SLE). METHODS To determine concordance between assays for the detection of this marker, we analyzed 100 antinuclear antibody (ANA) positive sera with a homogeneous pattern and titers≥1:160 by indirect immunofluorescence assay (IFA) on HEp-2 cells, 100 consecutive anti-dsDNA IgG ELISA-negative as well as 100 healthy control samples using six commercial ELISAs and the Crithidia luciliae immunofluorescence test (CLIFT). RESULTS The positivity rates for the ELISAs in the ANA positive group ranged from 55.0 to 88.0% with specificities from 84.0 to 98.0%. The CLIFT had a positivity rate of 68.0% and specificity of 84%. In the previously screened anti-dsDNA IgG-negative group, the positivity rates ranged from 1 to 19%. The overall correlations between the ELISAs ranged from 73.0 to 89.5% and varied from 70.0 to 80.0% among specific ELISAs and CLIFT. CONCLUSIONS Our data show variable degree of concordance between anti-dsDNA IgG ELISAs which may significantly impact inter-laboratory testing as well as the diagnosis and management of SLE patients. Although some of the ELISAs show comparable performance to the CLIFT, the degree of concordance between these assays at high antibody levels suggests that CLIFT is still a relevant confirmatory tool.

Challenging Identification of a Novel PiISF and the Rare PiMmaltonZ α1-Antitrypsin Deficiency Variants in Two Patients

OBJECTIVES α1-Antitrypsin (AAT) deficiency is associated with an increased risk for lung and liver disease. Identification of AAT deficiency as the underlying cause of these diseases is important in correct patient management. METHODS AAT deficiency is commonly diagnosed by demonstrating low concentrations of AAT followed by genotype and/or phenotype testing. However, this algorithm may miss novel AAT phenotypes. RESULTS We report two cases of AAT deficiency in two patients: a case of the novel phenotype PiISF, misclassified as PiII by phenotyping, and a case of the rare phenotype PiMmaltonZ misclassified as PiM2Z. CONCLUSIONS These cases highlight the importance of understanding the limitations of a commonly used diagnostic algorithm, use of further gene sequencing in applicable cases, and the potential for underdiagnosis of AAT deficiency in patients with chronic obstructive pulmonary disease.

Efficient cleavage of problematic tobacco etch virus (TEV)-protein arginine methyltransferase constructs.

Protein arginine methyltransferases (PRMTs) are enzymes that are involved in many biological processes. Several studies have shown that the identity of the N-terminal fusion tag affects the substrate selectivity of PRMTs. Therefore, to accurately study substrate recognition, it is imperative that a tagless PRMT be used. However, cleavage of tagged PRMTs has been problematic. We have developed a successful method by which untagged PRMTs can be made using a tobacco etch virus (TEV) cleavage site at the N-terminal domain. This method may be useful for cleaving other challenging target proteins that have the TEV protease recognition site.

Immunoassays for the detection of IgA antibodies to tissue transglutaminase: significance of multiples of the upper limit of normal and inter-assay correlations

Abstract Background: The presence of IgA antibodies to tissue transglutaminase (anti-tTg) is associated with variable risk for celiac disease. The use of common multiples of the upper limit of normal (ULN) has been suggested to optimize diagnostic pathways as well as improve harmonization between assays. Methods: The characteristics of four anti-tTG IgA assays relative to endomysial IgA (EMA) by indirect immunofluorescence assay (IFA) as reference test were assessed. Commutability between anti-tTG immunoassays and/or EMA based on manufacturer’s recommended cut-off values and three common multiples of ULN (3×, 5× and 10×) was also investigated. Sera from 200 patients and 100 healthy individuals were analyzed. Results: At manufacturer’s cut-off; the sensitivities for the tTG assays ranged from 72.5% to 98.6% and specificities from 60.3% to 99.2%. The percent positive agreements between any anti-tTG and EMA or any two anti-tTG immunoassays varied from 56.7% to 98.0% and 46.7% to 100.0%, respectively. At 3×, 5× or 10× ULNs, the inter-rater reliability as measured by Cohen κ between any two anti-tTG assays were quite variable and ranged from 0.28 to 0.96, 0.26 to 0.89 or 0.13 to 0.78, respectively. Furthermore, the percent positive agreements between any two anti-tTg IgA immunoassays ranged from 83.1% to 98.2%, 92.0% to 100%, or 100%, at 3×, 5× or 10×, respectively. Conclusions: Commutability between tTG IgA immunoassays or tTG IgA and EMA is kit-dependent and common multiples of the ULN are not sufficient to correct for inter-assay variations. Many factors influence the performance of anti-tTG IgA assays which limit their commutability.

Comparative analysis of neutrophil gelatinase-associated lipocalin and other laboratory markers for lupus nephritis: a cross-sectional investigation

Background Lupus nephritis is one of the most serious complications of systemic lupus erythematosus. This study evaluates the prevalence and correlation between neutrophil gelatinase-associated lipocalin and other biomarkers associated with renal involvement in systemic lupus erythematosus. Methods Paired serum and urine specimens from 50 suspected systemic lupus erythematosus patients, characterized by antinuclear antibodies detected by indirect immunofluorescence assay and varying positive concentrations of anti-double stranded DNA antibodies by Crithidia luciliae immunofluorescence assay, were investigated. Of these 50 patients, 18 were identified with renal involvement based upon laboratory serology. Patients and healthy control serum samples (n = 50) were also evaluated for high avidity double stranded DNA IgG antibodies, anti-C1q IgG antibodies, and serum creatinine. The prevalence and relationship between biomarkers were evaluated using statistical methods. Results Serum and urine neutrophil gelatinase-associated lipocalin concentrations were significantly elevated in patients compared to controls, with a prevalence of 24% and 36%, respectively. These concentrations were also more markedly increased in systemic lupus erythematosus patients with renal involvement than those without. Spearman’s correlations between neutrophil gelatinase-associated lipocalin and other biomarkers tested ranged from 0.06 to 0.66 in all patients. Combined concordance as determined by Cronbach alpha coefficient between biomarkers was reduced from 0.71 to 0.58 (serum) and 0.62 (urine) when neutrophil gelatinase-associated lipocalin was removed. Conclusions Neutrophil gelatinase-associated lipocalin concentrations are elevated and demonstrate variable associated with other laboratory markers for renal involvement in systemic lupus erythematosus. Prospective longitudinal studies are needed to determine the optimal biomarker combinations for use in routine management of systemic lupus erythematosus patients at-risk for lupus nephritis.