Detection of Autoantibodies Against the Acetylcholine Receptor, Evaluation of Commercially Available Methodologies: Fixed Cell-Based Assay, Radioimmunoprecipitation Assay and Enzyme-Linked Immunosorbent Assay1.

Background/Objective: Myasthenia Gravis (MG) is an autoimmune disorder characterized by pathogenic autoantibodies (AAbs) targeting nicotinic acetylcholine receptors (AChR), disrupting neuromuscular communication. RadioImmunoPrecipitation Assay (RIPA) is recommended to detect AChR AAbs, but its complexity and radioactive requirements limit widespread use. We compare non-RIPA anti-AChR immunoassays, including Cell-Based Assay (CBA) and two ELISA kits, against the gold standard RIPA. Methods/Results: 145 samples were included with medical indication for anti-AChR testing. By the RIPA method, 63 were negative (RIPA-Neg < 0.02 nmol/L), 18 were classified as Borderline (≥0.02 -1 nmol/L), and 64 were positive (RIPA-Pos > 1 nmol/L). The competitive ELISA showed poor agreement with RIPA (Kappa = 0.216). The indirect ELISA demonstrated substantial agreement with RIPA (Kappa = 0.652), with ∼76% sensitivity and ∼94% specificity for MG diagnostic. The CBA, where fixed cells expressing clustered AChR were used as substrate, exhibited almost perfect agreement with RIPA (Kappa = 0.984), yielding ∼98% sensitivity and 96% specificity for MG. In addition, a semiquantitative analysis showed a strong correlation between CBA titration, indirect ELISA, and RIPA levels (r = 0.793 and r = 0.789, respectively). Conclusions: The CBA displayed excellent analytical performance for MG diagnostic when compared to RIPA, making it a potential replacement for RIPA in clinical laboratories. Some solid-phase assays (such as the indirect ELISA applied here), as well as CBA titration, offer reliable options to estimate anti-AChR AAb levels after confirming positivity by the CBA.∥.

"Untargeting" autoantibodies using genome editing, a proof-of-concept study.

Autoantibodies (AAbs) are useful biomarkers and many have direct pathogenic role. Current standard therapies for elimination of specific B/plasma-cell clones are not fully efficient. We apply CRISPR/Cas9 genome-editing to knockout V(D)J rearrangements that produce pathogenic AAbs in vitro. HEK293T cell-lines were established stably expressing a humanized anti-dsDNA Ab (clone 3H9) and a human-derived anti-nAChR-α1 Ab (clone B12L). For each clone, five CRISPR/Cas9 heavy-chain's CDR2/3-targeting guided-RNAs (T-gRNAs) were designed. Non-Target-gRNA (NT-gRNA) was control. After editing, levels of secreted Abs were evaluated, as well as 3H9 anti-dsDNA and B12L anti-AChR reactivities. T-gRNAs editing decreased expression of heavy-chain genes to ∼50-60%, compared to >90% in NT-gRNA, although secreted Abs levels and reactivity to their respective antigens in T-gRNAs decreased ∼90% and âˆ¼ 95% compared with NT-gRNA for 3H9 and B12L, respectively. Sequencing indicated indels at Cas9 cut-site, which could lead to codon jam, and consequently, knockout. Additionally, remaining secreted 3H9-Abs presented variable dsDNA reactivity among the five T-gRNA, suggesting the exact Cas9 cut-site and indels further interfere with antibody-antigen interaction. CRISPR/Cas9 genome-editing was very effective to knockout the Heavy-Chain-IgG genes, considerably affecting AAbs secretion and binding capacity, fostering application of this concept to in vivo models as a potential novel therapeutic approach for AAb-mediated diseases.

A cell-based assay for detection of anti-fibrillarin autoantibodies with performance equivalent to immunoprecipitation.

Anti-fibrillarin autoantibodies are useful for the diagnosis and prognosis of systemic sclerosis (SSc). Anti-fibrillarin produces a clumpy nucleolar pattern in indirect immunofluorescence assay on HEp-2 cells (HEp-2 IFA). Here we develop and validate a reliable cell-based anti-fibrillarin assay (Fibrillarin/CBA) for use in clinical diagnostic laboratories. A TransMembrane Signal was fused to the human fibrillarin gene (TMS-fibrillarin). HEp-2 cells overexpressing transgenic TMS-fibrillarin at the cytoplasmic membrane were used as IFA substrate in the Fibrillarin/CBA. Sixty-two serum samples with nucleolar pattern in the HEp-2 IFA (41 clumpy; 21 homogeneous/punctate) were tested for anti-fibrillarin using Fibrillarin/CBA, immunoprecipitation (IP), line-blot and ELISA. In addition, samples from 106 SSc-patients were evaluated with Fibrillarin/CBA and the results were correlated with disease phenotypes. Thirty-eight of 41 samples with the clumpy nucleolar pattern (92.7%) were positive in the Fibrillarin/CBA, while all 21 samples with other nucleolar patterns were negative. Fibrillarin/CBA results agreed 100% with IP results. Among the 38 Fibrillarin/CBA-positive samples, only 15 (39.5%) and 11 (29%) were positive for anti-fibrillarin in line-blot and ELISA, respectively. Higher frequency of diffuse cutaneous SSc (dcSSc) phenotype (72.7% vs 36.8%; p=0.022), cardiac involvement (36.4% vs 6.5%; p=0.001) and scleroderma renal crisis (18.2% vs 3.3% p = 0.028) was observed in SSc patients with positive compared to negative Fibrillarin/CBA result. Performance of Fibrillarin/CBA in the detection of anti-fibrillarin autoantibodies was comparable to the gold standard IP. Positive Fibrillarin/CBA results correlated with disease phenotypes known to be associated with anti-fibrillarin autoantibodies, underscoring the clinical validation of this novel assay.