Autoantibody Diagnostics in Neuroimmunology: Experience From the 2018 Italian Neuroimmunology Association External Quality Assessment Program.

Matteo Gastaldi,Fulvio Baggi,Diego Franciotta,Silvia Scaranzin,Antonio Uccelli,Francesca Andreetta,Elisabetta Zardini

doi:10.3389/fneur.2019.01385

Abstract

Background: Neuroimmunology has impressively expanded in the past decade. Novel assays, especially cell-based assays (CBAs) can detect conformational antibodies (Abs) recognizing antigens in their native conformation. Generally, the availability of in-house and of commercial tests has improved the diagnostics, but introduced demanding laboratory tasks. Hence, standardization and quality controls represent a key step to promote accuracy. We report on the results of the 2018 external quality assessment program (EQAP) organized by the Italian Neuroimmunology Association.Methods: EQAP regarded 10 schemes, including oligoclonal bands (OCBs), intracellular-neuronal (ICN)-Abs, neuronal-surface (NS)-Abs, aquaporin-4 (AQP4)-Abs, myelin oligodendrocyte glycoprotein (MOG)-Abs, myelin-associated glycoprotein (MAG)-Abs, ganglioside-Abs, acetylcholine-receptor (AChR)-Abs, and muscle-specific-kinase (MuSK)-Abs, and 34 laboratories. Assays were classified as tissue-based assays (TBAs), solid-phase assays (SPAs), liquid-phase assays (LPAs), and CBAs. Thirty-three samples were provided.Results: Three-quarter of the tests were commercial. Median accuracy for the laboratories was 75% (range 50–100). In 8/10 schemes, at least one sample provided discrepant results. Inter-laboratory “substantial agreement” was found in 6/10 schemes (AChR, MuSK, MAG, AQP4, MOG, and NS-Abs), whereas the worst agreements regarded OCBs and ganglioside-Abs. Both commercial and in-house assays performed better in experienced laboratories.Conclusions: Assays could be divided in (a) robust commercial tests with substantial inter-laboratory agreement (MAG-Abs; AChR- and MuSK-Abs); commercial/“in-house” tests with (b) partial inter-laboratory agreement (AQP4-Abs, MOG-Abs, NS-Abs, ICN-Abs), and (c) with large inter-laboratory disagreement (OCBs, ganglioside-Abs). This real-life snapshot of the neuroimmunology test performances highlights shortcomings attributable to technician-dependent performances, assay structural limitations, and errors in test interpretations.

Highlights

External quality assessment (EQA) testing is part of a wider educational approach aimed to improve and monitor quality in laboratory diagnostics
The first one required to establish presence or absence of oligoclonal IgG bands (OCBs) in each of the four paired serum and CSF controls (8 samples), whilst the Conclusions In line with the other previous programs on OCBs promoted by Association of Neuroimmunology (AINI), this EQA revealed the difficulties in detecting OCBs in critical samples
Results of AINI EQAS As most laboratories used the commercial test that includes only the most frequent neuronal surface antibodies (NS-Abs) (NMDAR-Abs, leucine rich glioma inactivated-1 (LGI1)-Abs, CASPR2Abs, AMPAR-Abs, and GABABR-Abs), the EQA scheme was restricted to these Abs

Summary

Introduction

External quality assessment (EQA) testing is part of a wider educational approach aimed to improve and monitor quality in laboratory diagnostics. Such autoantibodies preferentially bind antigens when their tertiary structure is preserved This has revolutionized the neuroimmunology diagnostics, with the diffusion of “conformational” tests, such as cell-based assays (CBAs) and immunohistochemistry on lightly-fixed brain tissues for the diagnosis of autoimmune encephalitis [4], and for the differential diagnosis of the acquired demyelinating diseases of the CNS, including multiple sclerosis [5]. Novel tests using CBAs have been implemented, showing high sensitivity in detecting AChRand MuSK-Abs in LPA antibody-negative patients [70, 71] This advantage is likely linked to the antigen clustering at the cell surface, improving the binding of divalent low-affinity AChR-Abs. This advantage is likely linked to the antigen clustering at the cell surface, improving the binding of divalent low-affinity AChR-Abs Such tests are performed on live cells, and they are necessarily “in-house” and non-standardized. Commercial ELISAs are available for the detection of both AChR- and MuSK-Abs, but their performances are inferior to those of RIAs [69]

Methods

Results

Conclusion