Detection Methods for Autoantibodies in Suspected Autoimmune Encephalitis

Abstract

This review provides an overview on different antibody test methods that can be applied in cases of suspected paraneoplastic neurological syndromes (PNS) and anti-neuronal autoimmune encephalitis (AIE) in order to explain their diagnostic value, describe potential pitfalls and limitations, and discuss novel approaches aimed at discovering further autoantibodies. Onconeuronal antibodies are well-established biomarkers for PNS and may serve as specific tumor markers. The recommended procedure to detect onconeuronal antibodies is a combination of indirect immunohistochemistry on fixed rodent cerebellum and confirmation of the specificity by line assays. Simplification of this approach by only using line assays with recombinant proteins bears the risk to miss antibody-positive samples. Anti-neuronal surface antibodies are sensitive and specific biomarkers for AIE. Their identification requires the use of test methods that allow the recognition of conformation dependent epitopes. These commonly include cell-based assays and tissue based assays with unfixed rodent brain tissue. Tissue based assays can detect most of the currently known neuronal surface antibodies and thus enable broad screening of biological samples. A complementary testing on live neuronal cell cultures may confirm that the antibody recognizes a surface epitope. In patients with peripheral neuropathy, the screening may be expanded to teased nerve fibers to identify antibodies against the node of Ranvier. This method helps to identify a novel subgroup of peripheral autoimmune neuropathies, resulting in improved immunotherapy of these patients. Tissue based assays are useful to discover additional autoantibody targets that play a role in diverse autoimmune neurological syndromes. Antibody screening assays represent promising avenues of research to improve the diagnostic yield of current assays for antibody-associated autoimmune encephalitis.

Single‐center study of autoimmune encephalitis‐related autoantibody testing in Hungary

“…Anti-NMDAR encephalitis was the most common subtype, followed by anti-LGI1, anti-GABA B R, and anti-Caspr2 encephalitis, which is in agreement with previous reports (Gable, Sheriff, Dalmau, Tilley, & Glaser, 2012;van Sonderen et al, 2017). Our data regarding the age and sex of AIE patients agree with the data published in the literature (Ricken et al, 2018).…”

“…In conclusion, our data are in agreement with previous reports on the frequency and distribution of AIE‐related autoantibodies, and detection of which can significantly aid the diagnosis of AIE and suggests treatment strategies. Early immunotherapy is often effective and can reduce the severity of AIE, promote recovery and decrease the risk of relapse (Crisp, Kullmann, & Vincent, ; Dalmau & Graus, ; Ricken et al, ; Varley, Taylor, & Irani, ). As the number of patients affected by AIE is increasing and the spectrum of the newly identified autoantibodies broadens, it is important to employ reliable laboratory tests that allow accurate diagnosis to be made.…”

“…About 30 µl of the samples (sera diluted 1:10 or CSF undiluted) were incubated on the BIOCHIP containing the six transfected cell lines for 30 min at room temperature, followed by two washing steps with PBS Tween‐20 buffer (included in the kit) for 5 min. For secondary labeling, 25 µl of anti‐Human IgG (Fc‐specific)‐FITC antibody specifically recognizing Fc fragment of all human IgG subclasses (IgG is the most frequently associated immunoglobulin isotype in AIE (Ricken et al, )), included in the kit, was applied for 30 min at room temperature. After two washes for 5 min, glycerol (included in the kit) was used for covering the slides.…”

“…In conclusion, our data are in agreement with previous reports on the frequency and distribution of AIE-related autoantibodies, and detection of which can significantly aid the diagnosis of AIE and suggests treatment strategies. Early immunotherapy is often effective and can reduce the severity of AIE, promote recovery and decrease the risk of relapse (Crisp, Kullmann, & Vincent, 2016;Dalmau & Graus, 2018;Ricken et al, 2018;Varley, Taylor, & Irani, 2018…”

Searching for Serum Antibodies to Neuronal Proteins in Patients With Myalgic Encephalopathy/Chronic Fatigue Syndrome

“…Binding to live cultured neurons was a good test of the potential pathogenicity of the antibodies, because it detected only those antibodies that could bind in vivo, but was only performed on 60 samples, including the 11 positive samples by immunohistochemistry (IHC). Two sera, both positive by IHC, bound clearly in a typical punctuate pattern ( Figure 2), as shown in many previous studies of cell-surface antibodies 9,10 and supporting the specificity of the IHC binding shown above. Two other sera bound less strongly on IHC and to neurons, but 11 bound on IHC or to neurons but not both.…”