Tissue Immunofluorescence Confirmation of CNS Autoantibodies Identified by Immunoblot or Cell-Based Assay

Abstract Background: While many immunologic targets of autoimmune CNS disease have been identified, autoantibodies to each, are detected only rarely. Therefore, serum is often screened by immunofluorescence assay (IFA) with whole brain tissue before reflexing positive samples to more specific assays for confirmation and identification. The purpose of this study was to compare the sensitivity of immunofluorescence positive staining of whole brain tissue to immunoblot assays (IBAs) and cell-based immunofluorescence assays (CBAs) for the initial detection of autoantibodies associated with paraneoplastic syndrome (PNS) and other autoimmune diseases of the CNS. Methods: All comprehensive paraneoplastic neurological syndrome panel results released from our laboratory over a two-year period (2017-2019) were reviewed. This panel was specifically chosen for these retrospective analyses because of the comprehensive PNS panel’s design; a reflex testing algorithm is not used and a tissue IFAs, IBAs, and CBAs, are run in parallel and independently on all serum samples. Results: For autoantibodies to intracellular targets, tissue IFA results were positive for 47 of 56 (84%) samples that were positive by IBA. In contrast, for autoantibodies to membrane-imbedded antigenic targets, tissue IFA results were positive for only 5 of 14 (35.7%) samples that were positive by CBA. Conclusions: These retrospective analyses suggest that tissue IFAs of serum are more than twice as likely to confirm the presence of IBA identified autoantibodies to intracellular proteins than CBA identified autoantibodies to membrane imbedded protein targets. Moreover, these findings have important implications for the use of tissue IFA screening for the initial detection of CNS autoantibodies.