No replicating evidence for anti‐amyloid‐β autoantibodies in cerebral amyloid angiopathy‐related inflammation

Abstract

Abstract Objective Elevated levels of anti‐amyloid‐β (anti‐Aβ) autoantibodies in cerebrospinal fluid (CSF) have been proposed as a diagnostic biomarker for cerebral amyloid angiopathy‐related inflammation (CAA‐RI). We aimed to independently validate the immunoassay for quantifying these antibodies and evaluate its diagnostic value for CAA‐RI. Methods We replicated the immunoassay to detect CSF anti‐Aβ autoantibodies using CSF from CAA‐RI patients and non‐CAA controls with unrelated disorders and further characterized its performance. Moreover, we conducted a literature review of CAA‐RI case reports to investigate neuropathological and CSF evidence of the nature of the inflammatory reaction in CAA‐RI. Results The assay demonstrated a high background signal in CSF, which increased and corresponded with higher total immunoglobulin G (IgG) concentration in CSF (rsp = 0.51, p = 0.02). Assay levels were not elevated in CAA‐RI patients (n = 6) compared to non‐CAA controls (n = 20; p = 0.64). Literature review indicated only occasional presence of B‐lymphocytes and plasma cells (i.e., antibody‐producing cells), alongside the abundant presence of activated microglial cells, T‐cells, and other monocyte lineage cells. CSF analysis did not convincingly indicate intrathecal IgG production. Interpretation We were unable to reproduce the reported elevation of anti‐Aβ autoantibody concentration in CSF of CAA‐RI patients. Our findings instead support nonspecific detection of IgG levels in CSF by the assay. Reviewed CAA‐RI case reports suggested a widespread cerebral inflammatory reaction. In conclusion, our findings do not support anti‐Aβ autoantibodies as a diagnostic biomarker for CAA‐RI.