Characterization of neurofibrillary tangle immunophenotype signatures to classify tangle maturity in Alzheimer's disease

INTRODUCTION Tau aggregation into neurofibrillary tangles in Alzheimer's disease (AD) is a dynamic process involving changes in tau phosphorylation, isoform composition, and morphology. To facilitate studies of tangle maturity, we developed an image analysis pipeline to study antibody labeling signatures that can distinguish tangle maturity levels in AD brain tissue. METHODS Using fluorescent immunohistochemistry, we co‐labeled AD brain tissue with four antibodies that bind different tau epitopes. Mean fluorescence intensity of each antibody was measured, and spectral clustering was used to identify tangle immunophenotypes. RESULTS Five distinct tangle populations were identified, and different tangle maturity immunophenotypes were identified with increasing Braak stage. Early tangle immunophenotypes were more prevalent in later affected regions and advanced immunophenotypes were associated with ghost morphology. DISCUSSION Our findings indicate that tangle populations characterized by advanced tau immunophenotypes are associated with higher Braak stage and more mature morphology, providing a new framework for defining tangle maturity levels using tau antibody signatures. Highlights Populations of neurofibrillary tangles exist in Alzheimer's disease. The immunophenotype of neurofibrillary tangle populations relates to their maturity. The most advanced immunophenotypes are associated with higher Braak stage. The most advanced immunophenotypes are associated with ghost morphology. The most immature immunophenotypes are associated with later affected regions.