Lineage-calibrated peripheral monocyte-derived myeloid states in neurodegenerative disease: Recruitment, lesion decoding, and state persistence

Peripheral monocytes and monocyte-derived macrophages are increasingly implicated in neurodegenerative disease, yet interpretation remains limited by phenotypic convergence with resident microglia, inconsistent lineage attribution, and strong dependence on experimental model and disease stage. We present a structured, lineage-calibrated framework that separates three linked processes: a recruitment gate controlling access to CNS borders and lesions; a lesion-decoding hub through which aggregate, lipid, cytokine, complement, antigenic, hypoxic, and danger-associated inputs are interpreted; and a state-persistence layer in which metabolic and epigenetic reinforcement stabilizes inflammatory, repair-supportive, or hybrid repair-restrictive programs. To make the framework operational, we first provide a cross-disease synthesis and then map representative models of Alzheimer's disease, Parkinson's disease, amyotrophic lateral sclerosis, and multiple sclerosis to their specific recruitment routes, lesion cues, lineage confidence, and functional outcomes. We also distinguish what single-cell or spatial data can infer from what only origin-resolving approaches can establish, and propose practical terminology for studies that cannot perform fate mapping or parabiosis. A worked therapeutic example illustrates why the same recruitment pathway may be harmful during lesion expansion but useful during debris clearance and recovery. The central question is therefore not whether monocytes are present, but which model, compartment, time point, evidentiary tier, and stabilized state justify a disease-modifying claim. This framework links mechanistic evidence to biomarkers, patient stratification, and stage-aware intervention while reducing over-attribution of peripheral origin.