A CSF disease-associated macrophage signature defines progressive multiple sclerosis

Progression in multiple sclerosis (MS) often corresponds to irreversible disability in MS patients. Cellular changes in the cerebrospinal fluid (CSF) have provided biomarkers and mechanisms in relapsing-remitting MS (RRMS) but remain understudied in primary and secondary progressive MS (summarized herein as PMS).

We combined retrospective flow cytometry of CSF cells from RRMS (n = 169), PMS (n = 56), and non-inflammatory controls (n = 74) with prospective CSF single-cell transcriptomics of 35 individuals (11 controls, 12 RRMS, and 12 PMS) and with confirmatory CSF ELISA. Available CSF single-cell data from age-matched and Alzheimer's disease (AD) patients served as additional controls.

Proportions of CD14⁺ monocytes in CSF are increased in PMS and correlated with clinical surrogate markers of progression. Transcriptionally, these monocytes resembled border-associated macrophages (BAM)-like cells with a chronically activated antigen-presenting phenotype. Additionally, these monocytes shared some features with disease-associated microglia/macrophages (DAM), previously identified in neurodegeneration. Induction of DAM-associated molecules, including transcribed and soluble TREM2 (sTREM2), characterized secondary progressive MS (SPMS) and supported its differential diagnosis.

We thus identified MS stage-specific CSF signatures and shared cellular features of degeneration detectable in CSF of PMS patients.