Circulating monocytes are directly involved in neuroinflammation of neurodegenerative diseases, but their role remains unclear in the pathophysiology of frontotemporal degeneration (FTLD). Single-cell IsoCode chip proteomic technology has delineated the functional heterogeneity of blood monocytes that may provide the potential to serve as biomarkers in patients with FTLD, with further study and larger patient numbers in the future.
Blood monocytes from age-matched healthy subjects (n = 2) or patients with FTLD (n = 8) were enriched with Pan Monocyte Isolation Kit. Cells were stimulated with LPS at 37°C, 5% CO2 for 24 hours, stained with Alex Fluor 647 or PE-conjugated anti-CD14 or CD16 and loaded into an IsoCode chip pre-patterned with a 32-plex antibody array per cellular microchamber. After 16-hour-on-chip incubation, secreted proteins from ~ 1000 single cells were analyzed by fluorescence ELISA-based assay; polyfunctional cells (co-secretion of 2+ proteins per cell) were analyzed by IsoSpeak software.
CD14+CD16- monocytes exhibited a greater polyfunctionality than CD14+CD16+ subsets, which was observed in both health and disease. The increased polyfunctional CD14+CD16- monocytes had elevated secretions in IL-6, IL-8, MIP-1α, MIP-1β and TNF-α compared to CD14+CD16+ cells. Interestingly, patients with FTLD showed higher polyfunctional upregulation in both CD14+CD16- and CD14+CD16+ subsets than healthy donors. Enhanced polyfunctional strength of monocyte subsets in FTLD patients was mainly driven by IL-8, MIP-1α and MIP-1β.
Increased inflammatory polyfunctional monocyte subsets with unique cytokine signatures provide a potential basis for biomarkers for peripheral immune pathology unique to FTLD, which will be further validated in a larger cohort.