Expression of immune checkpoint on subset of monocytes in old patients.

Background: Immune checkpoints and their ligands are important actors of lymphocytes and monocytes activation's regulation. Their expression level within T cells changes with aging. Despite the major impact of aging on monocytes, there is no data about the expression of ICs on monocytes from old patients. The objective of our study is to describe the expression of ICs and their ligands on monocytes from young individuals compared to old patients.

Methods: We included 18 old control (>75 years old), 10 young control (<55 years old) and 45 old patients with hip fracture (HF). Phenotypical and functional analyses were performed on cryopreserved PBMCs.

Results: There is a differential expression of immune checkpoints and their ligands within monocyte subtypes regardless of age at baseline. After stimulation, a differential expression of immune checkpoints in young subjects but not in old subjects was observed which would be in favor of a regulation defect in old subjects. We hypothesize that this lack of regulation could partially explain the excess production of pro-inflammatory cytokines by the stimulated monocytes in old subjects. In HF, we also observe a differential expression of immune checkpoints, especially in old patients with a poor prognosis.

Conclusion: Our results suggest that the immune regulation which should take place post-acute stress may be affected in old individuals.