“Changes in soluble CD163 indicate monocyte involvement in cognitive deficits in Parkinson’s disease”

Parkinson’s disease is a neurodegenerative disorder with a significant immune component. Numerous studies have reported alterations on immune biomarkers in CSF and serum that associate with symptoms in PD patients. However, it is unclear, which specific immune cells are responsible for the changes in those biomarkers; since most of these cytokines or chemokines, can be produced by a variety of immune cells, or even neurons or glia cells in the brain. Here, we investigate a monocyte/macrophage-specific biomarker: sCD163, the soluble form of the receptor CD163. Our data from tow cohorts show that the CSF-sCD163 increases as the disease progresses, together with a correlated increase in PD-specific as well as neurodegeneration-associated disease biomarkers: alpha-synuclein, tau, and phosphorylated-Tau. Moreover, CSF-sCD163 levels were inversely correlated to the cognitive scores MMSE and MOCA, with higher sCD163 indicating lower cognitive capacity. sCD163 was also increased in serum, although only in female PD patients, suggesting a gender distinctive monocyte-related immune response. CSF-sCD163 also correlated with molecules associated with endothelial cells, tissue infiltration, and activation of B cells and T cells in the PD patients. This suggests activation of both the adaptive and the innate immune system along with recruitment of lymphocytes and monocytes to sites of inflammation in the brain. In serum, sCD163 was associated with pro-inflammatory cytokines and acute phase proteins, suggesting a relation to chronic systemic inflammation. Interestingly, our in vitro study suggests that sCD 163 might enhance alpha-synuclein uptake by myeloid cells without direct binding, thus participating in the clearance of alpha-synuclein. Accordingly, our data supports sCD163 as a potential cognition-related biomarker in PD and corroborates a role for monocytes both in peripheral and brain immune responses that could have direct consequences in the handling of alpha-synuclein.