Neutrophil-to-lymphocyte ratio and lymphocyte count reflect alterations in central neurodegeneration-associated proteins and clinical severity in Parkinson Disease patients

Introduction: Peripheral inflammation has been recently associated to Parkinson disease (PD). However, how the peripheral inflammatory immune response could affect the clinical-pathological features of the disease is not fully understood. In this study, we assessed the peripheral immune profile of a well-characterized PD cohort, examining several correlations with CSF biomarkers of neurodegeneration and the main clinical parameters, aimed at better elucidating the complex dynamics of the brain-periphery interactions in PD. Methods: The leukocyte populations counts (neutrophils, lymphocytes, monocytes, eosinophils, and basophils) and the neutrophil-to-lymphocyte ratio (NLR) were collected and compared in 61 PD patients and 60 sex/age matched controls (CTRLs). Immune parameters were correlated with CSF levels of total α-synuclein, amyloid-β-42, total and phosphorylated-tau and main motor and non-motor scores. Results: PD patients had lower lymphocyte and higher NLR counts compared to CTRLs. In PD patients, the lymphocyte count directly correlated with CSF α-synuclein levels, whereas NLR displayed an inverse correlation with the CSF amyloid-β42 levels. The lymphocyte count also negatively correlated with HY stage, while NLR positively with the disease duration. Conclusions: This study provided in vivo evidence that, in PD, changes in leukocytes in the periphery, assessed as relative lymphopenia and NLR increase, reflect in central neurodegeneration-associated proteins modifications, especially in α-synuclein and amyloid-β pathways, and greater clinical burden.