Cerebrospinal fluid levels of IL-6 are decreased and correlate with cognitive status in DLB patients

Malin Wennström, Sara Hall, Katarina Nägga, Elisabet Londos, Lennart Minthon, Oskar Hansson

Inflammatory processes have previously been shown to influence cognition and progression of dementia. An involvement of interleukin (IL)-6 has in particular been suggested as altered levels of IL-6 in cerebrospinal fluid (CSF) have been found in patients with Alzheimer's disease (AD). Also, an association between cognitive decline and levels of IL-6 in CSF have been reported. The aim of the present study was to investigate whether patients clinically diagnosed with dementia with Lewy bodies (DLB) display altered CSF IL-6 levels in comparison with patients with AD and control subjects without dementia and whether the IL-6 levels are correlated with cognitive status and biomarkers for AD and synucleinopathy. To analyse CSF of patients with AD (n = 45), patients with DLB (n = 29) and control subjects without dementia (n = 36), we used immunoassays to measure levels of IL-6 (multiplex electrochemiluminescence); AD markers phosphorylated tau, total tau and amyloid-β1-42 (enzyme-linked immunosorbent assay [ELISA]); and α-synuclein (ELISA). Cognitive status was evaluated using the Mini Mental State Examination (MMSE). Our analysis showed significantly lower levels of IL-6 in CSF from patients with DLB than in CSF from patients with AD and control subjects without dementia. The IL-6 levels were also negatively correlated with MMSE and positively correlated with α-synuclein CSF levels. Our findings support previous studies by demonstrating a link between inflammatory processes and dementia progression and further strengthen the hypothesis that IL-6 is involved in dementia pathology and cognitive decline.