Interleukin-6 is linked to longitudinal rates of cortical thinning in aging

Interleukin-6 (IL-6) is a pro-inflammatory cytokine produced by immune cells and other cell types such as microglia throughout the brain. Higher levels of IL-6 in older adults have been cross-sectionally and longitudinally associated with physical and cognitive impairment, as well as increased dementia risk. The association between IL-6 levels and structural and functional brain changes is less clear. In the present study, we investigated the relationship between IL-6 concentrations and cortical thinning with aging. Magnetic Resonance Imaging (MRI) scans from the Baltimore Longitudinal Study of Aging were analyzed for 121 older subjects (M = 69.3; SD = 7.3; range = 56.1 - 85.9 yrs) who were repeatedly tested over an average period of 7.5 yrs, and who remained non-demented for the entire follow-up period. The Freesurfer longitudinal processing stream was utilized for image processing, and IL-6 measures were based on serum ELISA assays averaged across time points. Results showed that higher mean IL-6 concentrations were associated with accelerated annual rates of cortical thinning in the inferior temporal poles bilaterally. Additional pronounced regions of IL-6 -accelerated thinning included the transverse frontopolar gyri within the left hemisphere, and subcentral gyrus and sulcus within the right hemisphere. Our results indicate that sustained high levels of the inflammatory biomarker IL-6 are associated with regionally increased rates of age-related cortical thinning. These data build on previous findings that link IL-6 to chronic disease and demonstrate one mechanism through which high levels of inflammation may have adverse effects on physical and cognitive function.