Imbalance of Circulating T17 and Regulatory T Cells in Alzheimer's Disease: A Case Control Study

The neuropathological hallmarks of Alzheimer's disease (AD), i.e., neuritic plaques and neurofibrillary tangles, consist of beta amyloid peptides (Aβ) and hyperphosphorylated Tau. These are accompanied by reactive microglia and astrocytes in the vicinity of the neuritic plaques and by changes to the peripheral immune system, e.g., an increase of the pro-inflammatory cytokines IL-1β, IL-6, and TNF-α in the peripheral blood. To address a potential involvement of peripheral T helper cell (T) subsets in AD, we conducted a case control study with 54 individuals with AD dementia ( = 14), with mild cognitive impairment (MCI) due to AD (MCI,  = 14), with MCI unlikely due to AD (MCI,  = 13), and controls without cognitive impairment (controls,  = 13). The proportions of CD3CD8IL-17AIFNγ Th17 cells, CD3CD8IL-17AIFNγ Th1 cells, and CD4CD127CD25 regulatory T cells (T) were assessed by flow cytometry. In addition, the correlations of the proportions of T subsets to cerebrospinal fluid biomarkers were studied. CD3CD8IL-17AIFNγ Th17 cells were significantly increased in subjects with MCI compared to age- and sex-matched subjects with MCI and controls (MCI mean = 1.13, SD = 0.77; MCI mean = 0.58, SD = 0.28; and controls mean = 0.52, SD = 0.22;  = 0.008). The proportion of CD4CD127CD25 T was not altered between the different groups, but it significantly positively related with the levels of total Tau and pTau181 ( = 0.43,  = 0.021,  = 28;  = 0.46;  = 0.024,  = 28) in subjects with AD but not in nonAD controls (  -0.51,  = 0.007,  = 26). The increase of circulating CD3CD8IL-17AIFNγ Th17 cells in the early stages of AD and the association of CD4CD127CD25 T with neurodegeneration marker Tau may indicate that the adaptive immune system relates to neuropathological changes in AD.