One major organ system associated with aging is our brain and central nervous system. Aging is associated with a shrinkage in brain volume, although the exact cause of this decrease is not definitively known [
5]. The prevailing theories for this observation are neuronal cell death and/or a reduction in neuronal volume [
6]. In addition, changes in the neuronal structure have also been described, such as synaptic pruning [
6], dendritic sprouting [
7], and deterioration of the myelin sheath, which can then affect cognition [
8]. Different areas of the brain exhibit different rates of shrinkage at different ages [
9]. A longitudinal study found that the cross-sectional whole brain, temporal lobe, and hippocampus volumes decreased with age, with an accelerated atrophy rate after 70 years of age [
9]. Multiple cross-sectional studies were also reviewed, and the authors concluded that the prefrontal cortex was the most affected area of the brain with age [
10]. In addition to a decreased brain volume, aging also brings about cognitive decline and pathological diseases. Aging adversely affects the brain vasculature, and the altered blood-brain barrier and reduced cerebral blood flow are associated with white matter lesions, and correspondingly with cognitive decline [
11‐
13]. Hypertension and altered small and large cerebro-vasculature are also associated with stroke and Alzheimer’s disease [
12‐
14]. From an immunological perspective, the aged brain experiences an increase in an inflammatory phenotype. One key cell population proposed to contribute to the inflammation in the brain is the microglia. Microglia is an innate immune cell of the central nervous system, and in aged mouse studies, is primed for increased activation and expression of increased markers of inflammation. Following the theory that increased inflammation in the brain contributes to cognitive decline, cytokines such as type 1 IFN have been shown to negatively impact brain function [
15] while IL-4 is pro-cognitive in mice [
16]. In human studies, peripheral blood CD28− CD4 T cells has been shown to expand in Alzheimer’s patients compared with healthy control, contributing to low-grade inflammation [
17]. Thus, an increased pro-inflammatory phenotype in the central nervous system could be associated with cognitive impairment, which can exacerbate any cognitive degeneration due to age-associated structural changes [
18].