Lifelong CD8+ T cell deficiency does not ameliorate liver inflammation or alter glucose tolerance in old mice
Authors: Buckley David , Sharma Sunita , Joseph Blessy , Trott Daniel 
Published: May 2023

Previously, we have demonstrated that T cells accumulate in the liver of old animals and that these cells produce inflammatory cytokines. Additionally, we have demonstrated that short term (28d) pharmacological depletion of total (CD3+) and cytotoxic (CD8+) T cells ameliorates this inflammation and results in improved glucose tolerance in old (22-24mo), but not young (4-6mo) mice. We therefore sought to determine if lifelong CD8+ deficiency using a genetic knockout would result in improved glucose tolerance in old mice. We hypothesized that old CD8KO mice would exhibit better glucose tolerance compared to their old T cell intact counterparts due to the amelioration of CD8+ specific inflammation. Young (4-6mo) and old (22-24mo) CD8KO (n=14 Y; 18 O) and C56BL6 (control; n=9 Y; 19 O) of both sexes underwent a glucose tolerance test (GTT) via an i.p. injection (2g/kg) and blood glucose was measured over 2hrs using a handheld glucometer. 24hrs following the GTT, mice were euthanized, and liver T cell number and phenotype was assessed by flow cytometry. Group differences were assessed by two-way ANOVA and Tukey’s post-hoc test. Data shown as mean±SD. Contrary to our hypothesis, there were no effects of age or strain on glucose tolerance (expressed as area under curve (arbitrary units (AU)) young control: 39525±5544 AU, young CD8KO: 39454±12244 AU, old Control: 41245±10733 AU, Old CD8KO:39580±10859 AU). We therefore hypothesized that there may have been accumulation of non-CD8+ T cell populations within the CD8KO livers potentially explaining the lack of GTT strain differences. Within the liver, there was an effect of age, but not strain on total T cell accumulation. Old mice exhibited greater liver CD4+ counts regardless of strain. We found that there was an effect of both age (p=0.0019) and strain (p=0.0167) on liver double negative T cell (CD3+/CD4-/CD8-; DNT) accumulation. Old CD8KO mice exhibited greater DNT accumulation compared to old controls (Control: 131060±97089 cells/g, CD8KO: 283163±211110 cells/g; p=0.03). Additionally, CD8KO mice exhibited age-related accumulation of DNT (young: 98728±94624 cells/g, Old: 283163±211110 cells/g; p=0.0061), while control mice did not exhibit age-related DNT accumulation. Due to this overcompensation of DNTs in the livers of CD8KO mice, we assessed the liver-to-bodyweight ratio, to determine if this overcompensation had any effects on the liver itself. Surprisingly, we found that old CD8KO mice had significantly higher liver-to-body weight ratios compared to the old control mice (Control:0.042±0.006, CD8KO: 0.047±0.005; p=0.0320). These results suggest that old CD8KO mice may have impaired liver function due to the DNT mediated inflammation. Further, accumulation of DNTs may explain why, in contrast to short term CD8+ depletion, lifelong CD8 deficiency does not result in improved glucose tolerance in old mice. Funding: NIH: R01AG060395 K01AG061271 This is the full abstract presented at the American Physiology Summit 2023 meeting and is only available in HTML format. There are no additional versions or additional content available for this abstract. Physiology was not involved in the peer review process.