D. A. Harris1, R. Subramaniam1, K. Heshmati1, A. Tavakkoli1, E. Sheu1 1Brigham And Women’s Hospital,General Surgery,Boston, MA, USA
Introduction: Obesity is associated with chronic inflammation driven in part by disruption in intestinal immune integrity leading to insulin resistance. Sleeve gastrectomy (SG) is the most performed bariatric surgery in the US, but its mechanisms remain incompletely defined. We hypothesized that SG improves glucose metabolism through normalization of obesity-induced immune dysregulation.
Methods: C57Bl/6J mice were placed into four groups – normal chow diet (lean; n=6); high fat diet (Obese; n=6); Obese Sham (n=7); Obese SG (n=6). Glucose tolerance, insulin tolerance, and immune phenotype were measured through 6 weeks. Liver, jejunum, and spleen were harvested for time of flight mass cytometry (CyTOF), which is a novel platform allowing quantitative immune profiling. A 24-antibody panel directed against key markers of innate and adaptive lymphocytes was developed. Visualization of stochastic neighbor embedding (ViSNE) was used for unbiased profiling.
Results: Obese mice weighed more (40.7±2.4 vs 27.9±2.7g; p<0.001) and had worse fasting glycemia (139±14 vs 99±3 mg/dL; p<0.001) compared to Lean mice. CyTOF was used to compare splenic, hepatic, and jejunal immune populations in these groups. Obese mice have organ-specific perturbations of multiple immune populations compared to Lean mice such as changes in splenic B-cells, hepatic CD4+ TH1 cells, and jejunal CD8+CD103+ tissue resident memory (TRM) T-cells (p<0.05).
Obese SG mice exhibited significant weight loss, improved oral glucose tolerance (AUC, Obese Sham: 34693 [30338 to 39048], Obese SG: 25630 [21984 to 29257]), and increased insulin sensitivity (p<0.05 at 0, 15, 30 mins) compared to Obese Sham mice. Again, CyTOF was used to evaluate the impact of SG on splenic, hepatic, and jejunal immunity. Of the 40 distinct lymphocyte populations assessed, ViSNE revealed that only changes in jejunal CD8+CD103+ TRM correlated with improved weight and insulin sensitivity following SG (Figure 1A). TRM are responsible for rapid pathogen defense at mucosal surfaces. Obese mice have reduced jejunal TRM compared to Lean mice (85.2±7 vs 36.8±10, p=0.003, Figure 1B). SG repairs this obesity-induced mucosal immune defect by restoring jejunal TRM to levels seen in healthy, Lean mice (Figure 1B), a finding validated by flow cytometry. Changes in TRM were confined to jejunum and not seen in the liver or spleen.
Conclusion: Obesity is associated with a disruption in intestinal immunity leading to insulin resistance. SG reverses the deficit in jejunal TRM cells seen in obesity and thereby restores protective intestinal immune function, which may contribute to its metabolic benefits.
