O2139: Hepatic CD8+ T Cells Correlate with Liver Injury After Massive Small Bowel Resection

Background: Resection-associated liver injury and fibrosis is a detrimental and vexing outcome after massive small bowel resection (SBR). In a murine model, we have shown that liver injury correlates with degree of proximal intestinal resection and is ameliorated by treatment with taurourodeoxycholic acid (TUDCA) or with a distal ileocolic resection (ICR) including the cecum. Altered hepatic innate immune function has been well established in SBR-induced liver injury as well as other forms of livery injury, including non-alcoholic steatohepatitis. We therefore sought to identify whether adaptive immunity is activated in the liver after SBR.

Methods: C57BL/6 mice underwent 50% SBR (n=8), 75% SBR (n=8), 50% SBR with TUDCA treatment (n=10), 50% ICR (n=10), or sham (n=8) operation. Tissues were harvested after 10 weeks. Additional mice underwent sham (n=3) or 75% SBR (n=5) and tissues were harvested after 2 weeks. Adaptive immune cells were identified by immunohistochemical (IHC) staining of CD4 and CD8α in the liver. Gene expression of CD4, NK1.1 and CD8 as well as downstream mediators of cytotoxicity, perforin (Prf1) and Granzyme A (Gzma), was assessed by real-time polymerase chain reaction (RT-PCR). T-tests and ANOVA were used for statistical analyses.

Results: T cell-mediated adaptive immunity was analyzed in samples in which liver injury and fibrosis in response to SBR and mitigation by TUDCA treatment and ICR has been previously demonstrated (Am J Physiol Gastrointest Liver Physiol. 2022;323(3):G165-G176). CD8α positive cells increased incrementally with 50% and 75% SBR compared to sham operation at early and late timepoints as revealed by IHC and RT-PCR (Figure 1A-B,D). CD4 positive cells also increased after 50% and 75% SBR (Figure 1C-D); however, only CD8α+ cells were diminished after ICR or TUDCA treatment after SBR (Figure 1B,D). Additionally, hepatic expression of downstream mediators of cytotoxicity, Prf1 and Gzma, was increased 10 weeks after 75% SBR compared to sham operation, indicating an active cytotoxicity in the liver in response to SBR (Figure 1E). Finally, given that natural killer (NK) cells and cytotoxic T lymphocytes both express CD8α, we considered the possibility that the observed signal might arise from increased NK cells. Gene expression of NK1.1, a marker expressed on NK cells in C57BL/6 mice, was measured and no difference was detected between sham and 75% SBR, suggesting that elevation in CD8α+ T cells is likely responsible for the increased cytotoxicity and liver injury after massive small bowel resection.

Conclusion: Liver injury after massive SBR is associated with increased CD8+ T cells and downstream mediators of cytotoxicity in the liver, suggesting a role for adaptive immunity in the disease process. Further investigation of the function of different CD4+ and CD8+ subgroups is underway to determine if such alterations in T cell-mediated adaptive immunity could drive liver injury after SBR.