Berberine Promotes Induction of Immunological Tolerance to an Allograft via Downregulating Memory CD8+ T-Cells Through Altering the Gut Microbiota

Dysbiosis of the Female Murine Gut Microbiome Exacerbates Neutrophil-Mediated Vascular Allograft Injury by Affecting Immunoregulation by Acetate

BACKGROUND

The gut microbiota affects immune responses that cause organ transplant rejection, but the mechanisms by which this occurs remain poorly understood.

METHODS

We have examined, in a murine model, how disruption of the gut microbiota with antibiotics early in life alters this microbial community later in life to affect immune responses that injure vascular allografts.

RESULTS

Analysis of 16S rRNA and whole genome sequencing of the gut microbiota demonstrated that early life disruption of this microbial community with antibiotics caused a reduction in taxa and enzymatic genes involved in the synthesis of acetate, an immunoregulatory metabolite in mice and humans. When allograft vascular injury was examined, early life disruption of the gut microbiota increased neutrophil accumulation and related medial injury of transplanted arteries. Normalizing the gut microbiota by co-housing and oral administration of acetate prevented neutrophil-mediated vascular allograft injury.

CONCLUSIONS

Dysbiosis of the gut microbiome that reduces its production of the immunoregulatory metabolite acetate exacerbates neutrophil-mediated allograft vascular injury.

Chronic rejection as a persisting phantom menace in organ transplantation: a new hope in the microbiota?

PURPOSE OF REVIEW

The microbiota plays an important role in health and disease. During organ transplantation, perturbations in microbiota influence transplant outcome. We review recent advances in characterizing microbiota and studies on regulation of intestinal epithelial barrier function and mucosal and systemic immunity by microbiota and their metabolites. We discuss implications of these interactions on transplant outcomes.

RECENT FINDINGS

Metagenomic approaches have helped the research community identify beneficial and harmful organisms. Microbiota regulates intestinal epithelial functions. Signals released by epithelial cells or microbiota trigger pro-inflammatory or anti-inflammatory effects on innate and adaptive immune cells, influencing the structure and function of the immune system. Assessment and manipulation of microbiota can be used for biomarkers for diagnosis, prognosis, and therapy.

SUMMARY

The bidirectional dialogue between the microbiota and immune system is a major influence on immunity. It can be targeted for biomarkers or therapy. Recent studies highlight a close association of transplant outcomes with microbiota, suggesting exciting potential avenues for management of host physiology and organ transplantation.

Ablation of Survivin in T Cells Attenuates Acute Allograft Rejection after Murine Heterotopic Heart Transplantation by Inducing Apoptosis

Although studies in oncology have well explored the pharmacological effects of Birc5, little is known about its role in allogeneic T-cell responses. Therefore, the present study used a mouse model of acute heart allograft rejection to investigate the protective effect and mechanism of conditional knockout of Birc5 in T cells. Survivin (encoded by Birc5) was up-regulated in T cells activated in vivo and in vitro. Deletion of Birc5 in T cells attenuated acute heart allograft rejection by reducing the ratio of effector to naive T cells and Th1 to Tregs. In addition, deletion of Birc5 had no noticeable effect on proliferation but on apoptosis and the secretion of IFN-γ. The results revealed a significant increase in the percentage of Annexin V positive CD4⁺ T cells in the Birc5^-/- group, compared to the WT. Moreover, there was significant increase in early apoptotic alloreactive T cells in Birc5^-/- mice and this was partly mediated by caspase-3. Furthermore, treatment with YM155 inhibited acute heart allograft rejection in vivo and increased T-cell apoptosis in healthy human PBMCs in vitro. The results highlight a potential therapeutic target for the prevention and treatment of acute transplant rejection.