Aryl hydrocarbon receptor activation alters immune cell populations in the lung and bone marrow during coronavirus infection.

Respiratory viral infections are one of the major causes of illness and death worldwide. Symptoms associated with respiratory infections can range from mild to severe, and there is limited understanding of why there is large variation in severity. Environmental exposures are a potential causative factor. The aryl hydrocarbon receptor (AHR) is an environment-sensing molecule expressed in all immune cells. Although there is considerable evidence that AHR signaling influences immune responses to other immune challenges, including respiratory pathogens, less is known about the impact of AHR signaling on immune responses during coronavirus (CoV) infection. In this study, we report that AHR activation significantly altered immune cells in the lungs and bone marrow of mice infected with a mouse CoV. AHR activation transiently reduced the frequency of multiple cells in the mononuclear phagocyte system, including monocytes, interstitial macrophages, and dendritic cells in the lung. In the bone marrow, AHR activation altered myelopoiesis, as evidenced by a reduction in granulocyte-monocyte progenitor cells and an increased frequency of myeloid-biased progenitor cells. Moreover, AHR activation significantly affected multiple stages of the megakaryocyte lineage. Overall, these findings indicate that AHR activation modulates multiple aspects of the immune response to a CoV infection. Given the significant burden of respiratory viruses on human health, understanding how environmental exposures shape immune responses to infection advances our knowledge of factors that contribute to variability in disease severity and provides insight into novel approaches to prevent or treat disease.NEW & NOTEWORTHY Our study reveals a multifaceted role for aryl hydrocarbon receptor (AHR) signaling in the immune response to coronavirus (CoV) infection. Sustained AHR activation during in vivo mouse CoV infection altered the frequency of mature immune cells in the lung and modulated emergency hematopoiesis, specifically myelopoiesis and megakaryopoiesis, in bone marrow. This provides new insight into immunoregulation by the AHR and extends our understanding of how environmental exposures can impact host responses to respiratory viral infections.

Post-transplant lymphoproliferative disorder in liver recipients: Characteristics, management, and outcome from a single-centre experience with >1000 liver transplantations.

BACKGROUND: The literature regarding post-transplant lymphoproliferative disorder (PTLD) in liver transplant recipients (LTRs) is limited. OBJECTIVES: To study the incidence, predictors and outcomes of PTLD after liver transplantation in a single, large-volume centre. METHODS: The charts of all LTRs (n=1372) in the authors' centre between January 2000 and June 2012 were retrospectively reviewed and those who developed PTLD were identified. Demographic, clinical and treatment data were prospectively collected. Responses to treatment, including complete response, no response, relapse and survival, were recorded. RESULTS: The incidence of PTLD in LTRs was 32 in 1372 (2.3%). Overall, median survival was 37 months (range 0.5 to 195 months), with one-, three- and five-year survival rates of 81%, 74% and 60%, respectively. Epstein-Barr virus (EBV)-negative patients had a better mean (± SD) survival (95±79 months) than EBV-positive patients (41±42 months) (P=0.02). For stage I/II PTLD, one-, three- and five-year actuarial survival was 87%, 87% and 75%, compared with 50%, 30% and 0% for stage III/IV PTLD, respectively (P=0.001). In patients with complete response, median survival was 58 months (range 10 to 195 months); and one-, three- and five-year actuarial survival was 100%, 94% and 76%, respectively, after diagnosis of PTLD. Changing immunosuppression (IS) from calcineurin inhibitor to sirolimus at the time of diagnosis may have improved survival (seven of seven survivors) compared with only decreasing or stopping IS (14 of 25 survivors) (P=0.07). CONCLUSIONS: This series from a single large-volume centre showed excellent short and long-term survival after PTLD in adult LTRs who were EBV negative, had early disease and showed complete response. Consistent with the known in vitro antiproliferative effect of sirolimus, switching IS from calcineurin inhibitor to sirolimus may improve survival.