Uncoupling of cytokine signaling and LC3 associated phagocytosis (LAT Akoumianaki1, R Beau2, F Pen drives the development of invasive aspergillosis in patients with sepsis

Author:

T Akoumianaki1, R Beau2, F Pene3, FL van de Veerdonk4, K Vaporidi1, M Netea4,
JP Latge2, G Chamilos1,5

Author address:

1Department of Medicine, University of Crete, Heraklion, Greece
2Unite des Aspergillus, Institute Pasteur, Paris, France
3Medical Intensive Care Unit, Cochin Hospital, Paris, France
4Internal Medicine, Radbout University, Nijmegen, The Netherlands
5Institute of Molecular Biology and Biotechnology, Foundation of Research and Technology, Heraklion, Greece

Full conference title:

9th Advances Against Aspergillosis

Date: 26 February 2020

Abstract:

Purpose: Aspergillus fumigatus is an opportunistic pathogen in a broad range of immunocompromised patients with defects in number or function of phagocytes. In particular, Invasive Aspergillosis (IA) is an emerging infection in critically ill patients recovering from sepsis in the ICU. Defects in cytokine production (e.g., IL-6) by professional phagocytes have been associated with sepsis induced immunoparalysis and increased susceptibility to opportunistic pathogens, including Aspergillus. However, the underlying molecular mechanisms that result in compromised microbicidal activity of phagocytes during sepsis remain uncharacterized. A non-canonical autophagy pathway termed LC3 associated phagocytosis regulates phagolysosomal fusion and confers protective immunity against Aspergillus. In view of the master regulatory role of LAP in phagocyte antifungal immune effector functions, we hypothesized that defective activation of LAP is implicated in sepsis immunosuppression and related susceptibility to IA. Furthermore, we explored molecular mechanisms of cytokine signaling cross talk with LAP that are inhibited in sepsis.

Methods: In a prospective study we evaluated LAP in 38 consecutive adult patients admitted in the ICU of two University Hospitals with community-acquired septic shock. Monocytes isolated on the day of patient admission (day 1) and upon recovery from the infectious episode (day 7) were stimulated with conidia of Aspergillus fumigatus. Cytokines production was measured in culture supernatants by enzyme immunoassay (ELISA). LAP activation and other phagosome responses during fungal infection of monocytes were assessed by confocal microscopy. Functional studies were also performed in a physiologically relevant mouse model of peritonitis (CLP) with different degree of sepsis severity upon re-infection with Aspergillus  by using GFP-LC3 mice, and in Atg5 knockout and IL-6 knockout mice.

Results: We identified a distinct group of patients (n=11, 29%) with defective activation of LAP in monocytes upon sepsis recovery. Defective activation of LAP was associated with impaired phagolysosomal fusion and killing of Aspergillus conidia, cytokine hypo-responsiveness (suppressed IL-6 production), and all hallmark clinical features of sepsis-induced immune deactivation. Studies in the CLP model of polymicrobial sepsis mirrored the findings of human studies by demonstrating selective inhibition of LAP in macrophages of mice recovering from severe sepsis and resulting increased susceptibility to Aspergillus infection. Because of the striking correlation of LAP defects with impaired IL-6 production we explored a direct regulatory role of IL-6 signaling on LAP. Importantly, studies in macrophages from IL-6 KO mice demonstrated LAP blockade, broad phagosome biogenesis defects and defective killing of Aspergillus. Of interest, IL-6 supplementation restored LAP defects and immune deactivation in sepsis monocytes/macrophages.

Conclusion: Our study uncovers a molecular mechanism of sepsis-induced immunosuppression leading to increased susceptibility for IA. In addition, our results provide a novel mechanistic link between defects in molecular pathways regulating IL-6 signaling and phagosome biogenesis in sepsis immunoparalysis.

Abstract Number: 160

Link to conference website:

Link Conference abstract: 

AAAM 2020

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