Innate Immune Response During Community Acquired Pneumonia

- Clinical and scientific background:

Community acquired pneumonia is a major cause of morbidity and mortality worldwide. Despite recent improvement in acute management (specifically for administration of antibiotics), severe pneumonia can worsen and ultimately progressing to Acute Respiratory Distress Syndrome (ARDS), a clinical entity with an inacceptable 40% hospital mortality. From a pathophysiological point of view, ARDS is characterized by a deregulation of pulmonary inflammation initially triggered by the local aggression, which is, in two-third of the cases, a pneumonia. Alteration of tissue repair is another major characteristic of this entity. So far, the scientific knowledge on this pathophysiology did not translate into specific therapy that could modulate efficiently the inflammatory response and to control the progression from pneumonia to ARDS, and/or to improve tissue repair. Thus, a complete reconsideration of the pathophysiological mechanisms is mandatory. Recent progresses in mucosal biology and innate immunity give interesting new opportunities. Specifically, recently discovered unconventional T cells have shown to be major actors in shaping and modulating early immune responses in the lung mucosa during microbial aggressions and for secondary tissue repair. However, these evidences are limited to pre-clinical models. In many other human diseases (oncology, immune diseases), these sub-populations are already being explored as potential targets for immune therapies.

- Objective of the study:

The aim of this study is to explore potential implications of unconventional T cells during human severe pneumonia and ARDS.

This translational study will complement experimental approaches currently undertaken in the laboratory exploring the role of unconventional T cells in murine models of severe pneumonia and ARDS.

- Design:

This is a prospective single-center study including participants admitted in Intensive Care Department of the university hospital of Tours for community-acquired pneumonia. Given the exploratory nature of the study, we designed a "control" group of participants admitted to ICU without evident signs of pneumonia and shock.

Number of participants: 300 for "pneumonia" group, and 50 for "control" group

- Interventions and analysis:

Blood samples will be collected at inclusion, day 3, 8 and 15 during patient's stay in ICU. For mechanically ventilated participants, tracheal aspirates will be also collected at the same timing. If available, broncho-alveolar lavages will be also collected. If ARDS or Ventilator Associated Pneumonia (VAP) are subsequently diagnosed, supplemental blood and tracheal aspirates samples will be collected.

Blood samples and airway fluid samples will be treated to perform flow cytometry analysis for immunophenotypage (cellular content). In some cases, intra-cellular staining will be performed to assess cytokine production and/or transcription factor expression. Functions of unconventional T cells will also be performed after ex vivo stimulation on purified population (cell sorting). Cytokine level sand transcriptomic analyses will also be performed on blood samples.

Clinical characteristics (including respiratory parameters, blood gas, organ dysfunctions, survival at day 28 and day 90) will also be collected. Thus, frequency, activation status and functions of unconventional T cells will be dynamically analyzed in regard of clinical evolution within-individuals and across pneumonia vs control groups. A particular focus will be made on respiratory parameters (ventilation mode, and for participants with ARDS, P/F ratio, driving pressure), organ dysfunctions (as measured by SOFA score), and microbial documentation of the pneumonia.

Moreover, participants treated for ARDS are usually followed in a post-ICU follow-up clinic program in the ICU where the research is conducted. Thus, investigators will perform analysis of the unconventional T cell compartment (blood samples) in the participants firstly enrolled in the study. This will allow exploration of long-term imprinting on the innate immune response after the initial trigger.