Original ArticleT regulatory cells activation and distribution are modified in critically ill patients with acute respiratory distress syndrome: A prospective single-centre observational study
Introduction
Acute respiratory distress syndrome (ARDS) is a life-threatening syndrome frequently encountered and a major cause of death in intensive care unit (ICU) [1]. ARDS still concerns 5–20% of patients under mechanical ventilation with a mortality rate of 40–60% [2], [3]. This syndrome is characterised by a dysregulated neutrophil infiltration leading to increased capillary and alveolar permeability. Extensive research testing anti-inflammatory therapies [4] has failed to improve ARDS outcomes.
Aside from neutrophils, other immune cells encompassing lymphocytes are involved in the pathophysiology of ARDS. More specifically, T regulatory cells (Tregs), a subset of CD4 expressing lymphocytes that highly express CD25 [interleukin (IL)-2 receptor α] as well as the transcription factor Forkhead box protein 3 (FoxP3), have been recently demonstrated to play a crucial role in maintaining immune homeostasis [5], [6]. They can suppress inflammatory, allergic, and autoimmune disorders [7] including in pneumonia [8], [9], [10], through contact-dependent suppression or releasing cytokines, e.g. IL-10 and transforming growth factor (TGF)-β1 [6]. Several studies investigated the role of Tregs in either experimental models of acute lung injury or even more rarely in ARDS patients. Most of them yielded conflicting results [10], [11], [12], [13], [14], [15], [16], [17], [18], [19], [20]. In murine models, Tregs have been shown to contribute to the resolution of lung injury [11], [12], [13], [14]. However, recent clinical studies presented Tregs as either a risk factor [10] or a protective factor [20] for mortality. Others yielded inconclusive results [16]. Moreover, their distribution over time between blood and lungs has never been studied in the clinical settings. Similarly, Tregs expression of immunosuppressive markers remains uncovered in patients with ARDS. Finally, phenotyping of T helper (Th) polarisation and innate lymphoid cells (ILCs) populations has been under-studied in ARDS patients [15], [20].
In this context, and since ARDS is characterised by a dysregulated immune response, we hypothesised that either quantitative or functional Tregs impairment may occur over time and could alter outcomes. Thus, we designed this observational longitudinal clinical study to investigate both systemic and bronchoalveolar Tregs phenotype over time, and its potential impact on the mortality of patients with ARDS.
Section snippets
Study design
This prospective observational study was conducted in our 26-bed multidisciplinary ICU from April 2014 to July 2018. The study was approved by the Institutional Ethics Committee Île-de-France VI. Blood and bronchoalveolar lavage (BAL) samples for flow cytometric and cytokines analyses were collected from residual sampling after completion of routine biological and bacteriological follow-up. Because our protocol did not modify usual patient care, the Institutional Review Board waived written
Patients
From April 2014 to July 2018, 105 critically ill patients were included, 60 with and 45 without ARDS criteria. Fig. 2 represents the flow chart of the study. Clinical characteristics of ARDS and non-ARDS patients are reported in the Table 1. Patients with ARDS exhibited higher rate of sepsis, antibiotic use, pneumonia, shock and SOFA score. However, both groups remained with similar simplified acute physiology score and no difference was found between groups regarding cardiovascular,
Discussion
Our main findings are summarised as follows:
- •
ARDS was characterised by an expansion of circulating Tregs whose functional phenotype was altered, an absence of a blood-alveolar gradient in Tregs subset that existed in non-ARDS patients, and a reduction in BAL Tregs, which were paradoxically hyperactivated;
- •
the proportions of blood and BAL Tregs remained stable over time;
- •
blood Tregs/CD4+ percentage < 10.5% within the first week of ARDS was associated with a threefold increase in day-90 mortality.
We
Conclusions
In conclusion, ARDS was characterised by an increase in the pool of blood Tregs exhibiting an activation defect, which potentially hindered their translation within the bronchoalveolar compartment. This led to a quantitative deficit in the pool of alveolar Tregs, and a compensating hyperactivation of the alveolar Tregs and Teffs. Recognition of the role of the modifications of immune phenotypes in initiating and perpetuating lung inflammation may offer new therapeutic opportunities. Increasing
Human and animal rights
The authors declare that the work described has been carried out in accordance with the Declaration of Helsinki of the World Medical Association revised in 2013 for experiments involving humans as well as in accordance with the EU Directive 2010/63/EU for animal experiments.
Informed consent and patient details
The authors declare that this report does not contain any personal information that could lead to the identification of the patient(s).
Disclosure of interest
The authors declare that they have no competing interest.
Funding
Supported by a National Research Contract Grant from the Société française d’anesthésie et de réanimation (Paris, France) (A.M.). This work was also funded by the Agence Nationale pour la Recherche (France) (ANR) within the French government Investissement d’Avenir programme (Labex Transimmunom, ANR-11-IDEX-0004-02).
Author contributions
S.H. contributed to overall study design, performance of the experiments, data analysis and interpretation, and writing of the manuscript. L.A. contributed to the study design, performance of the experiments, and data analysis and interpretation. M.B. contributed to the study design, and performance of the experiments and data analysis. J.-J.R., O.L., H.B. and D.K. contributed to the data analysis and interpretation, and editing of the manuscript. M.R. contributed to the study design, data
Acknowledgements
Not applicable.
References (42)
- et al.
Regulatory T cell migration during an immune response
Trends Immunol
(2012) - et al.
Regulatory T cell compartmentalization and trafficking
Blood
(2006) - et al.
Incidence and outcomes of acute lung injury
N Engl J Med
(2005) - et al.
Recovery and outcomes after the acute respiratory distress syndrome (ARDS) in patients and their family caregivers
Intensive Care Med
(2016) - et al.
Functional disability 5 years after acute respiratory distress syndrome
N Engl J Med
(2011) - et al.
The acute respiratory distress syndrome: from mechanism to translation
J Immunol
(2015) - et al.
Regulatory T cells in nonlymphoid tissues
Nat Immunol
(2013) - et al.
Tregs. Where we are and what comes next?
Front Immunol
(2017) - et al.
Regulatory T cells as immunotherapy
Front Immunol
(2014) - et al.
Regulatory T cells dampen pulmonary inflammation and lung injury in an animal model of pneumocystis pneumonia
J Immunol
(2006)
Immunity and tolerance to Aspergillus involve functionally distinct regulatory T cells and tryptophan catabolism
J Immunol
An increased alveolar CD4 + CD25 + Foxp3 + T regulatory cell ratio in acute respiratory distress syndrome is associated with increased 30-day mortality
Intensive Care Med
Regulatory T cell-mediated resolution of lung injury: identification of potential target genes via expression profiling
Physiol Genomics
Immunological priming requires regulatory T cells and IL-10-producing macrophages to accelerate resolution from severe lung inflammation
J Immunol
CD4 + CD25 + Foxp3+ Tregs resolve experimental lung injury in mice and are present in humans with acute lung injury
J Clin Invest
Regulatory T cells reduce acute lung injury fibroproliferation by decreasing fibrocyte recruitment
Am J Respir Cell Mol Biol
Innate lymphoid cells are the predominant source of IL-17A during the early pathogenesis of acute respiratory distress syndrome
Am J Respir Crit Care Med
Early infectious acute respiratory distress syndrome is characterized by activation and proliferation of alveolar T cells
Eur J Clin Microbiol Infect Dis
T cell subsets in human airways prior to and following endobronchial administration of endotoxin
Respirology
Lymphocytes in the development of lung inflammation: a role for regulatory CD4+ T cells in indirect pulmonary lung injury
J Immunol
BLT1-dependent alveolar recruitment of CD4(+)CD25(+) Foxp3(+) regulatory T cells is important for resolution of acute lung injury
Am J Respir Crit Care Med
Cited by (16)
A digital health platform for assisting the diagnosis and monitoring of COVID-19 progression: An adjuvant approach for augmenting the antiviral response and mitigating the immune-mediated target organ damage
2021, Biomedicine and PharmacotherapyCitation Excerpt :Treg dysfunctions may result from a lack of Treg localization. Some studies have demonstrated that Tregs do not localize to the lung in patients with ARDS and remain in the peripheral blood [85]. The decreased number of Tregs in the blood relative to the proinflammatory Th17 cells was indicated as a marker of ARDS severity [86].
Upregulation of FOXP3 is associated with severity of hypoxia and poor outcomes in COVID-19 patients
2021, VirologyCitation Excerpt :Moreover, the ratio of T regulatory lymphocytes to all CD4+ lymphocytes in the bronchoalveolar lavage (BAL) was found to be an independent prognostic factor for 30-day survival in this study group (Adamzik et al., 2013). Another study showed that blood Tregs/CD4+ percentages were higher in patients who developed ARDS than in those who did not, and that a threshold of 10.4% for the blood Tregs/CD4+ percentages during the first week of ARDS was able to distinguish survivors from non-survivors (Halter et al., 2020). While FOXP3 was generally downregulated in COVID-19, it was upregulated in severe cases, with the development of severe hypoxia.
Luteolin activates Tregs to promote IL-10 expression and alleviating caspase-11-dependent pyroptosis in sepsis-induced lung injury
2021, International ImmunopharmacologyCitation Excerpt :Changes in Tregs activation and distribution in patients with acute respiratory distress syndrome (ARDS). An increase in blood Treg showed a deficiency in activation, which may hinder their translation in the bronchoalveolar chambers [11]. Since Treg homing has been shown to be critical in resolving inflammation response [7,45], the ability of blood Treg homing to ARDS damaged alveoli may be altered.
HMGB1 suppress the expression of IL-35 by regulating Naïve CD4+ T cell differentiation and aggravating Caspase-11-dependent pyroptosis in acute lung injury
2021, International ImmunopharmacologyCitation Excerpt :Treg activation and distribution are modified in critically ill patients with ARDS. An increase in the pool of blood Tregs exhibited an activation defect, which potentially hindered their translation within the bronchoalveolar compartment [37]. In our study, Tregs were undetectable in the lungs.
Gut microbiota and its metabolic products in acute respiratory distress syndrome
2024, Frontiers in Immunology