Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) are a continuum of lung changes arising from a wide variety of lung injuries, frequently resulting in significant morbidity and frequently in death. Research regarding the molecular pathophysiology of ALI/ARDS is ongoing, with the aim toward developing prognostic molecular biomarkers and molecular-based therapy.Context.—

To review the clinical, radiologic, and pathologic features of ALI/ARDS; and the molecular pathophysiology of ALI/ARDS, with consideration of possible predictive/prognostic molecular biomarkers and possible molecular-based therapies.Objective.—

Examination of the English-language medical literature regarding ALI and ARDS.Data Sources.—

ARDS is primarily a clinicoradiologic diagnosis; however, lung biopsy plays an important diagnostic role in certain cases. A significant amount of progress has been made in the elucidation of ARDS pathophysiology and in predicting patient response, however, currently there is no viable predictive molecular biomarkers for predicting the severity of ARDS, or molecular-based ARDS therapies. The proinflammatory cytokines TNF-α (tumor necrosis factor α), interleukin (IL)–1β, IL-6, IL-8, and IL-18 are among the most promising as biomarkers for predicting morbidity and mortality.Conclusions.—

First officially described in 1967,1  acute respiratory distress syndrome (ARDS) is a complex and cascading process developing from acute lung injury (ALI). It has multiple etiologies and often results in fulminant respiratory failure and death. Approximately 150 000 individuals receive a diagnosis of ARDS in the United States each year. Currently, treatment is primarily supportive and focused on treatment of the underlying condition and bedside care, including mechanical ventilation2  and corticosteroid administration. Much of the current research into ARDS pathogenesis and treatment is concentrated on identifying causative and prognostically important plasma and molecular biomarkers involved in the development of ALI and the progression of ALI to ARDS, with an aim toward diagnosing ALI in patients before ARDS develops. Because most cases develop within 2 to 5 days of hospitalization,3  efforts to develop molecular-based therapies that interrupt the progression of ALI to ARDS is an attractive endeavor.4  This article reviews ALI/ARDS, including current research in the molecular aspects and pathogenesis of ALI/ARDS.

HISTORY AND DEFINITIONS

The first description of ALI/ARDS, albeit not termed as such, was probably from a physician serving with the Canadian Forces in 19155 in describing a soldier with “shock lung” due to exposure to poison gas.6  In 1967, Ashbaugh et al1  coined the now well-known term acute respiratory distress syndrome to describe a clinical syndrome characterized by “an acute onset of tachypnea, hypoxaemia, and loss of compliance after a variety of stimuli.” In 1994, the American-European Consensus Conferences (AECC) on ARDS published a statement on definitions, mechanisms, relevant outcomes, and clinical trial coordination7  that attempted to delineate and guide treatment; however, there remained some confusion due to overlapping criteria applied to the definition of ALI and ARDS, specifically in relation to hypoxia levels and imaging interpretation. In 2012, the Berlin definition of ARDS was published, emphasizing 3 categories of ARDS—mild, moderate, and severe—based on the degree of hypoxemia.8  It provided superior predictive validity for mortality in comparison to the AECC definitions.8  According to the Berlin definition, ARDS is defined by an acute hypoxemia, a ratio of partial pressure of atrial oxygen to the fraction of inspired oxygen less than or equal to 300 mm Hg on positive end-expiratory pressure greater than or equal to 5 cm H2O, together with bilateral infiltration on radiology that is not otherwise explained fully by fluid overload or cardiac failure.8  In 2015, Riviello et al,9  concerned that the Berlin definition underestimates ARDS incidence in low-income countries, suggested a further definition, termed the Kigali modification, attempting to define ARDS without access to imaging or advanced testing modalities. ARDS incidence may indeed be underestimated; it varies widely depending on the definition used and the strictness of adherence to the current Berlin criteria.

The causes of ALI/ARDS are legion, and include, but are not limited to, infection, collagen vascular diseases, drug effects, ingestants, inhalants, shock, acute eosinophilic pneumonia, immunologically mediated pulmonary hemorrhage and vasculitis, and radiation pneumonitis. The term acute interstitial pneumonia, also termed Hamman-Rich syndrome, describes cases of diffuse alveolar damage (DAD) that are idiopathic. ARDS mortality has remained at approximately 40% for the past 2 decades.10 

RADIOLOGY

ARDS is typically a diagnosis based on clinical and radiologic features. Radiologically, the early exudative phase shows bilateral and patchy ground-glass densities, corresponding to interstitial edema and hyaline membranes. The geographic distribution of the patchy ground-glass densities, together with areas of lobular sparing and lower lobe consolidation, serve as radiologic hallmarks.11  Radiologic features of disease advancement to the proliferative and fibrotic phases are characterized by traction bronchiolectasis or bronchiectasis within areas of increased attenuation on high-resolution computerized tomography scans.12 

PATHOLOGY

Because most ARDS cases are diagnosed clinicoradiographically, biopsies are uncommonly required for diagnosis. Biopsies typically are performed in cases where presentation is not straightforward, specific infection is being considered, or therapeutic response is disappointing.

Diffuse alveolar damage, the histologic counterpart of ALI/ARDS, occurs as the culmination of the cascading process of ALI, developing from epithelial barrier dysfunction, endothelial dysfunction, and resultant pulmonary edema. As described by Katzenstein,13  DAD can be divided into 3 phases: acute/early or exudative, organizing or proliferative, and late-resolving or fibrotic phase. The acute phase is characterized by distinctive hyaline membranes lining alveolar spaces (Figure 1). Edema is frequently identified and acute alveolar hemorrhage may be present. Endothelial cells and pneumocytes undergo necrosis. The hyaline membranes begin to organize as DAD continues into the organizing phase, and granulation tissue develops in the alveolar spaces. Type II pneumocytes demonstrate marked reactivity and become hyperplastic near the end of the early phase. These features can continue through the proliferative phase (Figure 2). Squamous metaplasia, occasionally exuberant enough to mimic carcinoma, may arise (Figure 3). As the organizing phase progresses, granulation tissue is incorporated into the alveolar septa, leading to organizing fibrosis (Figure 4). In the late-resolving or fibrotic phase there is dense collagen fibrosis and hyalinization of the alveolar walls.1315  The stages occur in a continuum rather than in a strict chronologic fashion. Continuing ALI may occur, with the biopsy specimen showing acute and organizing phases simultaneously. For patients who survive ARDS, many cases resolve with minimal lung damage; however, patients may develop varying degrees of end-stage lung change.

Figure 1.

Early exudative stage with hyaline membranes outlining alveolar spaces and mild interstitial edema (hematoxylin-eosin, original magnification ×200).

Figure 2.Late exudative/proliferative phase with prominent type II cells and mitotic figures (hematoxylin-eosin, original magnification ×200).

Figure 3.Prominent squamous metaplasia (hematoxylin-eosin, original magnification ×200).

Figure 4.Late proliferative phase demonstrating organizing pneumonia–like air space organization (hematoxylin-eosin, original magnification ×200).

Figure 1.

Early exudative stage with hyaline membranes outlining alveolar spaces and mild interstitial edema (hematoxylin-eosin, original magnification ×200).

Figure 2.Late exudative/proliferative phase with prominent type II cells and mitotic figures (hematoxylin-eosin, original magnification ×200).

Figure 3.Prominent squamous metaplasia (hematoxylin-eosin, original magnification ×200).

Figure 4.Late proliferative phase demonstrating organizing pneumonia–like air space organization (hematoxylin-eosin, original magnification ×200).

An additional histologic pattern of ALI/ARDS, acute fibrinous and organizing pneumonia (AFOP), is characterized by patchy areas of eosinophilic fibrin aggregates or balls within intraalveolar spaces. AFOP can be seen as a predominant pattern or a component of a DAD. Diagnosis should be based on the predominant feature. Cases demonstrating a primarily AFOP pattern with minimal or no hyaline membranes have shown a worse prognosis.16 

MOLECULAR INVESTIGATION INTO THE PATHOPHYSIOLOGY OF ARDS

Innate Immunity and ARDS

Much research is being performed in an attempt to elucidate the intricacies of the process of ALI development and progression of ALI to ARDS.17  One of the emerging concepts in immunology as applied to the development of ARDS is pattern recognition receptors (PRRs)—critical components of the innate immune system that serve as a “first line of defense.” Pattern recognition receptors recognize 2 categories of ligands: nonendogenous pathogen-associated molecular patterns (PAMPs), and endogenous danger (or damage)–associated molecular patterns (DAMPs). Pattern recognition receptors can initiate inflammatory signaling cascades and the release of proinflammatory cytokines such as tumor necrosis factor α (TNF-α), interleukin (IL)–1β, and IL-8; stimulate autophagy or apoptosis; and induce production of antibacterial molecules.18  Ten functional Toll-like receptors (TLRs), transmembrane PRRs that are highly conserved in vertebrates, have been identified in human beings.19,20  Nucleotide-binding oligomerization domain–like receptors (NLRs) are cytosolic PRRs.21  The NLRs are expressed on both white blood cells and epithelial cells, both of which are in contact with invading microorganisms. Examples of DAMPs include histones and high-mobility group box 1, as contrasted with PAMPs, which include lipopolysaccharides and lipoteichoic acid. In murine studies, TLR signaling pathways have been shown to be involved not only in ARDS development, but also in its resolution.22  For example, degradation products of hyaluronan, an extracellular matrix glucosaminoglycan produced after tissue injury, interact with TLR4 and TLR2 to induce inflammatory responses leading the ALI.22  It has also been shown that overexpression of high-molecular mass hyaluronan in lung epithelial cells is protective against lung injury and apoptosis.22  Other important products of cellular injury are mitochondrial DAMPs, which include cardiolipin, formyl peptides, and mitochondrial DNA.23,24  Mitochondrial DAMPs have been shown to be involved with ARDS in several ways, the foremost being their ability to activate neutrophils by inducing production of the powerful neutrophil attractor and activator IL-8.25  Interleukin 8 forms complexes with anti–IL-8 neutralizing autoantibodies, which in turn interact with FcγRII receptors that then affect neutrophil apoptosis.25  In addition, increased plasma levels of mitochondrial DAMPs are associated with higher mortality rates.25  Studies26  have shown that circulating mitochondrial DAMPs can cause neutrophil-mediated tissue damage.

Neutrophils and ARDS

ALI/ARDS severity and possibly development is greatly influenced by neutrophil migration into the lungs in response to activated alveolar macrophages.27  In the lung, activated neutrophils produce numerous cytotoxic substances, including granular enzymes, reactive oxygen species, bioactive lipids, various proinflammatory cytokines, and neutrophil extracellular traps (NETs), which trap pathogens in the extracellular space through NETosis.28  NETs are cleared slowly from the lungs owing to the lower levels of surfactant proteins A and D, which are required for clearing NETs, in patients with ARDS.28  Regardless of the inciting molecule or molecules, complement activation ensues and is critical for ALI/ARDS development.29 

ARDS Biomarkers

The 2012 Berlin definition of ALI/ARDS did not recommend any biomarkers, and currently there are few markers actively used in clinical practice.30  Brain natriuretic peptide is used to distinguish hydrostatic pulmonary edema from edema due to ARDS, however, its use is controversial.30,31  Procalcitonin has been suggested for use in differentiating bacterial pneumonia from ARDS, but its relatively low sensitivity (approximately 70%) for bacterial pneumonia—itself an etiology of ARDS—makes its use problematic.32  There are no currently clinically useful molecular biomarkers for predicting ARDS severity; however, the PaO2/FiO2 ratio (partial pressure of alveolar oxygen/fraction of inspired oxygen) is used clinically to predict severity.8

Potential Molecular Biomarkers for ARDS

Several potential biomarkers exist in plasma or bronchoalveolar lavage (BAL) specimens, many of which are currently being actively researched in animal studies; however, these have generally failed to show significant results in early human clinical trials. Among the proinflammatory cytokines, TNF-α, IL-1β, IL-6, IL-8, and IL-18 are the most promising potential molecular biomarkers for predicting morbidity and mortality (Table).

Selected Potential Biomarkers for Acute Respiratory Distress Syndrome

Selected Potential Biomarkers for Acute Respiratory Distress Syndrome
Selected Potential Biomarkers for Acute Respiratory Distress Syndrome

Interleukin 18 has promise as a molecular biomarker for prognosis prediction. Dolinay et al,33  studying 217 patients with trauma- or sepsis-induced ARDS, found that increased IL-18 levels correlated with increased in-hospital mortality. Interleukin 18 and IL-1β are activated by caspase-1, which cleaves them from their proforms. Caspase-1, a proinflammatory cytokine belonging to the IL-1 cytokine family, is itself activated by an inflammasome, an intracellular macromolecular complex.34,35  Inflammasomes, of which many are now recognized, respond to TLRs, bacterial- and viral-derived molecules, particle irritants, and reactive oxygen species from neutrophils or mitochondria, gram-negative bacteria, and DNA.3644  The caspase-1 pathway is integral in the acute inflammatory response.

Interleukin 8 in particular deserves note, especially in regard to its association with neutrophils. Interleukin 8 concentrations in BAL fluid are higher in patients with ARDS and, as previously mentioned, attract and activate neutrophils.45,46  Interleukin 8 forms complexes—demonstrated in BAL fluids of patients with ARDS—with anti–IL-8 autoantibodies, which in turn affect interactions of IL-8 with neutrophils.46  These complexes have been shown to activate and chemoattract neutrophils as well as prolong neutrophil life by inhibiting apoptosis through engagement of FcγRIIa.45,46  Also, clinical disease activity is correlated with anti–IL-8:IL-8 concentrations in BAL fluids.47  There is a significant correlation between the onset of ARDS and the concentration of anti–IL-8:IL-8 complexes.46,47  The concentration may also serve as a marker of mortality, as complex concentrations were found to be higher on day 1 of ARDS onset in patients who died of disease, as compared with those who survived.48,49  It is likely that the high levels of these complexes in the lung overwhelm removal mechanisms, and further contribute to neutrophil concentrations and activation, thus contributing to the ongoing damage occurring in ALI/ARDS.

A recent meta-analysis by Terpstra et al50  (reviewing 54 studies comprising 3753 patients) of the performance of 20 potential plasma biomarkers found that IL-4, IL-2, angiopoietin-2, Krebs von den Lungen-6, and protein C (decreased levels) showed the strongest associations with mortality in patients with ARDS.

Growth Factors as Candidate Molecular ARDS Biomarkers

Vascular endothelial growth factor (VEGF) concentrations have been studied in lung endothelial lining fluid in a small cohort of patients and are inversely correlated with lung injury; it is hypothesized that upregulation of VEGF production contributes to decreasing inflammation and is correlated with improved outcomes.51  A study of 32 patients with ARDS measured the levels of alveolar type II epithelial cell growth factors, hepatocyte growth factor, and keratinocyte growth factor, and found that keratinocyte growth factor in BAL fluids of patients with ARDS correlated with a poorer prognosis.52  However, hepatocyte growth factor, while elevated in patients who did poorly, was identified in most BAL specimens, including control samples.52 

EFFECTIVE TREATMENTS

Treatment is generally supportive, with emphasis on treating the underlying cause of disease. One clinical intervention to have shown benefit was observed in a phase III trial, demonstrating a modest but significant decrease in mortality with lower tidal volumes (initially 6 mL/kg of predicted body weight with a plateau pressure of 30 cm H2O or less).2  The lower volumes also served to increase the number of ventilator-free days.2 

CONCLUSIONS

Current presumed molecular pathways leading to ALI/ARDS initially involve complement activation potentially induced by a variety of inflammatory insults (such as sepsis, pneumonia, traumatic injury, blood transfusions, or mitochondrial DAMPs). Alveolar macrophages are activated via TLR and NLR signaling pathways that lead to further macrophage and circulating neutrophil recruitment. Neutrophils accumulate in the lungs and release proinflammatory cytokines and NETs. The lung epithelium, specifically type II alveolar cells, is damaged by these cells and their products, with resultant disruption of the alveolar-capillary interface and increased pulmonary microvascular permeability. The resulting pulmonary edema impairs gas exchange, which in some cases may lead to respiratory failure. And ARDS is not an isolated pulmonary process; the release of oxidants and proteases from the activated neutrophils and macrophages can also cause distant tissue and organ damage and dysfunction.53 

While a significant amount of research has been done in an attempt to understand ALI/ARDS pathophysiology, the development of viable predictive molecular biomarkers and molecular-based therapies remains elusive. Yet, a significant amount of progress has been made in the elucidation of ARDS pathophysiology and in predicting patient response. As Kress54  states, we still measure mortality as our main outcome in clinical trials in ARDS, but now it is time to begin focusing on function and quality of life in survivors of ARDS.

References

References
1.
Ashbaugh
DG,
Bigelow
DB,
Petty
TL,
Levine
BE.
Acute respiratory distress in adults
.
Lancet
.
1967
;
2
(
7511
):
319
323
.
2.
The Acute Respiratory Distress Syndrome Network
.
Ventilation with lower tidal volumes as compared with traditional tidal volumes for acute lung injury and the acute respiratory distress syndrome
.
N Engl J Med
.
2000
;
342
(
18
):
1301
1308
.
3.
Gajic
O,
Dabbagh
O,
Park
PK,
et al.
Early identification of patients at risk of acute lung injury: evaluation of lung injury prediction score in a multicenter cohort study
.
Am J Respir Crit Care Med
.
2011
;
183
(
4
):
462
470
.
4.
Ruthman
CA,
Festic
E.
Emerging therapies for the prevention of acute respiratory distress syndrome
.
Ther Adv Respir Dis
.
2015
;
9
(
4
):
173
187
.
5.
Sloggett
AT,
ed
.
Memorandum of the Treatment of Injuries in War
.
London, England
:
Harrison and Sons;
1915
:
115
122
.
6.
Montgomery
AB.
Early description of ARDS
.
Chest
.
1991
;
99
(
1
):
261
262
.
7.
Bernard
GR,
Artigas
A,
Brigham
KL,
et al.
The American-European Consensus Conference on ARDS: definitions, mechanisms, relevant outcomes, and clinical trial coordination
.
Am J Respir Crit Care Med
.
1994
;
149
(
3, pt 1
):
818
824
.
8.
ARDS Definition Task Force
,
Ranieri
VM,
Rubenfeld
GD,
et al.
Acute respiratory distress syndrome: the Berlin definition
.
JAMA
.
2012
;
307
(
23
):
2526
2533
.
9.
Riviello
ED,
Kiviri
W,
Twagirumugabe
T,
et al.
Hospital incidence and outcomes of ARDS using the Kigali modification of the Berlin definition
.
Am J Respir Crit Care Med
.
2016
;
193
(
1
):
52
59
.
10.
Phua
J,
Badia
JR,
Adhikari
NK,
et al.
Has mortality from acute respiratory distress syndrome decreased over time: a systematic review
.
Am J Respir Crit Care Med
.
2009
;
179
(
3
):
220
227
.
11.
Zompatori
M,
Ciccarese
F,
Fasano
L.
Overview of current lung imaging in acute respiratory distress syndrome
.
Eur Respir Rev
.
2014
;
23
(
134
):
519
530
.
12.
Ichikado
K.
High-resolution computed tomography findings of acute respiratory distress syndrome, acute interstitial pneumonia, and acute exacerbation of idiopathic pulmonary fibrosis
.
Semin Ultrasound CT MR
.
2014
;
35
(
1
):
39
46
.
13.
Katzenstein
AL.
Acute lung injury patterns: diffuse alveolar damage and bronchiolitis obliterans organizing pneumonia
.
In
:
Katzenstein and Askin's Surgical Pathology of Non-Neoplastic Lung Disease. 4th ed
.
Philadelphia, PA
:
Saunders Elsevier;
2006
:
17
50
.
14.
Katzenstein
AL,
Myers
JL,
Mazur
MT.
Acute interstitial pneumonia: a clinicopathologic, ultrastructural, and cell kinetic study
.
Am J Surg Pathol
.
1986
;
10
(
4
):
256
267
.
15.
Katzenstein
A,
Askin
F,
eds
.
Katzenstein and Askin's Surgical Pathology of Non-Neoplastic Lung Disease. 3rd ed
.
Philadelphia, PA
:
Saunders;
1997
.
16.
Beasley
MB,
Franks
TJ,
Galvin
JR,
Gochuico
B,
Travis
WD.
Acute fibrinous and organizing pneumonia: a histological pattern of lung injury and possible variant of diffuse alveolar damage
.
Arch Pathol Lab Med
.
2002
;
126
(
9
):
1064
1070
.
17.
Rubenfeld
GD,
Caldwell
E,
Peabody
E,
et al.
Incidence and outcomes of acute lung injury
.
N Engl J Med
.
2005
;
353
(
16
):
1685
1693
.
18.
Takeuchi
O,
Akira
S.
Pattern recognition receptors and inflammation
.
Cell
.
2010
;
140
(
6
):
805
820
.
19.
Rock
FL,
Hardiman
G,
Timans
JC,
Kastelein
RA,
Bazan
JF.
A family of human receptors structurally related to Drosophila Toll
.
Proc Natl Acad Sci U S A
.
1998
;
95
(
2
):
588
593
.
20.
Kawai
T,
Akira
S.
The role of pattern-recognition receptors in innate immunity: update on Toll-like receptors
.
Nat Immunol
.
2010
;
11
(
5
):
373
384
.
21.
Leissinger
M,
Kulkarni
R,
Zemans
RL,
Downey
GP,
Jeyaseelan
S.
Investigating the role of nucleotide-binding oligomerization domain-like receptors in bacterial lung infection
.
Am J Respir Crit Care Med
.
2014
;
189
(
12
):
1461
1468
.
22.
Jiang
D,
Liang
J,
Fan
J,
et al.
Regulation of lung injury and repair by Toll-like receptors and hyaluronan
.
Nat Med
.
2005
;
11
(
11
):
1173
1179
.
23.
Zhang
Q,
Raoof
M,
Chen
Y,
et al.
Circulating mitochondrial DAMPs cause inflammatory responses to injury
.
Nature
.
2010
;
464
(
7285
):
104
107
.
24.
Ray
NB,
Durairaj
L,
Chen
BB,
et al.
Dynamic regulation of cardiolipin by the lipid pump Atp8b1 determines the severity of lung injury in experimental pneumonia
.
Nat Med
.
2010
;
16
(
10
):
1120
1127
.
25.
Simmons
JD,
Lee
YL,
Mulekar
S,
et al.
Elevated levels of plasma mitochondrial DNA DAMPs are linked to clinical outcome in severely injured human subjects
[discussion in
Ann Surg
.
2013
;
258
(
4
):
596
598
]. Ann Surg. 2013;
258
(
4
):
591
596
.
26.
Sun
S,
Sursal
T,
Adibnia
Y,
et al.
Mitochondrial DAMPs increase endothelial permeability through neutrophil dependent and independent pathways
.
PLoS One
.
2013
;
8
(
3
):
e59989
.
27.
Williams
AE,
Chambers
RC.
The mercurial nature of neutrophils: still an enigma in ARDS?
Am J Physiol Lung Cell Mol Physiol
.
2014
;
306
(
3
):
L217
L230
.
28.
Douda
DN,
Jackson
R,
Grasemann
H,
Palaniyar
N.
Innate immune collectin surfactant protein D simultaneously binds both neutrophil extracellular traps and carbohydrate ligands and promotes bacterial trapping
.
J Immunol
.
2011
;
187
(
4
):
1856
1865
.
29.
Bosmann
M,
Ward
PA.
Role of C3, C5 and anaphylatoxin receptors in acute lung injury and in sepsis
.
Adv Exp Med Biol
.
2012
;
946
:
147
159
.
30.
Levitt
JE,
Vinayak
AG,
Gehlbach
BK,
et al.
Diagnostic utility of B-type natriuretic peptide in critically ill patients with pulmonary edema: a prospective cohort study
.
Crit Care
.
2008
;
12
(
1
):
R3
.
31.
Rana
R,
Vlahakis
NE,
Daniels
CE,
et al.
B-type natriuretic peptide in the assessment of acute lung injury and cardiogenic pulmonary edema
.
Crit Care Med
.
2006
;
34
(
7
):
1941
1946
.
32.
Luyt
CE,
Combes
A,
Reynaud
C,
et al.
Usefulness of procalcitonin for the diagnosis of ventilator-associated pneumonia
.
Intensive Care Med
.
2008
;
34
(
8
):
1434
1440
.
33.
Dolinay
T,
Kim
YS,
Howrylak
J,
et al.
Inflammasome-regulated cytokines are critical mediators of acute lung injury
.
Am J Respir Crit Care Med
.
2012
;
185
(
11
):
1225
1234
.
34.
Schroder
K,
Tschopp
J.
The inflammasomes
.
Cell
.
2010
;
140
(
6
):
821
832
.
35.
Ichinohe
T,
Lee
HK,
Ogura
Y,
Flavell
R,
Iwasaki
A.
Inflammasome recognition of influenza virus is essential for adaptive immune responses
.
J Exp Med
.
2009
;
206
(
1
):
79
87
.
36.
Andrei
C,
Margiocco
P,
Poggi
A,
Lotti
LV,
Torrisi
MR,
Rubartelli
A.
Phospholipases
C
and A2 control lysosome-mediated IL-1 beta secretion: implications for inflammatory processes
.
Proc Natl Acad Sci U S A
.
2004
;
101
(
26
):
9745
9750
.
37.
Mariathasan
S,
Weiss
DS,
Newton
K,
et al.
Cryopyrin activates the inflammasome in response to toxins and ATP
.
Nature
.
2006
;
440
(
7081
):
228
232
.
38.
Franchi
L,
Eigenbrod
T,
Muñoz-Planillo
R,
Nuñez
G.
The inflammasome: a caspase-1-activation platform that regulates immune responses and disease pathogenesis
.
Nat Immunol
.
2009
;
10
(
3
):
241
247
.
39.
Lamkanfi
M,
Dixit
VM.
Modulation of inflammasome pathways by bacterial and viral pathogens
.
J Immunol
.
2010
;
187
(
2
):
597
602
.
40.
Hornung
V,
Bauernfeind
F,
Halle
A,
et al.
Silica crystals and aluminum salts activate the nalp3 inflammasome through phagosomal destabilization
.
Nat Immunol
.
2008
;
9
(
8
):
847
856
.
41.
Martinon
F,
Petrilli
V,
Mayor
A,
Tardivel
A,
Tschopp
J.
Gout-associated uric acid crystals activate the NALP3 inflammasome
.
Nature
.
2006
;
440
(
7081
):
237
241
.
42.
Zhou
R,
Tardivel
A,
Thorens
B,
Choi
I,
Tschopp
J.
Thioredoxin interacting protein links oxidative stress to inflammasome activation
.
Nat Immunol
.
2010
;
11
(
2
):
136
140
.
43.
Nakahira
K,
Haspel
JA,
Rathinam
VA,
et al.
Autophagy proteins regulate innate immune responses by inhibiting the release of mitochondrial DNA mediated by the NALP3 inflammasome
.
Nat Immunol
.
2011
;
12
(
3
):
212
220
.
44.
Rathinam
VA,
Jiang
Z,
Waggoner
SN,
et al.
The AIM2 inflammasome is essential for host defense against cytosolic bacteria and DNA viruses
.
Nat Immunol
.
2010
;
11
(
5
):
395
402
.
45.
Krupa
A,
Kato
H,
Matthay
MA,
Kurdowska
AK.
Proinflammatory activity of anti-IL-8 autoantibody:IL-8 complexes in alveolar edema fluid from patients with acute lung injury
.
Am J Physiol Lung Cell Mol Physiol
.
2004
;
286
(
6
):
L1105
L1113
.
46.
Fudala
R,
Krupa
A,
Matthay
MA,
Allen
TC,
Kurdowska
AK.
Anti-IL-8 autoantibody: IL-8 immune complexes suppress spontaneous apoptosis of neutrophils
.
Am J Physiol Lung Cell Mol Physiol
.
2007
;
293
(
2
):
L364
L374
.
47.
Kurdowska
A,
Miller
EJ,
Noble
JM,
et al.
Anti-IL-8 autoantibodies in alveolar fluid from patients with the adult respiratory distress syndrome
.
J Immunol
.
1996
;
157
(
6
):
2699
2706
.
48.
Kurdowska
A,
Noble
JM,
Steinberg
KP,
Ruzinski
JT,
Hudson
LD,
Martin
TR.
Anti-interleukin 8 autoantibody: interleukin 8 complexes in the acute respiratory distress syndrome: relationship between the complexes and clinical disease activity
.
Am J Respir Crit Care Med
.
2001
;
163
(
2
):
463
468
.
49.
Kurdowska
A,
Noble
JM,
Grant
IS,
Robertson
CR,
Haslett
C,
Donnelly
SC.
Anti-interleukin-8 autoantibodies in patients at risk for acute respiratory distress syndrome
.
Crit Care Med
.
2002
;
30
(
10
):
2335
2337
.
50.
Terpstra
ML,
Aman
J,
Van Nieuw Amerongen
GP,
Groeneveld
AB.
Plasma biomarkers for acute respiratory distress syndrome: a systematic reviewand meta-analysis
.
Crit Care Med
.
2014
;
42
(
3
):
691
700
.
51.
Koh
H,
Tasaka
S,
Hasegawa
N,
et al.
Vascular endothelial growth factor in epithelial lining fluid of patients with acute respiratory distress syndrome
.
Respirology
.
2008
;
13
(
2
):
281
284
.
52.
Stern
JB,
Fierobe
L,
Paugam
C,
et al.
Keratinocyte growth factor and hepatocyte growth factor in bronchoalveolar lavage fluid in acute respiratory distress syndrome patients
.
Crit Care Med
.
2000
;
28
(
7
):
2326
2333
.
53.
Meduri
GU,
Annane
D,
Chrousos
GP,
Marik
PE,
Sinclair
SE.
Activation and regulation of systemic inflammation in ARDS: rationale for prolonged glucocorticoid therapy
.
Chest
.
2009
;
136
(
6
):
1631
1643
.
54.
Kress
JP.
Mortality is the only relevant outcome in ARDS: no
.
Intensive Care Med
.
2015
;
41
(
1
):
144
146
.
55.
Meduri
GU,
Kohler
G,
Headley
S,
Tolley
E,
Stentz
F,
Postlethwaite
A.
Inflammatory cytokines in the BAL of patients with ARDS: persistent elevation over time predicts poor outcome
.
Chest
.
1995
;
108
(
5
):
1303
1314
.
56.
Agrawal
A,
Zhuo
H,
Brady
S,
et al.
Pathogenetic and predictive value of biomarkers in patients with ALI and lower severity of illness: results from two clinical trials
.
Am J Physiol Lung Cell Mol Physiol
.
2012
;
303
(
8
):
L634
L639
.
57.
Calfee
CS,
Ware
LB,
Glidden
DV,
et al
National Heart, Blood, and Lung Institute Acute Respiratory Distress Syndrome Network. Use of risk reclassification with multiple biomarkers improves mortality prediction in acute lung injury
.
Crit Care Med
.
2011
;
39
(
4
):
711
717
.
58.
Ware
LB,
Koyama
T,
Billheimer
DD,
et al.
Prognostic and pathogenetic value of combining clinical and biochemical indices in patients with acute lung injury
.
Chest
.
2010
;
137
(
2
):
288
296
.

Competing Interests

The authors have no relevant financial interest in the products or companies described in this article.