Autoimmune pulmonary alveolar proteinosis in an adolescent girl with rapidly progressive dyspnea

Autoimmune pulmonary alveolar proteinosis (PAP) is a rare disease, especially in pediatrics, but important to consider, as it may avoid unnecessary and/or invasive investigations and delayed diagnosis. This case report highlights an adolescent girl with rapid onset dyspnea but an unremarkable physical exam and initial testing. However, due to a high index of suspicion, a chest computed tomography (CT) scan was done, revealing a "crazy paving" pattern, which then prompted expedited assessment. This finding, however, is not as specific as often discussed and has a broad differential diagnosis, which will be reviewed in detail as part of this case. Furthermore, this report demonstrates a diagnostic approach for PAP that avoids lung biopsy, previously considered to be required for diagnosis of PAP, but is increasingly becoming unnecessary with more advanced blood tests and understanding of their sensitivity and specificity. Additionally, management strategies for PAP will be briefly discussed.Copyright © 2022 Canadian Thoracic Society.

Pulmonary surfactant and COVID-19: A new synthesis

Chapter 1: COVID-19 pathogenesis poses paradoxes difficult to explain with traditional physiology. For instance, since type II pneumocytes are considered the primary cellular target of SARS-CoV-2;as these produce pulmonary surfactant (PS), the possibility that insufficient PS plays a role in COVID-19 pathogenesis has been raised. However, the opposite of predicted high alveolar surface tension is found in many early COVID-19 patients: paradoxically normal lung volumes and high compliance occur, with profound hypoxemia. That 'COVID anomaly' was quickly rationalised by invoking traditional vascular mechanisms-mainly because of surprisingly preserved alveolar surface in early hypoxemic cases. However, that quick rejection of alveolar damage only occurred because the actual mechanism of gas exchange has long been presumed to be non-problematic, due to diffusion through the alveolar surface. On the contrary, we provide physical chemical evidence that gas exchange occurs by an process of expansion and contraction of the three-dimensional structures of PS and its associated proteins. This view explains anomalous observations from the level of cryo-TEM to whole individuals. It encompasses results from premature infants to the deepest diving seals. Once understood, the COVID anomaly dissolves and is straightforwardly explained as covert viral damage to the 3D structure of PS, with direct treatment implications. As a natural experiment, the SARS-CoV-2 virus itself has helped us to simplify and clarify not only the nature of dyspnea and its relationship to pulmonary compliance, but also the fine detail of the PS including such features as water channels which had heretofore been entirely unexpected.Copyright ©

Possible Benefits of Reformulating Antiviral Drugs with Nanoemulsion System in the Treatment of Novel Coronavirus Infection

Background: An outbreak of SARS-CoV-2 (severe acute respiratory syndrome coronavirus 2) infection or COVID 19 has caused serious threats to all around the world. Until an effective and safe vaccine for novel coronavirus is developed by scientists, current drug therapy should be optimized for the control and treatment of COVID 19. Objective(s): In this manuscript, we present a perspective on possible benefits of reformulating antiviral drug dosage form with nanoemulsion system against novel coronavirus infection. Method(s): Literature review has been done on COVID 19, treatment strategies, novel drug delivery sys-tems and the role of pulmonary surfactant in lung protection. Result(s): Nanoemulsion system and its components have certain biophysical properties which could in-crease the efficacy of drug therapy. Antiviral drugs, delivered through a nanoemulsion system contain-ing P-gp inhibitor (surfactant and co-solvent), can minimize the cellular resistance to drugs and would potentiate the antiviral action of drugs. Pulmonary Surfactant (PS) assisted antiviral drug delivery by nanoemulsion system could be another effective approach for the treatment of COVID 19. The use of functional excipients like Pulmonary Surfactant (PS) and Surfactant Proteins (SPs) in the formulation of the antiviral drug-loaded nanoemulsion system can improve the treatment of coronavirus infection. Conclusion(s): In our opinion, for synergizing antiviral action, lipid and protein portion of PS and their commercial analogs should be explored by pharmaceutical scientists to use them as a functional excipi-ent in the formulation of antiviral drug-loaded nanoemulsion system.Copyright © 2021 Bentham Science Publishers.

Changes in surface activity of lung surfactant and bronchoalveolar cell profile upon COVID-19-related Acute Respiratory Distress Syndrome

A contribution of Lung Surfactant (LS) inactivation to COVID-19-related ARDS (cvARDS) has been argued, but not been clearly demonstrated to date. In the present study, we have characterised the extent of lung neutrophil infiltration along with the surface-active properties and protein composition of LS in bronchoalveolar lavages (BALs) collected from 12 cvARDS patients. A control group of 9 subjects without respiratory diseases was also enrolled. BAL cell sorting was performed by flow cytometry. The adsorption of LS at the air-liquid interface was assessed by Surfactant Adsorption Test (SAT), whereas the level of surfactant hydrophobic proteins was measured by Western Blot analysis. Results were normalised by phosphatidylcholine (PC) total amount. Significant increase in neutrophil [61.3(47.5-84.6)% vs 1.6(0.9-4.9)%, p<0.0001] and decrease in macrophage percentages [13.6(6.1-28.9)% vs 90.8(87.1-92-6)%, p<0.0001] of total BAL cells were detected in cvARDS patients. A lower overtime LS adsorption/accumulation at the air-liquid interface was also observed in those patients compared to the control group from 60min onward [14003(10232-19736) vs 24501(16386-28489) RFU, p=0.0471]. Moreover, cvARDS patients under the acute phase showed the lowest surfactant activity at the end of SAT (12191(11588-20159) RFU, p=0.048). An increase in both SP-B and SP-C/PC was also evident in cvARDS BALs. Here, we report for the first time on the reduction of LS surface-active properties during the acute period and even under the recovery phases of cvARDS. This may confirm how LS inactivation may be involved in both early and late consequences of severe cvARDS.

Synthetic Lung Surfactant Treatment for COVID-19 Pneumonia

COVID-19 has led to morbidity in millions of patients, ranging from mild flu-like symptoms to severe respiratory failure, necessitating oxygen supplementation and mechanical ventilation, and ultimately death. The SARS-CoV-2 virus reacts with angiotensin-converting enzyme 2 (ACE2) molecules that are especially found in alveolar epithelial type 2 cells in the lungs and thereby causes a loss in lung surfactant, a protein-lipid mixture that is crucial for both native immunity and reduction of surface ten-sion in the lung alveoli. Lung surfactant insufficiency results in atelectasis and loss of functional lung tissue amid an inflammatory storm and may be countered by treating COVID-19 pneumonia patients with exogenous lung surfactant, preferably by aerosol delivery of a novel dry powder synthetic lung sur-factant. More research on timing, dosing, and delivery of synthetic lung surfactant in patients with COVID-19 pneumonia is of crucial importance to implement this approach in clinical practice.Copyright © 2021 Bentham Science Publishers.

Administration of Exogenous Surfactant and Cytosolic Phospholipase A2alpha Inhibitors may Help COVID-19 Infected Patients with Chronic Diseases

Background: Coronavirus-19 (COVID-19) pandemic is a worldwide public health problem causing 347,070 deaths from December 25, 2019, till May 25, 2020. Phospholipids are structural components of mammalian cytoskeleton and cell membranes. Phosphatidylglycerol is an anionic lipid found in mammalian membranes in low amounts (1-2%) of the total phospholipids. Also, phosphatidylglycerol suppresses viral attachment to the plasma membrane and subsequent replication in lung cells. Phosphatidylglycerol depletion caused by over expression of cytosolic phos-pholipase A2alpha induces lipid accumulation in lung alveoli and promotes acute respiratory distress syndrome (ARDS). An exogenous-surfactant replacement has been successfully achieved in ARDS and improved oxygenation and lung mechanics. Inhibition of cytosolic phospholipase A2alpha impairs an early step of COVID-19 replication. Aim(s): The present study was carried out to explain the correlation between the administration of exogenous artificial surfactant as well as cytosolic phospholipase A2alpha inhibitors to improve oxygenation and lung mechanics and inhibit COVID-19 replication. Method(s): Database research was carried out on Medline, Embase, Cochrane Library, country-spe-cific journals, and following-up WHO reports published between December 25, 2019-May 25, 2020. Result(s): Till 25 May 2020, coronavirus cases were 5,307,298, with 347,070 deathsand 2,314,849 recovered cases. According to the WHO reports, most COVID-19 deaths seen are in people who suffered from other chronic diseases characterized by phospholipidosis and phosphatidylglycerol deficiency, including hypertension, liver, heart, and lung diseases and diabetes. Phospholipases A2 (PLA2) catalyze the cleavage of fatty acids esterified at the sn-2 position of glycerophospholipids leading to enhanced inflammation and lung damage. Also, cytosolic phospholipase A2alpha inhibitors may reduce the accumulation of viral proteins and RNA. In addition, administration of exogenous phospholipid surfactant may help COVID-19 infected patients with ARDS to remove inflammatory mediators. Conclusion(s): The present study showed a relation between phosphatidylglycerol deficiency in COVID-19 infected patients with ARDS and/or chronic diseases and their mortality. These findings also showed an important approach for the prevention and treatment of COVID-19 infections by using cytosolic phospholipase A2alpha inhibitors and exogenous administration of a specific phos-pholipid surfactant.Copyright © 2021 Bentham Science Publishers.

A UNIQUE CASE: ACUTE EOSINOPHILIC PNEUMONIA SECONDARY TO DAPTOMYCIN: A COVID-19 PNEUMONIA MIMIC

SESSION TITLE: Drug-Induced Lung Injury Pathology Case Posters SESSION TYPE: Case Report Posters PRESENTED ON: 10/19/2022 12:45 pm - 01:45 pm INTRODUCTION: Acute eosinophilic pneumonia (AEP) is an atypical cause of acute hypoxic respiratory failure in adults, however if not identified can prove to be fatal. It can all be a COVID19 mimic during the pandemic. AEP has several causes, such as inhalational drugs, infections and various pharmaceuticals. Often, patients will have an acute respiratory syndrome for less than one-month, pulmonary infiltrates on chest computed tomography (CT) or radiography (CXR), in addition to bronchoalveolar lavage (BAL) with more than 25% of eosinophils. CASE PRESENTATION: A 79 y/o man underwent an elective total knee replacement complicated by acute lower limb ischemia from an occluded bypass graft. He developed methicillin-resistant Staphylococcus aureus (MRSA) and Vancomycin-resistant Enterococcus (VRE) joint and soft tissue infection of the lower extremity. He was prescribed a 6-week course of Daptomycin. He presented about 3 weeks into treatment with shortness of breath. He was initially diagnosed with acute on chronic congestive heart failure (CHF) exacerbation and COVID negative. He was initially treated with diuretics. He developed acute renal failure requiring dialysis and acute hypoxic respiratory failure requiring intubation. CXR revealed bilateral lung infiltrates with BAL having 80% eosinophils, eosinophilia and urinalysis positive for eosinophils. Daptomycin was discontinued and he was started on systemic steroids for a two-week course. He was successfully extubated 5 days after diagnosis of AEP and was subsequently discharged to a rehabilitation facility on lifelong Doxycycline for MRSA prosthetic joint infection prophylaxis. DISCUSSION: AEP related to Daptomycin was first reported in 2007, in a patient that developed the condition after receiving treatment for endocarditis. Daptomycin caused an inflammatory reaction within the lungs, due to an accumulation of the drug within the pulmonary surfactant. Our case report patient met all components for AEP diagnosis, in addition to symptom onset being approximately 3 weeks into treatment. The ultimate treatment for AEP is to stop the reversible cause, if identifiable, along with glucocorticoids and symptomatic support. Prognosis for patients with AEP is excellent when diagnosis is prompt, and usually infiltrates are resolved within 1 month without long term adverse pulmonary effects. Our patient was discharged to an acute rehab facility without supplemental oxygen therapy and continues to improve from functional standpoint. This case a definite cause of AEP from Daptomycin presented as COVID19 pneumonia mimic. It highlights the importance of rapid diagnosis to prevent morbidity and mortality. CONCLUSIONS: The differential in a patient with acute hypoxic respiratory failure is numerous, especially during the COVID19 pandemic. During these challenging times, it is important to think of atypical causes, such as AEP to improve the patient's clinical status. Reference #1: Allen JN, Pacht ER, Gadek JE, Davis WB. Acute Eosinophilic Pneumonia as a Reversible Cause of Noninfectious Respiratory Failure. N Engl J Med. 1989;321:569-574 Reference #2: Hayes Jr. D, Anstead MI, Kuhn RJ. Eosinophilic pneumonia induced by daptomycin. J Infect. 2007;54(4):e211-213. Reference #3: Rachid M, Ahmad K, Saunders-Kurban M, Fatima A, Shah A, Nahhas A. Daptomycin-Induced Acute Eosinophilic Pneumonia: Late Onset and Quick Recovery. Case Reports in Pulmonology. 2017. DISCLOSURES: No relevant relationships by Moses Bachan No relevant relationships by Zinobia Khan No relevant relationships by Kaitlyn Mehern

DAPTOMYCIN-INDUCED EOSINOPHILIC PNEUMONITIS

SESSION TITLE: Drug-Induced Lung Injury Pathology Case Posters SESSION TYPE: Case Report Posters PRESENTED ON: 10/19/2022 12:45 pm - 01:45 pm INTRODUCTION: Daptomycin is an antibiotic that exerts its bactericidal effect by disrupting multiple aspects of bacterial cell membrane function. It has notable adverse effects including myopathy, rhabdomyolysis, eosinophilic pneumonitis, and anaphylactic hypersensitivity reactions. CASE PRESENTATION: A 46-year-old male with a history of type 2 diabetes presented with a 1-week history of dyspnea and productive cough. 2 weeks prior, he was started on vancomycin for MRSA osteomyelitis of the right foot, but was switched to daptomycin due to vancomycin induced nephrotoxicity. On presentation he was afebrile, tachycardic 100, hypertensive 183/109, tachypneic to 26, hypoxemic 84% on room air, which improved to 94% on nasal cannula. Chest exam noted coarse breath sounds in all fields and pitting edema of lower extremities were present. Labs showed leukocytosis of 15.2/L, Na of 132 mmol/L, and creatinine 3.20mg/dL (normal 1 month prior). COVID-19 testing was negative. Chest X-ray noted new bilateral asymmetric opacifications. Daptomycin was discontinued on day 1 of admission, he was started on IV diuretics and ceftaroline. Further study noted peripheral eosinophilia. Computed tomography of the chest showed bilateral centrally predominant ground-glass infiltrates with air bronchograms and subcarinal and paratracheal lymphadenopathy. On day 4, he underwent bronchoscopy with bronchoalveolar lavage. Cytology noted 4% eosinophil with 43% lymphocytes. Eventually, oxygen requirements and kidney function returned to baseline. He was discharged on ceftaroline for osteomyelitis DISCUSSION: Daptomycin-induced acute eosinophilic pneumonitis (AEP) often results in respiratory failure in the setting of exposure to doses of daptomycin >6mg/kg/day. It is characterized by the infiltration of pulmonary parenchyma with eosinophils and is often associated with peripheral eosinophilia. AEP has been associated with certain chemicals, non-steroidal anti-inflammatory agents, and antibiotics including daptomycin. Renal dysfunction is associated with an increased risk for developing AEP. The mechanism for daptomycin-induced lung injury is unknown but is believed to be related to daptomycin binding to pulmonary surfactant culminating in epithelial injury. Diagnostic criteria include recent daptomycin exposure, fever, dyspnea with hypoxemic respiratory failure, new infiltrates on chest radiography, BAL with > 25% eosinophils, and clinical improvement following daptomycin discontinuation. Our patient met four out of six criteria;we believe that BAL results were due to discontinuing daptomycin days before the procedure was performed. Sometimes stopping daptomycin is enough for recovery, however, steroids may be beneficial and were used in some of the cases reported in the literature CONCLUSIONS: Clinicians should consider AEP in a patient on Daptomycin presenting with respiratory failure, as timely discontinuation favors a good prognosis Reference #1: Uppal P, LaPlante KL, Gaitanis MM, Jankowich MD, Ward KE. Daptomycin-induced eosinophilic pneumonia - a systematic review. Antimicrob Resist Infect Control. 2016;5:55. Published 2016 Dec 12. doi:10.1186/s13756-016-0158-8 Reference #2: Kumar S, Acosta-Sanchez I, Rajagopalan N. Daptomycin-induced Acute Eosinophilic Pneumonia. Cureus. 2018;10(6):e2899. Published 2018 Jun 30. doi:10.7759/cureus.2899 Reference #3: Bartal C, Sagy I, Barski L. Drug-induced eosinophilic pneumonia: A review of 196 case reports. Medicine (Baltimore). 2018;97(4):e9688. doi:10.1097/MD.0000000000009688 DISCLOSURES: No relevant relationships by Chika Winifred Akabusi No relevant relationships by Shazia Choudry No relevant relationships by Hector Ojeda-Martinez No relevant relationships by Mario Torres

Plasma and Airway Levels of Surfactant Protein D Degradation Reflect Progression of ARDS in Ventilated Patients with SARS-CoV-2

Background: Patients with COVID-19 present severe respiratory symptoms progressing to acute respiratory distress syndrome (ARDS). Upon infection, SARS-CoV-2 destroys cells expressing the ACE2 receptor including alveolar type II cells (AT2). These cells are found in the alveolar-capillary barrier which normally secrete pulmonary surfactant, a complex of lipid and surfactant proteins (SPA, SP-B, SP-C, SP-D). Exogenous surfactant therapy (mainly composed of phospholipids, SP-B, and SP-C) has been successful in treating neonatal respiratory distress syndrome (nRDS) caused by surfactant deficiency in preterm babies.Plasma SP-D has been proposed as a marker of lung injury in COVID-19 but so far, no reports have evaluated sequential SP-D levels in both airway and plasma. As part of a clinical trial repurposing surfactant therapy to treat adult ventilated COVID-19 patients, we hypothesized that plasma SP-D levels may reflect decreased lung integrity and that SP-D degradation in plasma and airway samples from COVID-19 patients may reflect disease progression and severity. Methods: Enzyme-linked immunosorbent assay (ELISA) was used to quantify SP-D concentration in patient plasma and tracheal aspirate samples. Western Blotting was used to identify any protein degradation. Sequential daily plasma and airway samples were analysed. Results: SP-D concentration in serum was 10-20 times higher in patients ventilated for COVID-19 than in healthy volunteers. Additionally, the concentration of SP-D in plasma has shown to be 10-100-fold higher than in tracheal aspirates. Furthermore, degraded fragments of SP-D were detected at a higher ratio than intact SP-D in plasma of ventilated patients. This ratio decreased with administration of surfactant therapy (containing phospholipids and SP-B and SP-C but no SPA or SP-D). Conclusions: Increased serum SP-D and decreased tracheal aspirate SP-D from ventilated COVID-19 patients suggested leakage of pulmonary surfactant into the bloodstream caused by damage to the alveolar-capillary barrier in diseased lungs. The ratio of degraded vs. intact SP-D found in the plasma was compared before and after therapeutic surfactant administration. The results indicated that levels of SP-D in plasma and tracheal aspirates together with the ratio of degraded and intact SP-D in the plasma may be useful indicators of the severity of COVID-19 lung disease progression.

Pulmonary Surfactant Phospholipids as Novel Anti-Virals Against SARSCoV- 2 Infection

Background: A novel coronavirus (SARS-CoV-2) has led to the worldwide spread of pandemic proportions and currently no effective therapy is available. The minor pulmonary surfactant lipids, palmitoyl-oleoyl-phosphatidylglycerol (POPG), and phosphatidylinositol (PI), are potent regulators of inflammatory processes, and are effective as anti-viral agents for multiple respiratory viruses including Respiratory syncytial virus (RSV), Influenza A virus (IAV) and Rhinoviruses (RVs). Objective: The primary objectives of this study are to determine whether POPG or PI are potent against SARS-CoV-2 in vitro, using human airway epithelial cells, and examine the potency of PI against SARS-CoV-2 in vivo, in a hamster model. Methods: We examined efficacies of POPG or PI against SARS-CoV-2 (USA WA/2020) in human bronchial epithelial cells, and nasal epithelial cells from healthy control subjects differentiated by ALI cultures. We quantified SARS-CoV-2 replication by quantitative plaque assays and qRT-PCR. We determined the potency of PI against SARS-CoV- 2 in golden Syrian hamster as in vivo model for SARS-CoV-2 infection. Results: We examined the efficacies of POPG and PI using primary human tracheal and nasal epithelial cells, differentiated in ALI culture. Cells were treated with POPG (10mg/ml) and PI (4mg/ml) added to apical media alone for 16hrs. Subsequently, cells were infected with SARS-CoV-2 at m.o.i = 0.02, for 48hrs, harvested for RNA extraction and qRT-PCR. SARS-CoV-2 replicated in tracheal cells with a 106-fold increase in mRNA. POPG and PI reduced viral mRNA expression by 70% and 85%, respectively (subject numbers n=3). In nasal epithelia, SARS-CoV-2 mRNA expression increased 105 -fold compared to sham infected cultures. Both POPG and PI attenuated the increase in viral mRNA expression by 70% - 82% (subject numbers n=6). We determined the PI effect in an in vivo study in hamsters. Hamsters were challenged with 103 pfu of SARS-CoV-2, either with, or without PI (2mg/hamster) administered intranasally. Hamsters were harvested at Day 3, and lungs were processed for histopathology. Pharyngeal swabs were used to examine viral burden by plaque assays. PI reduced plaque numbers compared to viral infection alone groups at day1 (Virus alone: 2.4±2.7(X104pfu/ml), Virus+PI: 0.9±2.1(X106pfu/ml), p<0.05). PI reduced lung histopathology score at day 3 (Virus alone: 28.0±15.6, Virus+PI: 6.7±7.0, p<0.05). Conclusions: POPG and PI significantly reduced SARS-CoV2 replication in human differentiated airway epithelial cells. PI inhibited SARS-CoV-2 infection in vivo in hamsters. These findings suggest that inhalation of POPG, or PI might be effective as novel anti-viral compounds for treating and preventing SARSCoV- 2 infection.

Inhaled Placental Mesenchymal Stromal Cell Secretome from Two- and Three-Dimensional Cell Cultures Promotes Survival and Regeneration in Acute Lung Injury Model in Mice.

Acute lung injury (ALI) and acute respiratory distress syndrome (ARDS) is a common clinical problem, leading to significant morbidity and mortality, and no effective pharmacotherapy exists. The problem of ARDS causing mortality became more apparent during the COVID-19 pandemic. Biotherapeutic products containing multipotent mesenchymal stromal cell (MMSC) secretome may provide a new therapeutic paradigm for human healthcare due to their immunomodulating and regenerative abilities. The content and regenerative capacity of the secretome depends on cell origin and type of cultivation (two- or three-dimensional (2D/3D)). In this study, we investigated the proteomic profile of the secretome from 2D- and 3D-cultured placental MMSC and lung fibroblasts (LFBs) and the effect of inhalation of freeze-dried secretome on survival, lung inflammation, lung tissue regeneration, fibrin deposition in a lethal ALI model in mice. We found that three inhaled administrations of freeze-dried secretome from 2D- and 3D-cultured placental MMSC and LFB protected mice from death, restored the histological structure of damaged lungs, and decreased fibrin deposition. At the same time, 3D MMSC secretome exhibited a more pronounced trend in lung recovery than 2D MMSC and LFB-derived secretome in some measures. Taking together, these studies show that inhalation of cell secretome may also be considered as a potential therapy for the management of ARDS in patients suffering from severe pneumonia, including severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2), however, their effectiveness requires further investigation.

Fluid Films as Models for Understanding the Impact of Inhaled Particles in Lung Surfactant Layers

Pollution is currently a public health problem associated with different cardiovascular and respiratory diseases. These are commonly originated as a result of the pollutant transport to the alveolar cavity after their inhalation. Once pollutants enter the alveolar cavity, they are deposited on the lung surfactant (LS) film, altering their mechanical performance which increases the respiratory work and can induce a premature alveolar collapse. Furthermore, the interactions of pollutants with LS can induce the formation of an LS corona decorating the pollutant surface, favoring their penetration into the bloodstream and distribution along different organs. Therefore, it is necessary to understand the most fundamental aspects of the interaction of particulate pollutants with LS to mitigate their effects, and design therapeutic strategies. However, the use of animal models is often invasive, and requires a careful examination of different bioethics aspects. This makes it necessary to design in vitro models mimicking some physico-chemical aspects with relevance for LS performance, which can be done by exploiting the tools provided by the science and technology of interfaces to shed light on the most fundamental physico-chemical bases governing the interaction between LS and particulate matter. This review provides an updated perspective of the use of fluid films of LS models for shedding light on the potential impact of particulate matter in the performance of LS film. It should be noted that even though the used model systems cannot account for some physiological aspects, it is expected that the information contained in this review can contribute on the understanding of the potential toxicological effects of air pollution.

Chronic pharmacological antagonism of the GM-CSF receptor in mice does not replicate the pulmonary alveolar proteinosis phenotype but does alter lung surfactant turnover.

Granulocyte macrophage colony stimulating factor (GM-CSF) is a key participant in, and a clinical target for, the treatment of inflammatory diseases including rheumatoid arthritis (RA). Therapeutic inhibition of GM-CSF signalling using monoclonal antibodies to the α-subunit of the GM-CSF receptor (GMCSFRα) has shown clear benefit in patients with RA, giant cell arteritis (GCAs) and some efficacy in severe SARS-CoV-2 infection. However, GM-CSF autoantibodies are associated with the development of pulmonary alveolar proteinosis (PAP), a rare lung disease characterised by alveolar macrophage (AM) dysfunction and the accumulation of surfactant lipids. We assessed how the anti-GMCSFRα approach might impact surfactant turnover in the airway. Female C57BL/6J mice received a mouse-GMCSFRα blocking antibody (CAM-3003) twice per week for up to 24 weeks. A parallel, comparator cohort of the mouse PAP model, GM-CSF receptor ß subunit (GMCSFRß) knock-out (KO), was maintained up to 16 weeks. We assessed lung tissue histopathology alongside lung phosphatidylcholine (PC) metabolism using stable isotope lipidomics. GMCSFRß KO mice reproduced the histopathological and biochemical features of PAP, accumulating surfactant PC in both broncho-alveolar lavage fluid (BALF) and lavaged lung tissue. The incorporation pattern of methyl-D9-choline showed impaired catabolism and not enhanced synthesis. In contrast, chronic supra-pharmacological CAM-3003 exposure (100 mg/kg) over 24 weeks did not elicit a histopathological PAP phenotype despite some changes in lung PC catabolism. Lack of significant impairment of AM catabolic function supports clinical observations that therapeutic antibodies to this pathway have not been associated with PAP in clinical trials.