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Bacterial pneumonia is a common clinical syndrome leading to significant morbidity and mortality worldwide. In the current study, we investigate a novel, multidirectional relationship between the pulmonary epithelial glycocalyx and antimicrobial peptides in the setting of methicillin-resistant Staphylococcus aureus (MRSA) pneumonia. Using an in vivo pneumonia model, we demonstrate that highly sulfated heparan sulfate (HS) oligosaccharides are shed into the airspaces in response to MRSA pneumonia. In vitro, these HS oligosaccharides do not directly alter MRSA growth or gene transcription. However, in the presence of an antimicrobial peptide (cathelicidin), increasing concentrations of HS inhibit the bactericidal activity of cathelicidin against MRSA as well as other nosocomial pneumonia pathogens ( Klebsiella pneumoniae and Pseudomonas aeruginosa ) in a dose-dependent manner. Surface plasmon resonance shows avid binding between HS and cathelicidin with a dissociation constant of 0.13 μM. These findings highlight a complex relationship in which shedding of airspace HS may hamper host defenses against nosocomial infection via neutralization of antimicrobial peptides. These findings may inform future investigation into novel therapeutic targets designed to restore local innate immune function in patients suffering from primary bacterial pneumonia. NEW & NOTEWORTHY Primary Staphylococcus aureus pneumonia causes pulmonary epithelial heparan sulfate (HS) shedding into the airspace. These highly sulfated HS fragments do not alter bacterial growth or transcription, but directly bind with host antimicrobial peptides and inhibit the bactericidal activity of these cationic polypeptides. These findings highlight a complex local interaction between the pulmonary epithelial glycocalyx and antimicrobial peptides in the setting of bacterial pneumonia.

Background: A comparison of pneumonias due to SARS-CoV-2 and influenza, in terms of clinical course and predictors of outcomes, might inform prognosis and resource management. We aimed to compare clinical course and outcome predictors in SARS-CoV-2 and influenza pneumonia using multi-state modelling and supervised machine learning on clinical data among hospitalised patients., Methods: This multicenter retrospective cohort study of patients hospitalised with SARS-CoV-2 (March-December 2020) or influenza (Jan 2015-March 2020) pneumonia had the composite of hospital mortality and hospice discharge as the primary outcome. Multi-state models compared differences in oxygenation/ventilatory utilisation between pneumonias longitudinally throughout hospitalisation. Differences in predictors of outcome were modelled using supervised machine learning classifiers., Findings: Among 2,529 hospitalisations with SARS-CoV-2 and 2,256 with influenza pneumonia, the primary outcome occurred in 21% and 9%, respectively. Multi-state models differentiated oxygen requirement progression between viruses, with SARS-CoV-2 manifesting rapidly-escalating early hypoxemia. Highly contributory classifier variables for the primary outcome differed substantially between viruses., Interpretation: SARS-CoV-2 and influenza pneumonia differ in presentation, hospital course, and outcome predictors. These pathogen-specific differential responses in viral pneumonias suggest distinct management approaches should be investigated., Funding: This project was supported by NIH/NCATS UL1 TR002345, NIH/NCATS KL2 TR002346 (PGL), the Doris Duke Charitable Foundation grant 2015215 (PGL), NIH/NHLBI R35 HL140026 (CSC), and a Big Ideas Award from the BJC HealthCare and Washington University School of Medicine Healthcare Innovation Lab and NIH/NIGMS R35 GM142992 (PS)., Competing Interests: Declaration of interests PGL- Present work: efforts were supported by, BJC HealthCare Healthcare Innovation Lab “Big Ideas” award, Doris Duke Charitable Foundation, and Fund to Retain Clinical Scientists, # 2015215. Outside scope of present work- CDC MMC- Outside scope of present work, grants to institution: DOD PRMRP W81XWH-21-1-0009, NIH/ NIDDK R01-DK126933A -01, NIH/ NIGMS R35-13362546, NIH/NIGMS, R01-GM123193. Patent pending ARCD. P0535US.P2. APM- Outside scope of present work: Pfizer personal stock ownership. TK- Outside scope of present work: Grants: NIA, AHRQ, NLM, NCATS, NIMH; Licenses: Springer, Elsevier; Consultant: Pfizer, Inc; Presentations and Events: Department of Defense. CCS- Outside scope of present work: Grants: NIH, Department of Defense, Roche-Genentech, Quantum Leap Healthcare Collaborative; Consultant: Vasomune, Gen1e Life Sciences, Cellenkos, Janssen. SLW. AD, KD, TMP, SVB, AB, PS, EHG, BNR, MK, and AM have no conflicts of interest to report., (Copyright © 2022 The Author(s). Published by Elsevier B.V. All rights reserved.)