Cigarette Smoke Exposure Promotes Virulence of Pseudomonas aeruginosa and Induces Resistance to Neutrophil Killing.

It is widely known that cigarette smoke damages host defenses and increases susceptibility to bacterial infections. Pseudomonas aeruginosa, a Gram-negative bacterium that commonly colonizes the airways of smokers and patients with chronic lung disease, can cause pneumonia and sepsis and can trigger exacerbations of lung diseases. Pseudomonas aeruginosa colonizing airways is consistently exposed to inhaled cigarette smoke. Here, we investigated whether cigarette smoke alters the ability of this clinically significant microbe to bypass host defenses and cause invasive disease. We found that cigarette smoke extract (CSE) exposure enhances resistance to human neutrophil killing, but this increase in pathogenicity was not due to resistance to neutrophil extracellular traps. Instead, Pseudomonas aeruginosa exposed to CSE (CSE-PSA) had increased resistance to oxidative stress, which correlated with increased expression of tpx, a gene essential for defense against oxidative stress. In addition, exposure to CSE induced enhanced biofilm formation and resistance to the antibiotic levofloxacin. Finally, CSE-PSA had increased virulence in a model of pneumonia, with 0% of mice infected with CSE-PSA alive at day 6, while 28% of controls survived. Altogether, these data show that cigarette smoke alters the phenotype of P. aeruginosa, increasing virulence and making it less susceptible to killing by neutrophils and more capable of causing invasive disease. These findings provide further explanation of the refractory nature of respiratory illnesses in smokers and highlight cigarette smoking as a potential driver of virulence in this important airway pathogen.

Analysis of the effects of cigarette smoke on staphylococcal virulence phenotypes.

Cigarette smoking is the leading preventable cause of death, disease, and disability worldwide. It is well established that cigarette smoke provokes inflammatory activation and impairs antimicrobial functions of human immune cells. Here we explore whether cigarette smoke likewise affects the virulence properties of an important human pathogen, Staphylococcus aureus, and in particular methicillin-resistant S. aureus (MRSA), one of the leading causes of invasive bacterial infections. MRSA colonizes the nasopharynx and is thus exposed to inhalants, including cigarette smoke. MRSA exposed to cigarette smoke extract (CSE-MRSA) was more resistant to macrophage killing (4-fold higher survival; P < 0.0001). CSE-MRSA demonstrated reduced susceptibility to cell lysis (1.78-fold; P = 0.032) and antimicrobial peptide (AMP) (LL-37) killing (MIC, 8 µM versus 4 µM). CSE modified the surface charge of MRSA in a dose-dependent fashion, impairing the binding of particles with charge similar to that of AMPs by 90% (P < 0.0001). These changes persisted for 24 h postexposure, suggesting heritable modifications. CSE exposure increased hydrophobicity by 55% (P < 0.0001), which complemented findings of increased MRSA adherence and invasion of epithelial cells. CSE induced upregulation of mprF, consistent with increased MRSA AMP resistance. S. aureus without mprF had no change in surface charge upon exposure to CSE. In vivo, CSE-MRSA pneumonia induced higher mouse mortality (40% versus 10%) and increased bacterial burden at 8 and 20 h postinfection compared to control MRSA-infected mice (P < 0.01). We conclude that cigarette smoke-induced immune resistance phenotypes in MRSA may be an additional factor contributing to susceptibility to infectious disease in cigarette smokers.

Myeloid cell HIF-1α regulates asthma airway resistance and eosinophil function.

Hypoxia-inducible factor (HIF)-1α is a master regulator of inflammatory activities of myeloid cells, including neutrophils and macrophages. These studies examine the role of myeloid cell HIF-1α in regulating asthma induction and pathogenesis, and for the first time, evaluate the roles of HIF-1α and HIF-2α in the chemotactic properties of eosinophils, the myeloid cells most associated with asthma. Wild-type (WT) and myeloid cell-specific HIF-1α knockout (KO) C57BL/6 mice were studied in an ovalbumin (OVA) model of asthma. Administration of the pharmacological HIF-1α antagonist YC-1 was used to corroborate findings from the genetic model. WT, HIF-1α, and HIF-2α KO eosinophils underwent in vitro chemotaxis assays. We found that deletion of HIF-1α in myeloid cells and systemic treatment with YC-1 during asthma induction decreased airway hyperresponsiveness (AHR). Deletion of HIF-1α in myeloid cells in OVA-induced asthma also reduced eosinophil infiltration, goblet cell hyperplasia, and levels of cytokines IL-4, IL-5, and IL-13 in the lung. HIF-1α inhibition with YC-1 during asthma induction decreased eosinophilia in bronchoalveolar lavage, lung parenchyma, and blood, as well as decreased total lung inflammation, IL-5, and serum OVA-specific IgE levels. Deletion of HIF-1α in eosinophils decreased their chemotaxis, while deletion of the isoform HIF-2α led to increased chemotaxis. This work demonstrates that HIF-1α in myeloid cells plays a role in asthma pathogenesis, particularly in AHR development. Additionally, treatment with HIF-1α inhibitors during asthma induction decreases AHR and eosinophilia. Finally, we show that HIF-1α and HIF-2α regulate eosinophil migration in opposing ways.