Nontypeable Haemophilus influenzae Clearance by Alveolar Macrophages Is Impaired by Exposure to Cigarette Smoke

Abstract

Nontypeable Haemophilus influenzae (NTHI) is an opportunistic gram-negative pathogen that causes respiratory infections and is associated with progression of respiratory diseases. Cigarette smoke is a main risk factor for development of respiratory infections and chronic respiratory diseases. Glucocorticoids, which are anti-inflammatory drugs, are still the most common therapy for these diseases. Alveolar macrophages are professional phagocytes that reside in the lung and are responsible for clearing infections by the action of their phagolysosomal machinery and promotion of local inflammation. In this study, we dissected the interaction between NTHI and alveolar macrophages and the effect of cigarette smoke on this interaction. We showed that alveolar macrophages clear NTHI infections by adhesion, phagocytosis, and phagolysosomal processing of the pathogen. Bacterial uptake requires host actin polymerization, the integrity of plasma membrane lipid rafts, and activation of the phosphatidylinositol 3-kinase (PI3K) signaling cascade. Parallel to bacterial clearance, macrophages secrete tumor necrosis factor alpha (TNF-␣) upon NTHI infection. In contrast, exposure to cigarette smoke extract (CSE) impaired alveolar macrophage phagocytosis, although NTHI-induced TNF-␣ secretion was not abrogated. Mechanistically, our data showed that CSE reduced PI3K signaling activation triggered by NTHI. Treatment of CSE-exposed cells with the glucocorticoid dexamethasone reduced the amount of TNF-␣ secreted upon NTHI infection but did not compensate for CSE-dependent phagocytic impairment. The deleterious effect of cigarette smoke was observed in macrophage cell lines and in human alveolar macrophages obtained from smokers and from patients with chronic obstructive pulmonary disease.

Impact of cigarette smoke exposure on host-bacterial pathogen interactions

“…Phosphoinositide 3-kinase (PI3K) signalling, including Akt phosphorylation, is required for NTHi phagocytosis by alveolar macrophages. Cell exposure to cigarette smoke diminishes phospho-Akt levels, which may account for the observed phagocytic deficiency; the same observations were made using immortalised macrophages and macrophages from bronchoalveolar lavage (BAL) from both smokers and COPD patients, compared with macrophages from neversmokers [41]. The levels of LPS-binding protein (LBP) and CD14 are higher in BAL from smokers and COPD patients than from never-smokers [86].…”

“…Thus, competition with H. influenzae in the commensal state turns pneumococci into more virulent populations, which may account for further development of invasive disease [85]. Although cigarette smoke does not seem to alter NTHi viability [41], host cell exposure to this irritant reduces bacterial invasion of respiratory epithelial cells (unpublished data) and alveolar macrophage phagocytic ability [39][40][41][42]. Normally, alveolar macrophages efficiently phagocytose and degrade NTHi by phagolysosomal fusion.…”

“…Cigarette smoke exposure also results in a suppression of neutrophil caspase-3-like activity, which ultimately impairs its phagocytic activity [38]. Importantly, cigarette smoke exposure causes an impairment of both alveolar macrophage and neutrophil phagocytic activity [39][40][41][42].…”

“…Central to this hypothesis is the notion that once pathogens have gained a foothold in the lower respiratory tract due to smoking-triggered impairment of mucociliary clearance, they persist by further blocking mucociliary clearance [28,75]. Cigarette smoke also upregulates mucus production, impairs epithelial elastic properties, downregulates the levels of IgA and affects the phagocytic activity of professional phagocytes [19,41]. Together, these alterations facilitate bacterial colonisation of the lower respiratory tract, which is associated with an exacerbation of the inflammatory response due to the recognition of PAMPs.…”

Cigarette Smoke Primes the Pulmonary Environment to IL-1α/CXCR-2–Dependent Nontypeable Haemophilus influenzae–Exacerbated Neutrophilia in Mice

“…It is possible that enhanced cellular inflammation is necessary to compensate for other aspects of host defense that are impaired by cigarette smoke. It has been established that cigarette smoke attenuates the phagocytic ability of macrophages, and this impairment has been specifically demonstrated in the context of NTHi (49). In addition to phagocytic activity, cigarette smoke also compromises the production of antimicrobial peptides and disrupts the integrity of the epithelial barrier.…”