Dysfunctional CFTR Alters the Bactericidal Activity of Human Macrophages against Pseudomonas aeruginosa

Abstract

Chronic inflammation of the lung, as a consequence of persistent bacterial infections by several opportunistic pathogens represents the main cause of mortality and morbidity in cystic fibrosis (CF) patients. Mechanisms leading to increased susceptibility to bacterial infections in CF are not completely known, although the involvement of cystic fibrosis transmembrane conductance regulator (CFTR) in microbicidal functions of macrophages is emerging. Tissue macrophages differentiate in situ from infiltrating monocytes, additionally, mature macrophages from different tissues, although having a number of common activities, exhibit variation in some molecular and cellular functions. In order to highlight possible intrinsic macrophage defects due to CFTR dysfunction, we have focused our attention on in vitro differentiated macrophages from human peripheral blood monocytes. Here we report on the contribution of CFTR in the bactericidal activity against Pseudomonas aeruginosa of monocyte derived human macrophages. At first, by real time PCR, immunofluorescence and patch clamp recordings we demonstrated that CFTR is expressed and is mainly localized to surface plasma membranes of human monocyte derived macrophages (MDM) where it acts as a cAMP-dependent chloride channel. Next, we evaluated the bactericidal activity of P. aeruginosa infected macrophages from healthy donors and CF patients by antibiotic protection assays. Our results demonstrate that control and CF macrophages do not differ in the phagocytic activity when infected with P. aeruginosa. Rather, although a reduction of intracellular live bacteria was detected in both non-CF and CF cells, the percentage of surviving bacteria was significantly higher in CF cells. These findings further support the role of CFTR in the fundamental functions of innate immune cells including eradication of bacterial infections by macrophages.

Anti-Pseudomonas aeruginosaIgY antibodies promote bacterial opsonization and augment the phagocytic activity of polymorphonuclear neutrophils

“…40 Various aggravating mechanisms have been proposed, for instance, reduced phagocytic priming of PMNs recruited to the lungs, 41 defective production of intraphagosomal bactericidal hypochlorous acid (HOCl) 42 or the presence of high levels of human neutrophil peptides in sputum, which counteracts the phagocytic activity of PMNs in a negative feedback manner. 43 Nevertheless, the observed reduced phagocytic activity of CF PMNs is controversial, and while the ROS production by murine CFTR deficient alveolar macrophages is attenuated, 44 the intrinsic production of ROS by PMNs derived from CF patients is normal. 45 Interestingly, the imperative IgG receptor Fcg RIII (CD16) is downregulated in PMNs isolated from CF sputum, 44 suggesting that non-Fc receptor-mediated phagocytosis by CF PMNs may be important.…”

“…43 Nevertheless, the observed reduced phagocytic activity of CF PMNs is controversial, and while the ROS production by murine CFTR deficient alveolar macrophages is attenuated, 44 the intrinsic production of ROS by PMNs derived from CF patients is normal. 45 Interestingly, the imperative IgG receptor Fcg RIII (CD16) is downregulated in PMNs isolated from CF sputum, 44 suggesting that non-Fc receptor-mediated phagocytosis by CF PMNs may be important. Thus, the effect of specific IgY antibodies on the phagocytic competence of PMNs from healthy donors may be even more prominent in CF conditions because of the possible diminished bactericidal activity of PMNs from CF patients.…”

Bacterial host interactions in cystic fibrosis

“…Another aspect of host defense that is compromised in CF is macrophage clearance of pathogens. Recent evidence suggests that dysfunctional CFTR in macrophages impairs bacteriocidal activity against P. aeruginosa [19], but the specific role of CFTR in macrophage killing remains undefined and controversial. Many humoral components of immunity are also ineffective in CF.…”

Macrophage Polarization and Function in Cystic Fibrosis

“…Depending on the post translational processing, three isoforms of CFTR proteins have been shown in earlier studies (176) human macrophages (160). Conversely, the presence of isoform B was detected in monocytes from patients with CF (176,180).…”

“…Truncated forms of the protein appear to be loosely localized on the membrane. Macrophages from CF patients homozygous for F508 mutation showed cytoplasmic localization of CFTR protein indicating trafficking defect due to class II CFTR mutation (160).…”