Cystic Fibrosis is considered a multiorgan disease that affects the lungs, digestive tract, and reproductive organs (Huether, McCance, & Brashers, 2020). Clinical manifestations include high chloride content of sweat, meconium ileus, distal intestinal obstruction, exocrine pancreatic insufficiency, growth disturbance, male infertility, and chronic and recurrent pulmonary infections (Malhotra, Hayes, & Wozniak, 2019). This disease is characterized by airway obstruction, chronic bacterial infection, and excessive inflammatory response (Chmiel & Davis, 2003).
Cystic Fibrosis is caused by a mutation of the CFTR gene; this gene encodes the cystic fibrosis transmemberane conductance regulator (CFTCR). This mutation results in abnormal expression of cystic fibrosis transmembrane conductance regulator (CFTCR) protein (an activated chloride channel that exists on the surface of many types of epithelial cells). As a result of CFTR dysfunction, chloride and water are not transported appropriately across epithelial membranes and this results with thick and dry mucus secretions. Approximately 2,000 different mutations in the CFTR gene have been identified (Kiedrowski & Bomberger, 2018). These mutations are further subdivided into five classes based on how they lead to defective defective production of the CFTR protein (Kiedrowski & Bomberger, 2018). Chronic respiratory infections and ineffective inflammatory response leading to respiratory failure and primary causes in death of these patients (Kiedrowski & Bomberger, 2018).
Essentially, in the CF respiratory tract, there are numerous contributing factors that result from the dysfunctional CFTR protein combine to create a favorable environment for the promotion of chronic bacterial and viral infections.
It is suggested that CFTR dysfunction results in an inability to secrete chloride and bicarbonate ions into the airway lumen; unopposed sodium reabsorption results in net water uptake by the respiratory epithelium which liquid (further results in dehydration of airway surface (Malhotra, Hayes, & Wozniak, 2019). Dehydrated mucus affects mucociliary and cough clearance of mucus, thus providing a favorable environment for colonization and infection of opportunistic pathogens (Malhotra, Hayes, & Wozniak, 2019).
Another suggestion is that the impairment of CFTR is related to the altered pH of airway surface liquid (ASL). Studies suggest that CF ASL show reduced bacterial killing due to impaired function of cationic antimicrobial peptides (AMPs); AMPs are innate immune proteins within leukocyte and epithelial secretions, with broad antimicrobial activity against infectious pathogens and immunomodulatory functions (Malhotra, Hayes, & Wozniak, 2019). Antimicrobial killing of AMPs within the airway of those with CF, is said to be reduced in acidic pH conditions (Malhotra, Hayes, & Wozniak, 2019).
Furthermore, there is another suggestion that basal inflammation promotes bacterial infection. It is suggested that excess production of proinflammatory cytokines within the CF airway is related to early promotion and recruitment of inflammatory cells, such as neutrophils. Neutrophil proteases are able to degrade immune antimicrobials, thus contributing to a secondary bacterial infection (Malhotra, Hayes, & Wozniak, 2019).
Ultimately, the above-mentioned deficiencies in the CF respiratory tract prevent effective clearance of pathogens from the airway and create an environment favorable for infective pathogens.
References
Chmiel, J.F., & Davis, P.B. (2003). State of the Art: Why do lungs of patients with cystic fibrosis become
Infected and why can’t they clear the infection? Respiratory Research 4(1).
https://dx.doi.org/10.1186%2F1465-9921-4-8
Huether, S.E., McCance, K.L., & Brashers, V.L. (2020). Understanding Pathophysiology (7th ed.). Elsevier.
Kiedrowski, M.R., & Bomberger, J.M. (2018). Viral-Bacterial Co-Infections in the Cystic Fibrosis
Respiratory Tract. Frontiers in Immunology, 9. https://doi.org/10.3389/fimmu.2018.03067
Malhotra, S., Hayes Jr., D., & Wozniak, D.J. (2019). Cystic Fibrosis and Pseudomonas aeruginosa: the
Host-Microbe Interface. American Society For Microbiology 32(3).
https://doi.org/10.1128/CMR.00138-18.
