Pathophysiology and Genetics of Bronchiectasis Unrelated to Cystic Fibrosis

Bronchiectasis is characterized by deregulated inflammatory response and recurrent bacterial infection resulting in progressive lung damage and an irreversible dilatation of bronchi and bronchioles. Generally accepted model of the development of bronchiectasis is the “vicious cycle hypothesis” that proposes compromising of the mucociliary clearance by an initial event, which leads to the infection of the respiratory tract followed by further impairment of mucociliary function, bacterial proliferation, and more inflammation. Bronchiectasis is a very common symptom in patients with cystic fibrosis (CF), while bronchiectasis unrelated to CF is heterogeneous pathology of unknown cause with a large number of potential contributory factors and poorly understood pathogenesis. It is presumed that bronchiectasis unrelated to CF is a multifactorial condition predisposed by genetic factors. Different molecules have been implicated in the onset and development of idiopathic bronchiectasis, as well as modulation of the disease severity and response to therapy. Most of these molecules are involved in the processes that contribute to the homeostasis of the lung tissue, especially mucociliary clearance, protease–antiprotease balance, and immunomodulation. Evaluation of the studies performed towards investigation of the role these molecules play in bronchiectasis identifies genetic variants that may be of potential importance for clinical management of the disease, and also of interest for future research efforts. This review focuses on the molecules with major roles in lung homeostasis and their involvement in bronchiectasis unrelated to CF.