Idiopathic Pulmonary Fibrosis
Fibrosis is a common feature in many chronic diseases and does not affect only the lungs—fibrosis can occur in every organ system. Such common conditions as atherosclerosis, chronic kidney disease, and fatty liver disease are fibrotic in nature. Because fibrosis interferes with normal tissue and organ function, it is an important contributor to organ failure (Kendall 2014; Vassiliadis 2013). It is estimated that fibrotic diseases account for 45% of deaths worldwide each year (Murtha 2017).
In IPF, the fibrotic process takes place in the interstitial tissues and spaces that surround and support the lungs' capillaries and air sacs (alveoli) (Murtha 2017). A similar pattern of interstitial lung scarring may be caused by radiation exposure, connective tissue diseases, certain medications, and inhaled irritants like asbestos, silica, and mold (Salvatore 2018); however, in IPF, the exact cause is not known (Plantier 2018).
The hallmark of fibrotic disease is overactive fibroblasts (ie, specialized cells found in connective tissue and interstitial spaces that form part of what is known as extracellular matrix). The extracellular matrix is made of collagen and other fibrous proteins, and provides structural support and cohesiveness to an organ's functioning cellular network. It also participates in intercellular communication. Fibroblasts play a critical role in wound healing and tissue repair, but in fibrotic diseases, an increase in their number and activity results in excessive production of extracellular matrix, leading to tissue stiffness and dysfunction (Murtha 2017; Kendall 2014; Frangogiannis 2016).