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As the word "idiopathic" implies, the cause of IPF remains a mystery. Research indicates, however, that changes in the lungs' normal healing processes are involved. In interstitial lung diseases (ILDs), the lungs become chronically inflamed, promoting uncontrolled and exaggerated tissue repair (i.e., fibroproliferation and deposition of extracellular matrix) (7). Under the microscope, IPF lungs exhibit a unique pattern of alternating regions of normal tissue, interstitial inflammation, fibrosis, and "honeycombing" (cystic destruction). Although the exact mechanisms by which cellular injury occurs are unknown, activated alveolar macrophages and neutrophils appear to play a significant role in the pathogenesis of IPF (7).
The body's normal inflammatory response is characterized by four phases:
- Recognition—In this phase, the expression of adhesion molecules used for leukocyte trafficking is increased
- Recruitment—Neutrophils, lymphocytes, dendritic cells, and natural killer cells are trafficked in the presence of chemokines
- Removal—Th1 and Th2 cytokines are produced
- Resolution—Tissue integrity and function are restored via homeostatic mechanisms
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