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The thick, dehydrated mucus that obstructs bronchioles sets off a vicious cycle of infection and inflammation. Interestingly, the immune response to lung infection in individuals with CF is not impaired and in fact may be too aggressive, leading to lung damage. In healthy lungs, introduction of bacteria results in a rapid influx of neutrophils, or white blood cells, and eradication of the bacteria. In CF patients, however, the production of certain compounds allows the bacteria to escape the normal immune response. In CF, neutrophils release lysosomes, bacteria-digesting enzymes resulting from phagocytosis, or cell death. A component of lysosomes called neutrophil elastase, or NE, is very damaging to the lung. The body has a defense mechanism, alpha 1–protease inhibitor, that inactivates NE. However, the ongoing presence of neutrophils in the airway overwhelms the body's normal NE inactivation. The presence of NE results in significant lung damage by several mechanisms, including destruction of lung tissue, increased airway gland secretion, reduced ciliary beat frequency and increased binding of Pseudomonas aeruginosa to the airway surface. The increased number of neutrophils also leads to increased oxygen radical production, and increased interleukin 8 (IL-8) and leukotriene B4 levels, which lead to further neutrophil recruitment.
| | Select from the menu above to compare the normal lung airway to the lung airway with CF and bacterial infection or with CF and inflammation. |
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