Lungs defense

The standard unit normally used for measuring dust particles is the micron (pm one-thousandth of a millimeter). The smallest particle visible to the unaided eye is between 50 and 100 pm and the most dangerous sizes are between 0.2 and 5 pm. Particles larger than this are usually unable to penetrate the lung defenses and smaller ones settle out too slowly. Some dusts can be both toxic and fibrous (e.g. asbestos) and are therefore harmful even outside these parameters. It may therefore be assumed that dusts which are visible (i.e. between 50 and 100 pm), are quite safe. However, this is not the case, as dust clouds never consist solely of particles of one size. Analysis would show percentages of all sizes, and it is for this reason that special care is needed in measuring dust clouds and concentrations. 

Until recently, epithelial cells were considered to function solely as the ciliated barrier lining in the airways and as conduits for gas exchange at the air/blood interphase. As techniques have improved to isolate and culture these cells and measure their gene products, it has become clear that they have a key role in lung defense and repair. Epithelial cells secrete a number of anti-microbial compounds and immunoregulatory cytokines [52], and are also capable of ingesting and killing bacteria [53],... 

Arredouani, M., et al., The scavenger receptor MARCO is required for lung defense against pneumococcal pneumonia and inhaled particles, J. Exp. Med. 200, 2, 267, 2004. 

Nitrogen oxides Automobile emissions Fossil fuel power plants Pulmonary edema, impairs lung defenses Important component of photochemical smog and acid deposition... 

Ferric oxide has been shown to increase the metabolism of benzo[a]pyrene by hamster alveolar macrophages (Greife and Warshawsky 1993). Alveolar macrophages, the primary lung defense cell, have been shown to metabolize benzo[a]pyrene to a more biologically active from, and then release the metabolites. Concurrent exposure of hamster alveolar macrophages to benzo[a]pyrene-coated ferric oxide resulted in a significant increase in the amount of benzo[a]pyrene metabolites and superoxide anions, which have been shown to produce localized lipid peroxidation and edema in vivo... 

Yu H, Nasr SZ, Deretic V. Iimate lung defenses and compromised Pseudonwruis aeruginosa clearance in the malnourished mouse model of respiratory infections in cystic fibrosis. Infect Immun 2000 68 2142. 

But in reality, chemokines, the proteins that are the chemical messengers between cells and the immune system, attracted and retained the attention of biologists long before this time. Actually, the first chemokine, human monocyte-derived neutrophil chemotactic factor or interleukin 8 (IL-8), was identified in 1987 (2). Since then, scores of chemokines and their receptors have been identified, and we know they are prominent players in lung defense against infection. 

In normal conditions, secretion production is small and voluntary coughing is unproductive. However, when disease is present (such as in acute bronchitis), the molecular components change, production increases considerably, and sputum is formed from mucus, inflammatory cells, cell debris, and bacteria. Disruption of normal secretion or mucociliary clearance impairs pulmonary function and lung defense and increases risk of infection (14). However, it is not clear whether hypersecretion is only a marker of inflammation or a cause of pathological changes. There is even some evidence that stasis of mucus protects against inhaled material (15). 

Sibille Y, Reynolds HY. Macrophages and polymorphonuclear neutrophils in lung defense and injury. Am Rev RespirDis 1990 141 471-501. 

Newhouse M, Sanchis J, Bienenstock J. Lung defense mechanisms [part 1]. NEngl J Med 1976 295 990-996. 

Clarke RW, Hemenway DR, Frank R, Jakab GJ. Impairment of lung defenses following simultaneous exposure to respirable particulate matter and sulfur dioxide oeeurs at high, but not low, relative humidity. The Proceedings of The Society of Experimental Biology and Medicine, 1995 209 299. 

Koren HS, Becker S. Antimicrobial defense mechanisms. In Crystal RG, West JB, eds. The Lung Seientific Foundations. New York Raven Press, 1991 747-769. Sibille Y, Reynolds HY. Maerophages and polymorphonuclear neutrophils in lung defense and injury. Am Rev Respir Dis 1990 141 471-501. 

---