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The role of these polymorphonuclear leukocytes and alveolar macrophages is to protect the terminal gas-exchange structures of the lungs from inhaled debris and infectious agents. Alveolar macrophages, derived from monocytes, also contain proteolytic enzymes. Leukocytes, specifically neutrophils (polymorphonuclear leukocytes), contain various proteolytic enzymes in their lysosomes. Serum levels of a1-PI of less than 11 mol/L or 80 mg/dL are considered deficient. The normal serum a1-PI concentration is 20 to 50 mol/L or 150 to 350 mg/dL. 6 This protein has been discovered to protect against other proteolytic enzymes and is now often referred to as a1-protease inhibitor (a1-PI). The specific protein that inhibited trypsin was identified later and was called a1-antitrypsin because of its inhibitory activity. Soon after, the suggestion was made that the serum’s inhibitory capacity conferred protection on tissues against proteolytic enzyme destruction. In 1905, Opie 5 discovered that white blood cells contained proteolytic enzymes. The roots of this theory extend to 1897, when Camus and Gley 4 recognized that serum had the capacity to inhibit the proteolytic enzyme trypsin.

The pathogenesis of emphysema is grounded in the protease and protease-inhibitor theory. Nonetheless, emphysema develops before 50 years of age in those born with a1–protease-inhibitor deficiency. 3 Emphysema usually occurs in people 50 or more years old, following decades of smoking. The relationship between cigarette smoking and the incidence of COPD is unusual in that almost 90% of patients with COPD have smoked, but only about 20% of smokers develop COPD.

Air quality, however, affects individuals who already have emphysema to the extent that air pollution can provoke an exacerbation.

Air pollution has been implicated as a cause, but no conclusive data support this notion. The prevailing cause of pulmonary emphysema is cigarette smoking. 2 The economic impact of emphysema in particular, and of COPD in general, will significantly contribute to the stress imposed on the health care system as average life expectancy increases. More than 17,800 deaths are attributable to emphysema in the United States each year.

1 The American Lung Association 2 ranks emphysema 15th among chronic conditions contributing to activity limitations, and 44% of patients with emphysema claim to have limitations in their daily living activities resulting from their disease. Among more than 14 million patients with COPD in the United States, 1.65 million have emphysema and 12.5 million are affected by chronic bronchitis. As a component of COPD, pulmonary emphysema causes health problems worldwide.