Granuloma formation and fibrosis in sarcoidosis

Sarcoidosis, a multisystem disorder, was previously defined by the presence of noncaseating epithelioid cell granuloma in affected organs following the exclusion of other known etiologic agents.¹ Because of new immunologic data accumulated in the past 10 years,^2,8 new criteria have been suggested for definition of sarcoidosis.⁴ Sarcoidosis should now be defined as a chronic, multisystem disorder characterized by an accumulation of inflammatory and immune effector cells,^5,6 noncaseating granuloma, and derangement of normal tissue architecture in affected organs. Bronchoalveolar lavage (BAL), done in conjunction with fiberoptic bronchoscopy, was widely used in the early 1970s-a technique to recover for analysis of protein and cell contents from human lungs.⁷ Numerous studies^8-47 about immunocompetent cells recovered by BAL from the lower respiratory tract of patients with Sarcoidosis have provided a better understanding of the immunologic events that take place at an important site of the disease-the respiratory tract. Although many organs can be affected by sarcoidosis, the lungs are most commonly involved (90%) and are the site of the disease that results in the highest morbidity and mortality,⁴⁸ mostly because of severe functional impairment that occurs in the interstitial fibrosis stage of advanced disease. Therefore, this review will focus on pulmonary Sarcoidosis because this is a major site of involvement.²⁰. Inflammation in the alveolar walls and air spaces, an initial host response to the disease process, causes an acute phase of mural and intraluminal alveolitis.⁴⁹ Following perhaps the consequences of prolonged or smoldering inflammation, adjacent portions of the interstitium and vasculature can be involved by granulomas. At this step, the disease-host interaction may proceed in either of two ways: spontaneous regression or progress to fibrosis and scarring that replaces the normal lung tissue with fibroblasts and a collagenous matrix produced by these cells.