Role of Broncoalveolar Lavage in Diagnosis

The lung is continuously exposed to the external environment and mixtures of complex antigens through the air. It is estimated that the resting human adult inhales 12,000 liters of air per day, while even mild physical activity can double or triple this amount (1). Protective immunity against inhaled antigens is mediated by the lymphocytes that are localized to the surface of the respiratory tract. The compartments in the lung where lymphocytes are present are (i) the epithelium and lamina propria of the air-conducting regions, (ii) the bronchus-associated lymphoid tissue (found commonly in certain animals i.e. rabbit and rats) (iii) the pulmonary interstitium and vascular beds (iv) the bronchoalveolar space. In addition to anatomical barriers, such as airway angulation, mucociliary clearance, and coughing, both humoral and cellular defense mechanisms play an important role in maintaining the viability of the host. One of the first lines of defense against particulate matter is mucociliary clearance and phagocytic activity of alveolar macrophages. Antigens entering the pulmonary tract encounter antigen-presenting cells comprised of alveolar and interstitial macrophages and effector T lymphocytes.