Pleural fluid lysozyme in human disease

Lysozyme content was measured in the plasma and pleural fluid of 110 patients with pleural effusions of various causes. The concentration of pleural fluid lysozyme was significantly higher (P less than .001) in patients with tuberculous pleurisy than in those with primary pulmonary carcinoma, metastatic carcinoma of the lung, connective tissue disease, nonspecific pleurisy, or congestive heart failure. Tuberculous patients also had a significantly higher (P less than .001) pleural fluid-to-plasma lysozyme ratio than did the other patients. Plasma lysozyme activity did not differ significantly among the various patient groups. Lysozyme was identified immunohistochemically in epithelioid cell granulomas in tuberculosis, in activated macrophages in lymph nodes adjacent to tuberculous lesions, and in granulocytes in pleural empyema. No lysozyme was detected in neoplastic cells in pulmonary carcinoma. The results show that the determination of pleural fluid lysozyme is a simple, fast method for obtaining corroborative information in the differential diagnosis of tuberculous pleurisy.