The tuberculin reaction in the pleural cavity and its suppression by antilymphocyte serum.

Tuberculin (PPD) injected into the pleural cavity of sensitized guinea-pigs results in the development of a large protein-rich effusion over a period of 24 hours. In the early stages the effusion contains large numbers of polymorphonuclear leucocytes, but later mononuclear cells (lymphocytes and monocytes) predominate. At 24 hours a small percentage of the lymphocytes have the character of lymphoid blast cells, while some of the monocytes contain phagocytosed polymorphonuclear cells or nuclear debris. A similar phenomenon can be elicited in mice sensitized with complete Freund's adjuvant. However, in these animals the volume of the effusion is small and difficult to measure accurately. The effusion in the guinea-pig is completely suppressed by antilymphocyte serum (ALS). This effect is relatively long lasting (compared with its transient action on a nonspecific inflammatory lesion due to turpentine) and recovery parallels the return of the tuberculin reaction in the skin—providing further confirmation that the effusion is due to delayed hypersensitivity. The tuberculin PPD reaction in the pleural cavity provides a useful model of delayed hypersensitivity in which exudate and viable inflammatory cells can be collected for study during the development of the lesion.