Activity in Vitro of Lymphocytes and Macrophages in Delayed Hypersensitivity

The in vitro activities and interactions of macrophages and lymphocytes from tuberculin-sensitive and normal guinea pigs, in the presence or absence of antigen (PPD), were examined with the aid of phase-contrast time-lapse cinematography. Macrophages from peritoneal exudate had active amoeboid motion and numerous rapidly extending pseudopodia. Macrophages from normal or sensitized animals, in the presence of antigen and sensitized lymphocytes, and to a lesser extent sensitized thymocytes, formed considerably less active and less numerous pseudopodia, became spherical and were more sluggish in their movements. The motion of lymphocytes and thymocytes, normal or sensitized, was not affected by specific antigen. Non-sensitized macrophages aggregated and tended to become associated with lymphocytes in the presence of antigen and sensitized lymphocytes. These in vitro observations provided direct evidence of immunologically induced cellular interactions in delayed hypersensitivity systems.