Macrophages in resistance to rickettsial infections: characterization of lymphokines that induce rickettsiacidal activity in macrophages.

Lymphokine-rich culture supernatants of antigen- or mitogen-stimulated spleen cells were fractionated by Sephadex G-200 column chromatography; fractions were assayed for capacity to induce tumoricidal and rickettsiacidal activities in mouse macrophages. Lymphokine activity that activated macrophages for tumor cytotoxicity eluted as a single peak in the 45,000 m.w. region. In contrast, activity for intracellular killing of rickettsiae eluted in 3 distinct regions: 115 to 125,000, 35 to 45,000, and less than 10,000 daltons. This elution pattern was observed with both antigen and mitogen-induced lymphokines. Activity of each of the 3 lymphokine species for induction of rickettsiacidal activity was destroyed by heating at 56 degrees C for 1 hr. Tumor cytotoxicity and rickettsiacidal activity, both effector functions of activated macrophages, were dissociated on the basis of lymphokines regulating these activities.