Human monocyte activation by supernatants from continuous cultures of Plasmodium falciparum.

When mononuclear cells derived from the blood of unsensitized adult Caucasians are incubated for 22 hours with supernatants from cultures of Plasmodium falciparum, there is a substantial stimulation of the phagocytic capacity of the adherent monocytes for anti-D sensitized red cells. This stimulatory effect is dependent on (i) a heat-stable factor in such supernatants, (ii) the presence of T lymphocytes in the mononuclear cell preparations and (iii) the occurrence of DNA synthesis in the mononuclear cell cultures. It is proposed that the malaria culture supernatant contains a mitogen which acts on non-allergized T lymphocytes and that the stimulation of such lymphocytes probably causes the release of a lymphokine which enhances the phagocytic activity of cells of the mononuclear phagocyte system.