Promotion of leishmanial infections in non-permissive host macrophages by conditioned medium.

Leishmania enriettii grows well in guinea pig macrophages in culture but fails to do so in mouse macrophages. Dialyzed and concentrated conditioned medium from L. enriettii cultures promoted the infection in the mouse macrophages at 37 degrees C and at 32 degrees C. Similarly processed medium on which L. tropica had been cultured did not cause the same effect. Immune precipitation of the conditioned medium by anti-Leishmania serum cancelled out the effect. Infections of guinea pig macrophages by L. tropica were also enhanced by the homologous medium, but we were unable to quantitate the effect.