MULTIPLICATION OF LEISHMANIA IN HUMAN MACROPHAGES INVITRO

To facilitate in vitro studies of the immunology of human leishmaniasis, a method of growing pathogenic Leishmania in human monocyte-derived macrophages was developed. After 6 days of incubation, adherent mononuclear cells were infected with L. donovani amastigotes obtained from infected hamster spleen cells or with L. tropica amastigotes obtained from infected BALB/c tissue mouse footpad. Of the macrophages, 48% were initially infected, with a mean of 3.0 amastigotes/infected macrophage. After 6 days of incubation, 59% of macrophages were infected and contained 8.8 amastigotes/infected macrophage, representing 2.9-fold multiplication. EM revealed the presence of dividing parasites within phagolysosomes. Leishmania may survive and multiply within human monocyte-derived macrophages despite fusion of secondary lysosomes with the parasitophorous vacuole.