Trypanosoma cruzi amastigotes: development in vitro and infectivity in vivo of the forms isolated from spleen and liver.

Trypanosoma cruzi amastigotes were isolated from liver and spleen of previously infected mice and purified in discontinuous gradients of Metrizamide and Percoll. The amastigotes were well preserved as judged by electron microscopy. The amastigotes were readily interiorized by macrophages and multiplied actively within these cells in vitro. However, their capacity of differentiation was hampered as estimated by the absence of trypomastigotes until day 6 of cultivation. The purified amastigotes were infective for mice but the onset of parasitemia was somewhat delayed and less intense when compared to mice infected with trypomastigotes.