Developmental Life Cycle of Leishmania—Cultivation and Characterization of Cultured Extracellular Amastigotes1

The biochemistry and immunology of Leishmania promastigotes has been extensively studied; this is due primarily to the facility with which this stage, in contrast to the amastigotes stage, can be maintained in axenic culture. Several attempts to axenically culture lines of Leishmania amastigotes have been reported in the literature. This paper summarizes methods of adaptation (low pH, elevated temperature and culture medium) and characterization of several axenic lines of Leishmania amastigotes. Based on morphological, biological, immunological and biochemical evidence, these organisms appear to resemble amastigotes from infected macrophages or tissue. The axenically cultured amastigotes appear to be distinct from shocked (heat, serum deprivation, stressed) Leishmania promastigotes in the plethora of proteins synthesized, growth (multiplication) in culture, and developmental regulation observed. These data suggest that Leishmania organisms have a significant developmental response to certain signals (pH, temperature) mimicking their in vivo macrophage milieu. The response to other environmental parameters characteristic of the host-macrophage remain to be determined. These axenically cultured amastigotes should be of interest for further immunological, biochemical and developmental investigations of the disease-maintaining stage of this parasite.