Leishmania major: amastigote formation in cell-free media

The life cycle of Leishmania consists of two distinct developmental stages: the amastigote, which is the ovoid non-flagellated form found in the vertebrate host, and the promastigote, which is an elongated flagellated form found in the gut of an infected sandfly. Following its injection into the vertebrate host by the sandfly vector, the promastigote transforms into an amastigote after entering the host macrophage. The environmental cues inducing this transformation are not fully understood. Attempts to axenically develop and cultivate amastigotes from different Leishmania species have indicated that species and sometimes even strains of the same species vary in their requirements for this process (Pan et al., 1993). The majority of the available published data on transformation pertains to New World Leishmania and provides evidence that elevation in the incubation temperature and/or acidic pH can in some cases induce amastigote formation from promastigotes.