The Fine Structure of Leishmania donovani and the Role of the Kinetoplast in the Leishmania‐Leptomonad Transformation*

Abstract

SYNOPSIS. An electron microscope study of Leishmania donovani revealed major differences between the intracellular leishmanial and the extracellular leptomonad stages. Parasites were also removed from infected hamster spleen, inoculated into cultures, and examined at intervals during incubation in order to follow changes during the transformation from one stage to the other. Prominent changes are evident primarily in the kinetoplast and the nucleoli after several hours of cultivation when the parasite is in an intermediate stage of transition. The kinetoplast, a composite organelk containing DNA and cristae mitochondriales, is a regular, sausage‐like structure in the leishmanial stage, but becomes irregular and enlarges extensively after a few hours in vitro, developing branches that are mitochondrial in nature and which, very likely, become new mitochondria. In the nucleus, significant nucleolar changes occur. The two homogeneous nucleoli characteristic of the leishmanial stage merge during transformation into one which is larger, less compact, and composed of small centrally located granules about 100 Å in diameter and larger particles over 200 Å in diameter at the periphery. These transformations of the kinetoplast and nucleolus are undoubtedly expressions of adaptive changes in the metabolic pattern of an intracellular parasite transferred to a markedly different extracellular environment of much lower temperature. It was also found that the leishmanial stage of the parasite has two unit membranes which extend over the flagellum and the flagellar pocket; the intermediate stage and the leptomonad have only a single membrane. Furthermore, some leishmanias in spleen cells were found to be covered by a capsule‐like structure formed by the deposition of fine granular material between the two unit membranes. Since two to four organisms were occasionally found within such capsules, it is possible that encapsulation is a preparatory step for reproduction.

Some Aspects of Intracellular Parasitism

“…By construct validity we mean that the predictor or criterion should be relevant to what we intend to measure. Specifically, it should represent what we want to measure, all we want to measure, and nothing but that which we want to measure (2). By reliability we mean that a measure provides a stable estimate from one measuring occasion to another.…”

Tubulin biosynthesis in the developmental cycle of a parasitic protozoan, Leishmania mexicana: changes during differentiation of motile and nonmotile stages.

“…At various periods up to 7 days, parasites were isolated from 107 infected cells by vortex mixing in phosphate-buffered saline (PJNaCl) containing 2 mM EDTA followed by centrifugation in 45%/ 90% step Percoll (Pharmacia) gradient in PJNaCl, as described (3). For amastigote-to-promastigote differentiation, leishmanias were isolated from macrophage cultures infected with promastigotes for at least 10 (25), and stored at -700C.…”

“…Amastigote-topromastigote transformation has been found to require amino acids and glucose (8). It is accompanied by an increase in polyamine levels (9), in mitochondrial volume (10,11), and in respiratory rate (12). Cyclic AMP (13), ionophores (14), actinomycin D, puromycin (8), cycloheximide, antileishmanial drugs (15), and lymphocyte factors (16,17) have been reported to inhibit or to perturb this transformation.…”

Generation of adenosine tri-phosphate in Leishmania donovani amastigote forms

“…This might be the reason for the survival of amastigote cells within the phagolysosomes where apparent hypoxic condition persists (James et al 1998, McConville et al 2007. Amastigotes have poorly developed mitochondria (Rudzinska et al 1964) and the spleen which is parasitized by L. donovani amastigotes is also poorly oxygenated (Wennberg and Weiss 1969). Table II showed the formation of ATP in presence of various electron donors and acceptors in terms of elimination of inorganic phosphate exclusively in presence of ADP.…”