Metacyclogenesis of Leishmania spp: species-specific in vitro transformation, complement resistance, and cell surface carbohydrate and protein profiles.

Metacyclic (stationary) and logarithmic (log) forms of promastigotes of Leishmania donovani and Leishmania major were characterized in several ways. The highly active metacyclic forms were larger with more protein and less carbohydrate. The flagellum increased in length 2.4 times in L. major as compared to 1.8 times in L. donovani. Resistance to complement-mediated lysis by normal human serum of in vitro grown Leishmania promastigotes was related to the species, the growth phase in culture, and also the temperature. Metacyclic forms of both species had a much increased resistance to killing by normal serum at different temperatures. Differences in membrane-exposed carbohydrates were detected by fluorescein-conjugated lectins. Peanut agglutinin and Ulex agglutinin I differentiated log and stationary phase promastigotes of L. major. Higher amounts of acid phosphatase were demonstrated in the metacyclic phase. Differences in polypeptides were detected by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Two polypeptides of approximately 51 and 114 kDa were found exclusively in metacyclic promastigotes of both species, whereas 38- and 23-kDa polypeptides were lost or reduced during transformation from log to metacyclic phase promastigotes of L. donovani. In addition, a 75-kDa polypeptide was expressed only in metacyclic promastigotes of L. major.

A repetitive peptide of Leishmania can activate T helper type 2 cells and enhance disease progression.

Leishmaniasis provides a biologically relevant model to analyze the heterogeneity of CD4+ T cells and may lead to answering the major question of the mechanism for the preferential induction of T helper type 1 (Th1) and Th2 cells. Using synthetic peptides corresponding to the tandemly repeating regions of Leishmania proteins, we have identified an epitope that can preferentially induce the disease-exacerbating Th2 cells in susceptible BALB/c mice. Lymph node cells from BALB/c mice immunized subcutaneously with the octamer (p183) of the repeating 10-mer peptide EAEEAARLQA proliferated strongly against the peptide as well as the soluble antigen extract (SolAg) of Leishmania major. The proliferative T cells are CD4+, major histocompatibility complex class II restricted, and secrete interleukin 4 (IL-4) but little or no IL-2 and interferon gamma when stimulated with the peptide in vitro. T cells from BALB/c mice with progressive disease, but not from BALB/c mice cured of the infection, recognized this epitope. BALB/c mice injected subcutaneously with p183 developed significantly exacerbated disease when subsequently challenged with L. major. Furthermore, subcutaneous injection with p183 prevented the subsequent induction of resistance against L. major by intravenous immunization with soluble antigen. The T cell response to p183 is H-2d restricted. Immunization of the genetically resistant B10.D2 mice with p183 also produced strong T cell responses and exacerbated disease when challenged with L. major.

Elemental composition of polyphosphate-containing vacuoles and cytoplasm of Leishmania major.

Leishmania major promastigotes contain electron-dense vacuoles. The elemental composition of these vacuoles and of the cytoplasm was measured by electron probe X-ray microanalysis, using rapid cryopreservation techniques to prevent alterations in composition due to diffusion. The electron-dense vacuoles are rich in P, presumably present as polyphosphate (poly P). Mg is present at about 9 times its cytoplasmic level. There is sufficient Mg to largely neutralize most of the negative charge of the Poly P. The electron-dense vacuoles also contain appreciable amounts of Ca and Zn, which are not detectable in the cytoplasm, as well as Na, K, and Cl, the latter two at concentrations below that of the cytoplasm. These results suggest that the vacuolar membranes have at least one cation transport system. Incubation of the promastigotes for 1 h in the absence of phosphate in the presence or absence of glucose did not cause significant changes in the vacuolar contents of P, Mg, or Zn, but changes in K and Cl content were observed in both the electron-dense vacuoles and in the cytoplasm.

The leishmanial lipophosphoglycan: a multifunctional molecule.

A striking characteristic of leishmanial parasites is their ability to avoid destruction in hostile environments throughout their life cycle. To survive, the parasites must have evolved specialized molecules. One such molecule that has received considerable attention is an unusual glycoconjugate called lipophosphoglycan. The macromolecule is the major cell surface glycoconjugate of all Leishmania promastigotes. This minireview summarizes current information on the structure and possible functions of this intriguing molecule.

Characterization of integral membrane proteins of Leishmania major by Triton X-114 fractionation and analysis of vaccination effects in mice.

The total integral membrane proteins of promastigotes of Leishmania major were extracted by using the Triton X-114 phase separation technique and were characterized by immunoprecipitation, Western blotting (immunoblotting), and lectin chromatography. Of the 40 or more proteins which partitioned into the detergent phase, only about 10 proteins could be surface radioiodinated on live promastigotes, suggesting their surface orientation. The abundance of the gp58-63 antigen varied markedly between two strains of L. major. Sera from patients with visceral leishmaniasis caused by Leishmania donovani chagasi recognized the gp58-63 complex and an additional Mr-42,000 polypeptide shared between L. major and L. donovani chagasi. A subpopulation of six surface proteins, including the abundant gp58-63 antigen and a group of proteins of Mr 81,000 to 105,000, were glycoproteins recognized by antiserum to wheat germ agglutinin- or concanavalin A-binding proteins. The membrane proteins of the LRC-L119 isolate of L. major could successfully vaccinate genetically susceptible mice, thus opening the way for a molecularly defined subunit vaccine composed of glycolipid and membrane protein antigens.