Effect of trypsin and 2-mercaptoethanol on the exposure of sugar residues on the surface of Leishmania donovani chagasi.

Using transmission electron microscopy, gold-labeled lectins, morphometry and enzyme-linked lectin assay, we could show that treatment of promastigotes of Leishmania donovani chagasi with trypsin did not interfere with the binding of lectins (concanavalin A, peanut agglutinin, wheat germ agglutinin and Ricinus communis agglutinin) to the parasite surface. These observations are in agreement with results we previously obtained using a biochemical approach. Treatment of fixed promastigotes with 2-mercaptoethanol induced a significant increase in the density of concanavalin A (Con A) receptors on the surface of L. d. chagasi in relation to the control. We suggest that this increase is due to the unfolding of one or more surface glycoproteins after cleavage of disulfide bonds between cystein residues in adjacent protein loops, exposing second-order Con A receptors that are otherwise hidden in the protein quaternary structure.

Interleukin 2 production in patients with Chagas' disease: correlation with anti-parasite antibody responses.

Peripheral blood mononuclear cells (PBMC) isolated from chronic chagasic patients and control individuals in Recife, Brazil were examined for the ability to produce IL-2 in response to concanavalin A (Con A) stimulation. Overall, there was little difference in the range of the response (IL-2 production) between the chagasic and control groups. Within the chagasic group, however, there was a high negative correlation between IL-2 production and the level of anti-parasite antibody. This correlation is thought to be a reflection of the fact that individuals with more recent or more vigorous infections exhibit higher anti-parasite antibody responses but also display a greater degree of immunosuppression, as reflected in depressed IL-2 production.

Trypanosoma cruzi: isolation of cloned strains and characterization of their infectivity.

Cloning of Trypanosoma cruzi strains Y, CL and Colombiana was achieved by plating on solid medium. Clones were obtained either from culture epimastigotes or from bloodstream trypomastigotes. In both cases the efficiency of plating was almost 100%. Clones from culture epimastigotes did not infect the albino mouse, while clones from bloodstream trypomastigotes remained infective even after several passages in a blood-agar/BHI biphasic medium, in which the amastigote-like forms prevail.

Environmental factors determining structural transition in herpetomonas samuelpessoai.

Transition from promastigote to paramastigote and opisthomastigote forms of Herpetomonas samuelpessoai in culture is dependent on environmental factors, among which paramount importance is attributed to the oxygen tension, which seems to play a decisive role in determining the choice between the aerobic and the anaerobic modes of respiration. A decrease of the oxygen tension and consequently of the pH, provokes the occurrence of structural transition, particularly in nonaerated cultures. In airgassed media, the changes in PO2 and pH occur at comparatively later stages of the culture and the cell volume does not change appreciably. A direct relationship has been found between the modal cell volume and the extent of structural transition as evaluated by the cell concentrations of the different forms in culture.

[Evolutive mechanisms in the epidemiology of the communicable diseases (author's transl)]. / Mecanismos evolutivos na epidemiologia das doenças transmissíveis.

Selective pressures playing on the interaction between an infectious agent and its host lead to a condition of maximal survival for both. Based on simple epidemiological relationships, we propose a model which permits the evaluation of the degree of adaptation of a host to the infectious agent.