The chemical composition of trypanosomes. III. Antigenic constituents of Brucei trypanosomes

African trypanosomiasis research: 100 years of progress, but questions and problems still remain

Past and present progress in our understanding of African trypanosomiasis is briefly reviewed. Although tremendous scientific strides have been achieved, an epidemic of the disease is currently underway. Three areas of research which are believed necessary for the control of African trypanosomiasis are discussed. It is suggested that a better understanding of the host-parasite relationship is essential; more emphasis and a broader approach to drug development is required; and finally, further research into the socio-economic aspects of African trypanosomiasis is urgently needed before the human disease can again be controlled.

The adaptative mechanisms of Trypanosoma brucei for sterol homeostasis in its different life-cycle environments

Bloodstream forms of Trypanosoma brucei do not synthesize sterols de novo and therefore cannot survive in medium devoid of lipoproteins. Growth of parasites is essentially supported by receptor-mediated endocytosis of low-density lipoproteins (LDLs), which carry phospholipids and cholesteryl esters. These lipids are released from internalized LDL after apoprotein B-100 is degraded by acidic thiol-proteases in the endolysosomal apparatus and then metabolized, as in mammalian cells. The LDL receptor is recycled and its expression is regulated by the sterol stores. Documented pharmacological and immunological interferences with LDL receptor-mediated lipid supply to the bloodstream forms are summarized, and the potential for new approaches to fight against these parasites is evaluated. In contrast to bloodstream forms, cultured procyclic forms can acquire sterols from both exogenous (lipoprotein endocytosis) and endogenous (biosynthesis of ergosterol) sources. The rate-limiting steps of both endocytosis (surface LDL receptor expression) and biosynthesis (3-hydroxy-3-methylglutaryl coenzyme A reductase activity) are regulated by the cellular content of sterol. These two pathways thus complement each other to yield a balanced sterol supply, which demonstrates adaptative capacities to survive in totally different environments and fine regulatory mechanisms of sterol homeostasis.

The acquisition of lipids AfrAfrican trypanosomes

Bloodstream forms of African trypanosomes are dependent on their host for fatty acids, choline and other components of membrane lipids. The bulk of their choline requirement is met by their ability to take up lysophospholipids from the host tissue fluids. Trypanosoma brucei has ocyltransferose and phospholipase A(1) activities for the metabolism of exogenous lysophospholipids. The rate of uptake of lysophospholipids can be controlled by changes in the extrocellulor concentration of fatty ocyl-coenzyme A, and this control has potential for chemotherapy.

The fatty acids of Trypanosoma vivax

A study was carried out to determine the lipid composition of the blood-stream form of the African trypanosome. Trypanosoma vivax. Data from thin layer chromatography showed that the major polar lipids were lysophosphatidylcholine, sphingomyelin, phosphatidylcholine, phosphatidylethanolamine, phosphatidylserine and diphosphatidylglycerol. The major neutral lipids were sterol, monoacylglycerol, diacylglycerol, free fatty acid and triacyglycerol. 16:0, 18:0, 18:1 and 18:2 constituted the major fatty acids of both the polar and neutral lipid fractions. The work constituted the first detailed study on the fatty acid composition of this African trypanosome.

Glycoproteins released by Leishmania donovani: immunologic relationships with host and bacterial antigens and preliminary biochemical analysis

The antigenically active glycoproteins (AAGP) released by Leishmania donovani strain 3S promatigotes into growth media and by amastigotes of this strain into the tissue, e.g. blood, of infected hamsters was found to consist of 6 to 7 antigenically distinct components. The antigenic activity of these glycoproteins was resistant to freeze-thawing, protease treatment, and purification by column chromatography using Sephadex G-100. This activity, however, was destroyed by Na periodate and altered by boiling; AAGP adhered firmly to Amicon filter (UM2). The antigenically active substances absorbed UV at 230, 260, 280 nm and gave positive Folin phenol, phenol sulfuric acid, and orcinol reactions. By gel diffusion, the component glycoproteins were found to form lines with concanavalin A and to give reactions to identity and partial identity with human red cells and Mycobacterium butyricum. The possible involvement of the antigenically active glycoproteins in pathogenesis of kala azar is discussed.

Translation in a reticulocyte cell-free system of RNA isolated from blood and culture forms of Trypanosoma brucei

RNA with messenger activity has been extracted from both blood and culture (insect mid-gut) forms of Trypanosoma brucei and translated in a reticulocyte cell-free system. The products of this cell-free system have been compared, and many common polypeptides demonstrated. A major polypeptide of 58000--65000 molecular weight was made when both blood and culture form RNA was added to the cell-free system. Antiserum raised against purified variant antigen from a cloned variant (MIAG 099) was used to detect specific products of this system. A major polypeptide of approximately 58000-65000 molecular weight was precipitated when the homologous trypanosome (MIAG 099) blood form RNA was used in the cell-free system. No such polypeptide was precipitated when RNA from a heterologous strain culture or blood form was used in the system. Competition experiments, in which excess purified variant antigen was addded after incubation but before addition of specific antiserum, confirmed that the polypeptide of 58000--65000 molecular weight is the variant antigen.

Leishmaniasis in Brazil: X. Some observations of intradermal reactions to different trypanosomatid antigens of patients suffering from cutaneous and mucocutaneous leishmaniasis

In spite of the difficulty of antigen standardization, paired intradermal skin tests demonstrated qualitative differences between leishmanin and in vitro exo-antigen. Some of these differences may be due to the destruction of certain antigens by phenol, while others seem to reflect basic antigenic differences. Leishmania mexicana amazonensis in vitro exo-antigen produced immediate anaphylactic reponses in 74.4% of the patients with parasitologically proven cutaneous leishmaniasis. Although more individuals responded to leishmanin, 82.4% as compared to 73.9%, the leishmanial in vitro exo-antigen gave significantly larger delayed responses, Trypanosoma cruzi trypamosomin elicited delayed reactions, while trypanosomal in vitro exo-antigen only produced immediate anaphylactic reactions in persons with active cutaneous leishmaniasis.

Monosaccharide composition of the surface glycoprotein antigens of Trypanosoma brucei

Evidence has been adduced that the surface antigens ofTrypanosoma bruceisubgroup are a group of glycoproteins having D-galactose, D-mannose and D-glucosamine as monosaccharide components.

There was considerable variation in the number of antigen components, and their relative amounts, as revealed by isoelectric focusing on polyacrylamide gel. The relevance of these variations to the adaptation theory of antigenic variation in trypanosomes is discussed.