Enzymes of carbohydrate metabolism in Leishmania donovani amastigotes

A method for the isolation of Leishmania donovani amastigotes from infected hamster spleen and liver tissues is described. Over 85% of the isolated amastigotes were viable as judged by acridine orange-ethidium bromide staining and in vitro transformation to the promastigote form. A comprehensive survey of the enzymes of carbohydrate metabolism in L. donovani amastigotes and promastigotes was conducted. Amastigotes and promastigotes possess all of the enzymes of the Embden-Meyerhof pathway, hexose monophosphate shunt, and tricarboxylic acid cycle. Cell-free extracts of both forms demonstrate an active glutamate dehydrogenase, thus linking activity which permits entry of pyruvate into the tricarboxylic acid cycle. Both forms demonstrate an active glutamate dehydrogenase, thus linking amino acid metabolism with carbohydrate metabolism. Pyruvate carboxylase, the enzyme responsible for replenishment of C4 acids by heterotrophic CO2 fixation into pyruvate, was also demonstrable in the tissue and insect forms. In general, activities of promastigote enzymes are higher than the amastigote enzymes. Differences between the vertebrate (amastigote) and invertebrate (promastigote) forms in their potential to utilize carbohydrates as substrates would appear to be quantitative rather than qualitative.

The characterization by isoenzyme electrophoresis of Leishmania isolated in the People's Republic of China

Seven isolates of Leishmania from mainland China were characterized on the basis of their isoenzyme profiles for 10 enzymes. Five isolates were from human visceral leishmaniasis patients, and four of these showed isoenzyme patterns similar to the marker strain of Leishmania infantum, while one was similar to L. donovani sensu lato. One isolate was from a presumed reservoir host of human visceral leishmaniasis, the racoon dog Nyctereutes procyanoides, and was isoenzymically indistinguishable from L. infantum. An isolate of L. gerbilli from the great gerbil Rhombomys opimus was readily distinguishable from Old World marker strains and other Chinese leishmanias. This is the first report of the biochemical characterization of Chinese isolates of Leishmania.

Clinical presentation of visceral leishmaniasis in Kenya: a prospective study of 64 patients

Clinical and laboratory findings of a series of 64 consecutive patients with visceral leishmaniasis are presented. The diagnosis was established by demonstration of parasites in splenic aspirates. Findings are discussed in comparison with those of former reports from Kenya and elsewhere.

Differential survival of Leishmania donovani amastigotes in human monocytes

Leishmania donovani is an important intracellular protozoal pathogen of man; it is found solely within macrophages in its amastigote stage in humans, and exists in its extracellular, flagellated promastigote stage in the sandfly, its arthropod vector. To determine if either stage of L. donovani was capable of surviving within monocytes--the oxidatively active precursors of tissue macrophages--interactions of the parasite with human monocytes were studied in vitro. Amastigotes and promastigotes were ingested to a comparable degree by monocytes; whereas 79% of promastigotes were killed within 48 hr, however, amastigotes survived and multiplied threefold over 5 days. Promastigotes, which have been shown to be sensitive to hydrogen peroxide-peroxidase-halide microbicidal mechanisms, elicited a phagocytic oxidative burst that was 49% of the response to serum-opsonized zymosan, as assessed by luminol-enhanced chemiluminescence. NBT was reduced to formazan in 71% of monocytes exposed to promastigotes. The death of promastigotes within monocytes could be attributed at least in part to oxidative microbicidal mechanisms because there was no significant decrease in the number of cell-associated parasites in monocytes from donors with chronic granulomatous disease of childhood. In contrast to promastigotes, amastigotes survived within monocytes, despite eliciting an oxidative response that was 27% of the response produced by serum-opsonized zymosan; this response was not significantly different from that produced by promastigotes. In a phagocyte-free system, amastigotes were found to be sevenfold more resistant than were promastigotes to the lethal effects of hydrogen peroxide. The survival of L. donovani in human monocytes is thus dependent on the parasite stage; promastigotes are ingested, they elicit an oxidative burst, and the majority are killed by oxidative microbicidal mechanisms, whereas amastigotes are ingested and survive to parasitize human monocytes successfully, despite eliciting a phagocytic oxidative burst.

Killing of intracellular Leishmania donovani by lymphokine-stimulated human mononuclear phagocytes. Evidence that interferon-gamma is the activating lymphokine

We have found that the crude lymphokines, which prime the human monocyte-derived macrophage to generate H2O2 and exert microbicidal activity against intracellular Leishmania donovani, are rich in interferon (IFN)-gamma (600-3,000 U/ml). To determine the role of this specific lymphocyte product in macrophage activation, lymphokines were pretreated with a monoclonal antibody that neutralizes human IFN-gamma. Antibody exposure completely abolished the capacity of both mitogen- and antigen-stimulated lymphokines to either enhance macrophage H2O2 release or induce leishmanicidal activity. In addition, partially purified and pure recombinant human IFN-gamma were as effective as crude lymphokines in activating macrophages, and 3 d of treatment with 300 U/ml resulted in a seven- to eightfold increase in H2O2 generation and the intracellular killing of both L. donovani promastigotes and amastigotes. The ability of crude lymphokines to induce monocytes and macrophages from a patient with chronic granulomatous disease to kill L. donovani promastigotes was similarly abrogated by anti-IFN-gamma antibody, and could also be achieved by IFN-gamma alone. These results suggest that IFN-gamma is the key macrophage-activating molecule present within human lymphokines, and indicate that IFN-gamma can enhance both the oxygen-dependent and -independent antiprotozoal mechanisms of human mononuclear phagocytes.

Immunoregulation of genetically controlled acquired responses to Leishmania donovani infection in mice: the effects of parasite dose, cyclophosphamide and sublethal irradiation

On a B10 (Lshs) genetic background, the development of acquired T cell mediated immunity to Leishmania donovani infection in mice is under H-2 linked genetic control. Following intravenous inoculation of 10(7) amastigotes three phenotypic patterns of recovery have been described: 'early cure' (H-2r,s), 'cure' (H-2b) and 'non-cure' (H-2d,q,f). In an attempt to determine the immunological basis for this H-2 linked genetic control the effects of varying parasite dose (5 x 10(3) to 5 x 10(7) amastigotes) and of pre-treatments with cyclophosphamide (50 or 200 mg/kg body weight CY) or sublethal irradiation (100 or 550 rad) on the course of infection, and on circulating anti-leishmanial IgG levels, were examined in strains representative of the three phenotypes: B10.D2/n (H-2d), C57BL/10ScSn (H-2b) and B10.RIII (H-2r). It was found that with low parasite doses (5 x 10(3) or 5 x 10(4)) 'non-cure' mice presented a 'cure' profile whilst raising the dose (5 x 10(7)) caused some perturbation of the normal self-curing response in 'cure' (but not 'early cure') mice. The highest dose did not, however, lead to progressive disease in the genetically non-cure strain. For the parasite dose experiments circulating anti-leishmanial IgG levels were higher in the early cure and cure strains than in the H-2d non-cure strain. The higher doses of CY and sublethal irradiation administered prior to infection had a clear prophylactic effect on the non-cure strain with some effect also observed in cure and early cure strains. This was thought to be due to deletion of the precursors of T suppressor (TS) cells suppressing cell-mediated immunity. Resolution of the liver parasite load in pre-treated mice took place despite minimal or undetectable levels of circulating anti-leishmanial IgG. Similarly, the earlier resolution of parasite load in pre-treated cure and early cure mice occurred even though the antibody response was severely reduced. This suggests that the high antibody responses observed in early cure and cure strains do not normally mediate cure and may simply reflect the independent effect of H-2 on T helper function or the humoral response.

Non-specific and specific stimulation of resistance against Leishmania donovani in C57BL/6 mice

Stimulation by intravenous injections of glucan, a beta 1,3 polyglucose, provided a significant degree of resistance in mice against Leishmania donovani. The response of C57BL/6 animals was dose-dependent. A single glucan injection before or after infection induced significant resistance but to a lesser degree than two or three injections. Immunization by injections of formalin-killed promastigotes with glucan via the subcutaneous or intravenous routes provided greater resistance than glucan or dead parasites alone against subsequent infection with viable parasites. Subcutaneous immunization with promastigotes from cultures passaged 10 times in vitro and those from cultures maintained for 25 passages elicited a similar degree of resistance against infection and induced positive skin test responsiveness against leishmanial antigen prior to infection.

Recognition of Leishmania donovani antigens by murine T lymphocyte lines and clones. Species cross-reactivity, functional correlates of cell-mediated immunity, and antigen characterization

Studies in man and experimental animals suggest that cell-mediated immunity is of primary importance in limiting the pathogenesis of cutaneous and visceral leishmaniasis. In an attempt to determine, more directly, the role of T lymphocytes and the nature of the antigens that activate them, we have propagated antigen-specific murine T lymphocyte lines and clones that proliferate in response to antigens present on the membrane of intact Leishmania donovani promastigotes. One such line cross-reacts with membrane antigens on seven other Leishmania species and, to a lesser extent, with antigens on African procyclic trypanosomes. T lymphocyte clones that also exhibited a broad range of species cross-reactivity were isolated. About 40% of these clones had highly restricted specificity, whereas 60% were more extensively cross-reactive. The parent line and some clones passively transferred footpad DTH when injected locally, and some secreted a lymphokine activity that elicited intracellular killing of amastigotes within infected macrophages. Although the proliferative response of most clones was H-2 restricted, two clones appeared to be reactive in the presence of allogeneic antigen presenting cells. The majority of the clones appeared to recognize carbohydrate containing antigens, and absorption with solid substrate-bound lectins indicated that these antigens contained both mannose and galactose ligands. The antigenic activity was also absorbed using either of two extensively cross-reactive anti-parasite monoclonal antibodies.

A comparison of three dosage regimens of sodium stibogluconate in the treatment of visceral leishmaniasis in Kenya

A prospective randomized trial of three dosage regimens of sodium stibogluconate (Pentostam; Wellcome Foundation, London) to treat visceral leishmaniasis was conducted. Previously untreated patients were randomized to receive 31 doses of sodium stibogluconate (10 mg Sb/kg of body weight per dose) administered once daily for 31 days (group A), every 12 hr for 15 days (group B), or every 8 hr for 10 days (group C). Of the 29 patients who completed treatment, seven of 10 in group B and all of the patients in groups A and C responded to treatment and remained well for one year. One patient in group B failed to respond to treatment, and two others in group B initially responded to treatment but relapsed six weeks after discharge. None of the treatment regimens was toxic. Parasites disappeared from splenic aspirates most quickly and hemoglobin levels rose most rapidly in patients receiving sodium stibogluconate every 8 hr. Treatment of visceral leishmaniasis in Kenya with sodium stibogluconate at a dose of 10 mg Sb/kg every 8 hr for 10 days appears to be a safe alternative to conventional treatment. Its efficacy should be confirmed in a larger number of patients.

Immunogenicity of soluble and particulate antigens from Leishmania donovani: effect of glucan as an adjuvant

The protective efficacy of glucan as an adjuvant with killed promastigotes of Leishmania donovani was compared with that of soluble or particulate fractions of the parasite. When these vaccine preparations were injected either intravenously or subcutaneously in CF-1 mice, glucan potentiated resistance against L. donovani infections as reflected by significant reductions in hepatic amastigote counts relative to infected control mice. The leishmanial antigens alone afforded no protection. Serum direct agglutination titers to leishmanial antigens were highest in all groups given the vaccine intravenously, whereas the delayed-type hypersensitivity response to the antigen was positive only in groups immunized subcutaneously with glucan as an adjuvant. Some index of protection and immune response against visceral infection with the parasite was seen in groups vaccinated with glucan and soluble antigens. However, the protection afforded by glucan and particulate antigens of L. donovani more closely paralleled the resistance of mice treated with glucan and unfractionated killed promastigotes. Further antigenic analysis of particulate fractions of L. donovani may optimize effective immunization when used with appropriate adjuvants, e.g., glucan.

Quantitation of amastigotes of Leishmania donovani in smears of splenic aspirates from patients with visceral leishmaniasis

During a 20-month period, more than 500 splenic aspirations were performed in 89 patients with suspected or proven visceral leishmaniasis. The two complications which occurred (intra-abdominal bleeding and penetration of the intestine in one patient each) both resolved with conservative management. Parasite density in splenic aspirate smears was graded on a logarithmic scale from 0 (no parasites in 1,000 microscopic fields) to 6+ (greater than 100 parasites per microscopic field). Among 46 newly diagnosed and 17 relapsed or drug-resistant patients with visceral leishmaniasis, the average initial parasite grade was 4.35 +/- 0.92 (mean +/- SD) and 4.15 +/- 1.37, respectively. The grading system was useful in measuring the speed of response to treatment, and in distinguishing slow responders from nonresponders. This was especially valuable for managing patients with drug-resistant visceral leishmaniasis. The system also provided a means of comparing the efficacy of different treatment regimens, and for calculating the optimum duration of treatment.

Surface antigens of Leishmania donovani promastigotes

Surface antigen profiles of Leishmania donovani promastigote isolates have been studied. Surface patterns of Brazilian and African isolates display remarkable similarities and are extremely simple, consisting of three major peptides of 65,000, 25,000, and 23,000 mol wt. Surface iodination and biosynthetic labeling coupled to immunoprecipitation techniques revealed that a single major determinant of 65,000 mol wt is recognized in all strains by sera from kala-azar patients from both Brazil and Africa. This major determinant is not brought down by sera from normal individuals and shows no significant cross-reactivity with sera from Chagas' disease, leprosy, or syphilis patients. Binding to concanavalin A suggests a glycoprotein nature for this antigen. Sera from patients with cutaneous leishmaniasis (L. braziliensis) also recognized the same 65,000-mol wt determinant, although to a lesser extent. The possibility that this major surface antigen is shared, with minor differences, not only by L. donovani strains but between Leishmania species in general is suggested.

Pyrazolopyrimidine metabolism in the pathogenic trypanosomatidae

Pyrazolopyrimidines are purine analogues. These compounds are metabolized by the pathogenic hemoflagellates and other members of the family Trypanosomatidae as though they were purines. This metabolic sequence does not exist in man or other mammals. In the hemoflagellates, the pyrazolopyrimidine base, of which allopurinol is the paradigm, undergoes ribosylphosphorylation to the ribonucleotide. This ribonucleotide may remain as such or be aminated to the amino analogue and further converted to the aminopyrazolopyrimidine ribonucleoside triphosphate. The latter is incorporated into RNA. This metabolic sequence has been demonstrated in the genera Leishmania and Trypanosoma.

Evidence for distinct 5'- and 3'-nucleotidase activities in the surface membrane fraction of Leishmania donovani promastigotes

A surface membrane fraction isolated from Leishmania donovani promastigotes contained distinct 5'- and 3'-nucleotidase activities. These were distinguished from each other, and from a previously described surface membrane nonspecific acid phosphomonoesterase, on the basis of several properties. The 5'- and 3'-nucleotidases had p' optima of 6.5 and 8.5, respectively. In contrast to the 3'-nucleotidase, the 5'-nucleotidase was inhibited by both ammonium molybdate and fluoride ions; the latter inducing a biphasic response. Neither divalent cations nor chelators affected the 5'-enzyme activity whereas the 3'-enzyme was inactivated by EDTA. This inactivation was fully reversed following removal of the chelator, either by resuspension of the membranes in EDTA free medium or by addition of certain divalent cations in excess; Co2+ being the most effective. The 5'-nucleotidase had activity with both ribo- and deoxyribonucleotide substrates, whereas the 3'-nucleotidase did not hydrolyse deoxyribonucleotides.

Interaction of Leishmania donovani promastigotes with human phagocytes

Leishmania donovani is an important intracellular protozoal pathogen of humans, which resides solely within mononuclear phagocytes. Phase-contrast microscopy and cinemicroscopy were used to examine the interaction of L. donovani promastigotes with human phagocytes to characterize and quantitate the sequence of events that results in leishmanial infection.

Clinical curio: Leishman-Donovan bodies in the duodenal mucosa of a child with kala-azar

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Comparison of microscopy and culture in the detection of Leishmania donovani from splenic aspirates

Three culture media were compared with Giemsa-stained smears for the detection of Leishmania in splenic aspirates from Kenyan patients with visceral leishmaniasis. Ninety-nine splenic aspirates obtained from 26 patients at various times before, during, and after treatment were cultured in Schneider's Drosophila medium and RPMI medium 1640 (each supplemented with 20% fetal bovine serum) and McConnell's modification of Senekje's medium overlayed with 0.9% saline. From 13 splenic aspirates obtained before treatment, amastigotes were identified microscopically in all and promastigotes were cultured in 12. During and after treatment, Schneider's medium was the most sensitive method for detecting parasites, followed by microscopic examination of stained smears which was more sensitive than either of the other two media tested. Results indicate that, for initial diagnosis, both culture and direct microscopy of aspirates should be employed.

Regulation of Leishmania populations within the host. V. Resistance to L.donovani in wild mice

Samples of wild Mus musculus from two populations in areas endemic for leishmaniasis and from seven populations in non-endemic areas were found to be uniformly resistant when tested for their early response to Leishmania donovani infection. Males from one endemic and one non-endemic population were crossed to females from two inbred strains of mice carrying the susceptible allele for the innate resistance gene, Lsh, on different genetic backgrounds. Bimodality of liver parasite counts and a close fit to Mendelian ratios obtained in F2 and backcross mice indicate that the uniform resistance observed in wild mice is most probably due to mono-morphism for the resistant allele at the Lsh locus. The relevance of these findings to the potential capacity of Mus musculus to act as a reservoir for visceral leishmaniasis for for other intracellular pathogens thought to be under the control of the same gene is discussed.