Exposure to Leishmania major modulates the proportion of CD4+ T cells without affecting cellular immune responses

The immune responses of individuals exposed to Leishmania major were evaluated and compared with those of non-exposed volunteers. Forty-one patients with active lesion(s), 43 healed individuals, 15 vaccinees 1 month or 1 year post vaccination, and 15 non-exposed volunteers were studied. Leishmanin skin test (LST) response, proliferative response of lymphocyte (PRL) to L. major antigen, IFN-gamma and IL-4 production, and percentage of L. major-specific CD4+, CD8+ and CD16+/CD56+ cells in peripheral blood mononuclear cells were assessed. Data showed positive LST (>5 mm) in 92% of patients, 98% of healed, and 80% or 43% of vaccinees 1 month and 1 year post vaccination, respectively. Positive PRL (SI>2.5) was displayed in 90%, 84%, 46% and 7% of patients, healed, vaccinated (post 1 year) and non-exposed donors, respectively. The mean +/-S.E. of IFN-gamma was 924 +/- 149, 1,278 +/- 185, 470 +/- 282 or 258 +/- 82 pg/ml in patients, healed cases and vaccinees after 1 month or 1 year, respectively. Positive IFN-gamma responders (>300 pg/ml) were shown in 72% of patients, 81% of healed cases, 31% or 39% of vaccinees and 0% of non-exposed donors. A reduced percentage of CD4+ T-cells and an increased percentage of NK cells were found in exposed individuals compared to non-exposed donors. The data indicated that exposure to L. major modulates the proportion of CD4+ T cells and increases NK cells percentage. However, the cellular immune responses including induction of LST, and IFN-gamma production are increased in exposed individuals.     

Calcium dependent thiol protease caldonopain and its specific endogenous inhibitor inLeishmania donovani

A calcium dependent proteolytic enzyme was detected in the lysed promastigotes ofLeishmania donovani, the causative agent of kala-azar. The protease was able to hydrolyse and added substrate, azocasein and showed high affinity for calcium. Rate of azocasein digestion was primarily slow but boosted up after eight hours. It was not inactivated when heated at 55° C for 15 min at pH 7.4. Sulfhydryl reagents significantly reduced the enzymic activity but trypsin-like protease inhibitors hardly had any effect. The enzyme was not sensitive to calmodulin from a heterologous source but registered low activity when treated with chlorpromazine. The caseinolytic activity was stimulated when leishmanial cells were preincubated with ionophore A23187 in presence of 1 mM Ca²⁺. The enzyme is named caldonopain due to its similarity with a general class of calcium dependent protease calpain present in different tissues and cells. Caldonopain was found to be localized in cytosol along with its specific endogenous inhibitor caldonostatin. The ratio of caldonopain-caldonostatin unit was higher in the infected macrophage compared to the parasitic protozoa and Balb/c macrophage alone. It may be postulated that the amount of both calcium and its protein inhibitor may have a direct impact on the caldonopain-induced biological process to regulate cellular action of this pathogen.Part of this work was presented at the International Symposium on Current Trends in Leishmania Research held in February, 1992 at Calcutta, India     

Synthesis and preliminary evaluation of new ursolic and oleanolic acids derivatives as antileishmanial agents

A series of new ursolic and oleanolic acids derivatives was synthesized via ursolic or oleanolic acids, previously extracted from South American Ilex species. These new compounds were tested for in vitro antiparasitic activity on Leishmania amazonensis and Leishmania infantum strains. Some of these compounds showed activity against the promastigote forms of L. amazonensis or L. infantum, with IC₅₀ ranging from 5 to 12 μM. As expected, most of the compounds showed a significant level of cytotoxicity against monocytes (IC₅₀ = 2-50 μM). From a structure-activity relationships point of view, these pharmacological results enlightened mainly the importance of an acetylation at position 3 of the oleanolic acid skeleton in the activity against the L. amazonensis strain, and of a bis-(3-aminopropyl)piperazine moiety on the carboxylic function of ursolic acid against the L. infantum strain.     

The structure of the transition state of the heterodimeric topoisomerase I of Leishmania donovani as a vanadate complex with nicked DNA

Type IB topoisomerases are essential enzymes that are responsible for relaxing superhelical tension in DNA by forming a transient covalent nick in one strand of the DNA duplex. Topoisomerase I is a target for anti-cancer drugs such as camptothecin, and these drugs also target the topoisomerases I in pathogenic trypanosomes including Leishmania species and Trypanosoma brucei. Most eukaryotic enzymes, including human topoisomerase I, are monomeric. However, for Leishmania donovani, the DNA-binding activity and the majority of residues involved in catalysis are located in a large subunit, designated TOP1L, whereas the catalytic tyrosine residue responsible for covalent attachment to DNA is located in a smaller subunit, called TOP1S. Here, we present the 2.27A crystal structure of an active truncated L.donovani TOP1L/TOP1S heterodimer bound to nicked double-stranded DNA captured as a vanadate complex. The vanadate forms covalent linkages between the catalytic tyrosine residue of the small subunit and the nicked ends of the scissile DNA strand, mimicking the previously unseen transition state of the topoisomerase I catalytic cycle. This structure fills a critical gap in the existing ensemble of topoisomerase I structures and provides crucial insights into the catalytic mechanism.     

Biochemical and immunological characterization of exometabolites from an Indian strain of Leishmania donovani promastigotes grown in a chemically defined medium

Summary Exometabolites (EXOM) of an Indian strain of Leishmania donovani promastigotes isolated from a chemically defined medium by ultrafiltration consisted of proteins, glycoproteins, lipid and lipophosphopolysaccharide (LPPS). LPPS of Mr 40-28 kDa in SDS-PAGE could be labelled metabolically with [³²P]-phosphate and recovered in the aqueous phase of hot-phenol-water extraction of EXOM (PE-Aq) along with a glycoprotein of Mr 150-130 kDa (GP_150-130) . These two molecules could be eluted from DE-52 column with 200 mM NaCI (D₂). The 300 mM NaCl (D₃) and 400 mM NaCl (D4) eluates from DE-52 column contained one unsaturated polar lipid component. The LPPS had Rf value of 0.65–0.75 in Thin Layer Chromatography (TLC) using saturated phenol water solvent system. EXOM revealed 15 bands in SDS-PAGE of which proteins of Mr 84, 66, 56, 50 and 29 kDa were prominent. When EXOM were fractionated through Con A — Sepharose column, the fraction eluted with -methyl-D-mannoside (Con A-E) had seven bands as revealed by SDS-PAGE of which 25, 16, 13 and 12 kDa glycoproteins were prominent.The antigens present in EXOM can be classified as slower anodic migrating and faster anodic migrating antigens as revealed by immunoelectrophoresis (IEP). The slower anodic migrating antigens, LPPS and GP_150-130 recovered in PE-Aq and D₂ did not cross-react with kala- azar patients' sera but cross-reacted with homologous anti-promastigote sera. Two faster anodic migrating antigens which could be recovered in organic phase of hot phenol extraction of EXOM (PE-O) and eluted in D₃ and D₄ and Con A-E, cross-reacted with kala-azar patients' sera. The antigens of both the classes were sensitive to periodic acid oxidation.     

Design,synthesis and evaluation of 3-(imidazol- 1-ylmethyl)indoles as antileishmanial agents. Part II

A new series of 1-benzyl-3-(imidazol-1-ylmethyl)indoles were synthesized according to a previous 3D-QSAR predictive model and assayed for their antiparasitic activity upon Leishmania mexicana promastigotes. The biological results obtained for these twelve molecules showed an IC₅₀ ranging from 2.3 to 32 μM and mainly illustrated the importance of the hydrophobic parameter the para-position of the benzyl group. In order to improve the activities of these compounds and to check the potential influence of the electronic parameter on this particular position, a Craig diagram was used to select original electro-donating and lipophilic substituents. Synthesis and biological evaluation of ten new compounds (IC₅₀ between 2.5 and 5.4 μM) confirmed that only the hydrophobic field is essential for a high level of activity.     

Binding pattern analysis and structural insight into the inhibition mechanism of Sterol 24-C methyltransferase by docking and molecular dynamics approach

Sterol 24-C methyltransferase (SMT) plays a major role during the production of steroids, especially in the biosynthesis of ergosterol, which is the major membrane sterol in leishmania parasite, and the etiological basis of leishmaniasis. Mechanism-based inactivators bind irreversibly to SMT and interfere with its activity to provide leads for the design of antileishmanial inhibitors. In this study, computational methods are used for studying enzyme–inhibitor interactions. fifty-seven mechanism-based inactivators are docked using 3 docking/scoring approaches (FRED, GoldScore, and ChemScore). A consensus is generated from the results of different scoring functions which are also validated with already reported experimental values. The most active compound thus obtained is subjected to molecular dynamics simulation of length 20 ns. Stability of simulation is analyzed through root-mean-square deviation, beta factor (B-factor), and radius of gyration (Rg). Hydrogen bonds and their involvement in the structural stability of the enzyme are evaluated through radial distribution function. Newly developed application of axial frequency distribution that determines three-particle correlation on frequency distributions before and after simulation has provided a clear evidence for the movement of the inhibitor into active pocket of the enzyme. Results yielded strong interaction between enzyme and the inhibitor throughout the simulation. Binding of the inhibitor with enzyme has stabilized the enzyme structure; thus, the inhibitor has the potential to become a lead compound.     

Ligation of Fc receptor of macrophages stimulates protein kinase C and antileishmanial activity

Fc receptors are known to express on the surface of mature monocytes macrophages and lymphocytes. In this study a ligand e.g. liposomal IgG (human IgG coupled to PE-liposome via carbodimide reaction) was developed to ligate the Fc receptor of macrophages. When liposomal IgG was incubated with macrophages at 37°C for 5 min, it induced the macrophage activation which suppress the parasite burden approximatley to an extent of 60%, 50% and 45%, when macrophages were infected with UR6, AG83 and GE1 strains of L-donovani respectively. Superior efficacy of liposomal IgG were achieved compared to the treatment with free IgG and free liposomes. The activity of protein kinase C (PKC) has been found to be higher in the Fc receptor targeted macrophage membrane fraction, suggesting its translocation from the cytosol. Staurosporine, a potent inhibitor of the enzyme protein kinase C (PKC) has been found to protect the parasite inside the macrophage indicating the role of PKC in the signaling process. The liposomal IgG treatment has been found to induce the generation of significant amount of superoxide and hydrogen peroxide which helped to suppress the parasite burden. Further when liposomal IgG were incubated with IFN- primed, LPS activated macrophages, a significant amount of NO release was also noticed, indicating its role in parasite killing. The above results suggest that Fc receptor mediated activation by liposomal IgG may be used as an alternative approach to kill parasites intracellularly.     

Leishmaniasis with oral mucosa involvement

doi: 10.1111/j.1741‐2358.2011.00512.x Leishmaniasis with oral mucosa involvement Introduction: The term leishmaniasis comprises a group of diseases caused by different protozoan species of the genus Leishmania. There are three main clinical forms of leishmaniasis: visceral, cutaneous and mucocutaneous. Exclusive involvement of the mucosa is very rare. Objectives: To present a case of mucocutaneous leishmaniasis in an elderly patient, discuss the clinical presentation, diagnostic process and treatment emphasizing the distinctions from other granulomatous lesions. Case report: A 71‐year‐old male presenting with a symptomatic lesion on the hard and soft palate, which had developed over a period of 6 months was evaluated. The oral exam revealed a lesion with multiple ulcerated nodules on the hard and soft palate extending to the oropharynx. The diagnostic hypothesis was chronic infectious disease (paracoccidioidomycose, tuberculosis and leishmaniasis) or squamous cell carcinoma. Histopathological, histochemical and immunohistochemical analysis were performed. A chest x‐ray revealed a normal pulmonary pattern. The Montenegro skin test was positive. The definitive diagnosis was leishmaniasis with exclusive oral manifestation and the patient was treated with liposomal amphotericin. Conclusions: Localized oral mucosa leishmaniasis is an uncommon event in an immunocompetent patient. Dentists play an important role in the diagnosis of oral leishmaniasis, which has systemic repercussions.     

Leishmania donovani Infection of a Susceptible Host Results in Apoptosis of Th1-Like Cells: Rescue of Anti-Leishmanial CMI by Providing Th1-Specific Bystander Costimulation

A protective immune response against Leishmania donovani infection is mediated by T-helper type 1 (Th1) cells. Th1 induced cell-mediated immunity (CMI), as assessed by anti-leishmanial DTH response, is lost in a susceptible host such as BALB/c mice. Although the impaired Th1 function eventuates in unhindered parasite growth and in manifestation of the susceptible phenotype, the mechanism of down-regulation of the Th1 function is yet to be elucidated. Here, we provide evidence that the parasite downregulates the expression of a Th1-specific costimulatory molecule, M150, on the surface of infected BALB/c mice-derived macrophages. Th cells are rendered unresponsive to anti-CD3 Ab-mediated stimulation after interaction with infected macrophages. The anergized T cells produce much less IL-2, IL-4 and IFN-γ compared to those T cells which were costimulated using normal macrophages. The defect in proliferation, anti-CD3 Ab induced unresponsiveness and IFN-γ but not IL-4 production can be restored by providing bystander costimulation through M150. These results not only unfold a novel immune evasion strategy used by the parasite but also clarify the mechanism of Th1 cell debilitation during the disease. Recovery of Th1 cytokine production by bystander costimulation through M150 may help in formulating a new strategy for the elimination of intracellular parasites.