Setting New Immunobiological Parameters in the Hamster Model of Visceral Leishmaniasis for In Vivo Testing of Antileishmanial Compounds

Abstract

To establish suitable immunobiological parameters for in vivo testing of new antileishmanial compounds in the golden hamster model of visceral leishmaniasis, two groups of 8 animals were infected each with 10(5) or 10(7) stationary promastigotes by the intracardiac route and the clinical and immunoparasitological features were monitored up to day 155 after infection. All animals became infected at both doses, although significant differences were observed between parasite burdens in liver and spleen. The mean number of parasites in animals infected with 10(7) promastigotes increased by 9.5 times in liver and by 43.1 times in spleen compared with those infected with 10(5) promastigotes. In animals given the higher dose, the outcome of the disease occurred between days 75 and 90 after infection, whereas no signs of disease were apparent in those given the lower infecting dose. Positive antibody (IgG) responses were detected earlier (week 5-7 after infection) in animals infected with the higher dose than in those infected with the lower dose (week 8-10 after infection), but these responses did not correlate with individual parasitological loads in liver and spleen. An inverse correlation was observed between infecting doses and in vitro spleen lymphocyte proliferation against mitogens (ConA). The proportion of CD4(+) and CD19(+) spleen cell increased in animals given the higher infection, whereas it decreased in those given the lower infection compared to naive controls.

Therapeutic effect of ursolic acid in experimental visceral leishmaniasis

“…However, this effect should not be understood as immunosuppression, since mononuclear cells of this group proliferated under stimulation with concanavalin A (data not shown). Previous studies also indicated that spleen cells from golden hamsters treated with free or encapsulated amphotericin B did not proliferate under specific stimuli (Dea-Ayuela et al., 2004, Dea-Ayuela et al., 2007), but such findings should not be considered as immunossuppresion, since concanavalin A-stimulated cells proliferated.…”

Parasite Burden in Hamsters Infected with Two Different Strains of Leishmania (Leishmania) infantum: “Leishman Donovan Units” versus Real-Time PCR

“…Given the number of amastigotes per 1000 nuclei cells but without consideration of the organ weight, the spleen appeared to be more parasitized than the liver. Higher splenic parasitism has been shown by many other researchers in studies that used hamsters experimentally infected by L. infantum and/or L. donovani with different infective forms (amastigote and promastigote) and routes of inoculation [6], [7], [19], [21], [22], [47]. The discrepancy in results presented by others authors can be explained because of the use of limiting dilution for assessing parasitism in spleen and liver without including organ weight in the calculation of parasite load.…”

“…Our results are consistent with Requena et al [7] who associated the strong humoral response in hamsters experimentally infected with L. infantum to the presence of clinical signs and elevated parasite tissue density. Other studies have shown a relationship between parasite load and high antibody titers in hamsters experimentally infected with different forms and species of Leishmania [6], [21], [22], [29]. Thus, similarly to human and canine LV, the evaluation of anti- Leishmania antibody is an important tool in monitoring the establishment of infection in the hamster model.…”

“…The quantification of parasitism in hamsters experimentally infected with L. infantum or L. donovani is generally determined by classical methods, such as limiting dilution and/or by Leishman Donovan units (LDU) according to Stauber [19]; however, these methods exhibit low sensitivity [20], [21], [22]. The development of a technique that allows quantifying the amastigotes in different parasitized tissues is extremely important to evaluate the impact of parasitism in experimentally infected hamsters.…”

Modeling of leishmaniasis infection dynamics: novel application to the design of effective therapies

“…A significant reference for the latter is the work of Courret et al [16] where lesion development, cellular response, expression of cytokines, as well as parasite load in the spleen of BALB/c mice infected with L. amazonensis is described. In this vein there are also the works of Arrais-Silva et al [17] on the hypoxia-inducible factor-1 from L. amazonensis infection ; of Lira et al [18] on BALB/c mice symptoms, parasite load and immune response in C57BL/6 mice infected with L. major ; and the work of Requena et al [19] and of Dea-Ayuela et al [20] that explores the clinical symptoms, parasite loads and antibody levels in susceptible, oligosymptomatic and resistant hamsters. The study of Requena et al [19] compared these parameters together with lymphocyte population and proliferation, in two groups infected with different amounts of parasites and a control group.…”