Immunobiological studies on experimental visceral Leishmaniasis. V. The I-A(Bm12) mutation specifies resistance to infection

Susceptibility to visceral leishmaniasis in the domestic dog is associated with MHC class II polymorphism

Zoonotic visceral leishmaniasis (VL) is a disease of dogs, humans and other animals caused by the intracellular macrophage parasite Leishmania infantum. We examined the relationship between DLA class II alleles ( DRB1, DQA1, DQB1) and the course of infection in a cohort of Brazilian mongrel dogs exposed to natural L. infantum infection. DLA alleles were typed by sequence-based typing. DLA-DRB1 genotype was significantly associated with levels of anti- Leishmania IgG and parasite status assessed by PCR. Dogs with DLA-DRB1*01502 had higher levels of specific IgG and an increased risk of being parasite positive compared with dogs without this allele, controlling for other alleles and significant variables. No significant associations were seen for DLA-DQA1 or DLA-DQB1 alleles. These results suggest that the DLA-DRB1 locus plays a role in determining susceptibility to canine VL. As the domestic dog is the main reservoir for human infection, the identification of genetic factors influencing canine resistance or susceptibility to VL may provide insights into the immunology and potential control through vaccination of VL.

Early in vitro priming of distinct T(h) cell subsets determines polarized growth of visceralizing Leishmania in macrophages

An in vitro priming system of murine naive splenocytes was established to investigate early immune responses to Leishmania chagasi, the agent of visceral leishmaniasis in the New World. Priming of splenocytes from resistant C3H and CBA or susceptible BALB and B10 mice with L. chagasi resulted in blast transformation and in proliferating parasite-specific CD4(+) T cells secreting a differential complement of cytokines (IFN-gamma and low IL-10 levels for resistant T cells; IFN-gamma, IL-4 and high IL-10 levels for susceptible T cells). After priming, intracellular parasite load was much higher in susceptible than in resistant-type splenocyte cultures. On the other hand, infection of purified splenic macrophages from either resistant or susceptible mice with live L. chagasi promastigotes, resulted in comparable parasite loads. Moreover, when early CD4(+) T cell priming in splenocyte cultures was disrupted with anti-CD4 mAb, polarized parasite growth was abolished, becoming comparable in resistant and susceptible cultures. Neutralizing IL-4 activity during splenocyte priming did not affect the final parasite load in susceptible cultures. However, neutralizing IL-10 activity markedly decreased parasite load in susceptible, but not in resistant splenic macrophages. These results suggest that IL-10 plays an important role in L. chagasi infection in susceptible hosts. The results also indicate that innate control of growth of a visceralizing Leishmania in splenic macrophages results from the ability to activate different CD4(+) T cell subsets.

Use of an attenuated leishmanial parasite as an immunoprophylactic and immunotherapeutic agent against murine visceral leishmaniasis

The ability of the leishmanial parasite UR6 to act as an immunoprophylactic and immunotherapeutic agent against Leishmania donovani infection in BALB/c mice was investigated. Unlike the virulent L. donovani AG83 (MOHOM/IN/1983/AG83), UR6 given through intracardiac route failed to induce visceral infection, but when it was injected subcutaneously, UR6 induced a short-lived and localized self-healing skin lesion. Priming of peritoneal macrophages with UR6 in vitro induced superoxide (O(2)(-)) generation, whereas similar experiments with virulent AG83 inhibited O(2)(-) generation. It was observed that priming of mice with either live or sonicated UR6 in the absence of any adjuvant provided strong protection against subsequent virulent challenge. Further, UR6-primed infected mice not only displayed a strong antileishmanial delayed-type hypersensitivity (DTH) response but also showed an elevated level of the serum antileishmanial immunoglobulin G2a (IgG2a) isotype, whereas infected mice failed to mount any antileishmanial DTH response and showed an elevated level of IgG1. This indicates that UR6 priming and subsequent L. donovani infection allowed the expansion of Th1 cells. Our studies indicate that UR6 has potential to be used as an immunoprophylactic and immunotherapeutic agent against experimental visceral leishmaniasis.