Influência da carga parasitária e do sítio de inoculação na imunopatogênese da leishmaniose cutânea causada por Leishmania braziliensis em hamster

Abstract

Leishmania braziliensis is the main causative agent of cutaneous leishmaniasis in Brazil and despite its importance for public health, there is a lack of an experimental model that can be used for testing new therapies and vaccines. The aim of this study was to investigate the influence of parasite burden and the inoculation site in the immunopathogenesis of cutaneous leishmaniasis caused by Leishmania braziliensis in hamsters using ear dermis infection model. Groups of animals (n = 48) were infected intradermally in the ear (n = 24) or paw (n = 24) with 105 promastigotes of L. braziliensis. Afterwards, other groups of animals (n=32) were infected intradermally in the ear with 105 (n=16) or 106 (n=16) promastigotes. The lesions were measured every 5 days for 60 days. The animals were euthanized at 30, 45 and 60 d.p.i., and had their infected ears and paws, as well as lymph nodes (retromaxilar or popliteal), livers and spleens collected for evaluation of parasite burden and expression of inflammatory mediators, and analysis of histopathological changes. The lesions arose at 20 d.p.i. both paw and ear. The ear lesions ulcerated and were bigger (p< 0.0001) in contrast to paw lesions that presented themselves as small nodules without ulcers. It was observed significant parasitic burden in the ear after 30, 40 and 60 d.p.i. at the lesion and in the lymph node, with parasite burden being always bigger at the lesion. Regardless of the route of inoculation, neither liver and spleen were enlarged nor had lumps or parasites. In the retromaxillary lymph node, it was observed a greater expression of inflammatory cytokines IFN- ɣ, TNF- α and IL -6 and the enzyme arginase, 30 and 60 d.p.i., and it was corroborated by histological changes observed in the ear, intenser inflammatory process and chronicity of the disease. On the contrary, the popliteal lymph node (paw) presented a combination of pro and anti-inflammatory cytokines indicating a precocious regulation of immune and inflammatory response. It was also observed that the bigger the inoculum, the more intense the inflammatory response and bigger the lesions, however, without parasite dissemination to the liver and spleen, indicating lesser systemic commitment and increased survival time of the animal. In short, the data indicates that the inoculum of 105 parasites through the ear dermis infection model could make easier the visualization of a possible protective effect of new drugs or vaccine candidates.