Parasite load, iNOS and cytokine profiles, and histopathological aspects of Leishmania infantum infection in dogs with different clinical presentations

ABSTRACT: Visceral leishmaniasis (VL) is a zoonotic disease with a canine urban reservoir in South America. Dogs from an endemic area within Brazil, which were naturally infected with Leishmania infantum, and those presenting severe clinical (SC), mild, or no clinical (MNC) disease, were evaluated. Parasite load, histopathology, and cytokine and iNOS mRNA expressions were assessed in the spleen and liver in order to determine the potential markers for disease susceptibility or resistance. As a result, dogs with both SC and MNC had high parasite loads; IFN-γ was the most expressive cytokine in both organs, along with IL-6 and IL-4 being detected in the spleen and liver, and IL-10 only in liver. The hepatic tissue presented higher medians for IFN-γ and IL-10, and was the main organ to produce cytokines with hepatic IL-10 suggesting a regulatory follow up. Granulomas were detected in both organs; however, when absent in spleen, they were associated with elevated IL-6 levels, thus highlighting the anti-inflammatory role of IL-6. Microscopic lesions in the spleen were predominantly characterized by an extensively disorganized white pulp and splenic response was suggested as sub optimized. Parasite load, tissue damage, and immunological response may vary in the dogs with similar clinical symptoms, which may not be a good parameter for assessing the animal’s susceptibility to VL.

摘要：内脏利什曼病（Visceral leishmaniasis, VL）是一种在南美洲以城市犬类为储存宿主的人畜共患病。本研究对巴西流行区自然感染婴儿利什曼原虫（Leishmania infantum）的犬只进行分组评估，将其分为重度临床症状（SC）、轻度或无临床症状（MNC）组。通过检测脾脏与肝脏中的寄生虫载量、组织病理学特征，以及细胞因子与诱导型一氧化氮合酶（inducible nitric oxide synthase, iNOS）mRNA的表达水平，旨在筛选疾病易感或抵抗的潜在标志物。结果显示，重度临床症状组与轻度/无临床症状组犬只的寄生虫载量均处于较高水平；干扰素-γ（IFN-γ）是两种器官中表达最为显著的细胞因子，脾脏与肝脏中均可检出白细胞介素-6（IL-6）与白细胞介素-4（IL-4），而白细胞介素-10（IL-10）仅在肝脏中被检测到。肝脏组织中IFN-γ与IL-10的中位数水平更高，且肝脏是主要的细胞因子产生器官，其中肝脏IL-10提示存在免疫调控过程。两种器官均检出肉芽肿病变；但若脾脏未出现肉芽肿，则与IL-6水平升高相关，这进一步凸显了IL-6的抗炎作用。脾脏的显微病变主要表现为白髓广泛紊乱，提示其免疫应答未达最优状态。具有相似临床症状的犬只，其寄生虫载量、组织损伤程度及免疫应答模式存在差异，因此临床症状或许并非评估犬只内脏利什曼病易感性的可靠参数。