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）是一种在南美洲存在城市犬类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）的犬只进行了评估，这些犬只分别表现为重度临床症状（SC）、轻度临床症状或无临床症状（MNC）。为筛选疾病易感性或抗性的潜在标志物，研究人员对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信使核糖核酸（iNOS mRNA）的表达水平进行了检测。研究结果显示，表现重度临床症状与无/轻度临床症状的犬只均呈现较高的寄生虫载量；干扰素-γ（IFN-γ）是两种器官中表达最显著的细胞因子，白细胞介素6（IL-6）与白细胞介素4（IL-4）可在脾脏与肝脏中检出，而白细胞介素10（IL-10）仅在肝脏中被检测到。肝脏组织中干扰素-γ与白细胞介素10的表达中位数更高，且是主要的细胞因子产生器官，肝脏中的白细胞介素10提示存在免疫调控过程。两种器官中均检测到肉芽肿；但若脾脏未出现肉芽肿，则与白细胞介素6水平升高相关，这进一步凸显了白细胞介素6的抗炎作用。脾脏的微观病变主要表现为白髓广泛紊乱，提示脾脏免疫应答处于亚优化状态。感染相似临床症状的犬只，其寄生虫载量、组织损伤程度与免疫应答水平存在差异，因此临床症状或并非评估犬只感染内脏利什曼病易感性的可靠指标。