Date Published: June 14, 2018
Publisher: Public Library of Science
Author(s): Haruka Mizobuchi, Wataru Fujii, Shoko Isokawa, Kanna Ishizuka, Yihan Wang, Sayoko Watanabe, Chizu Sanjoba, Yoshitsugu Matsumoto, Yasuyuki Goto, Partha Mukhopadhyay.
Hepatic dysfunction is one of the clinical features in severe malaria. However, the mechanism of hepatic injury during malaria is still unknown. Myeloid-related protein (MRP) 14 is abundantly expressed by myeloid cells and involved in various inflammatory diseases. We previously reported that serum MRP14 is elevated in mice infected with Plasmodium berghei ANKA. In order to verify whether extracellular MRP14 is involved in the pathology of hepatic injury during rodent malaria, we intravenously administrated recombinant MRP14 (rMRP14) to mice infected with P. berghei ANKA. The administration of rMRP14 did not affect parasite number or hematocrit. On the other hand, the hepatic injury was exacerbated in rMRP14-treated mice, and their serum concentration of hepatic enzymes increased significantly more than PBS-treated controls. Immunohistochemical analysis of the liver showed that more MRP14+ macrophages accumulated in rMRP14-treated mice than PBS-treated controls after infection. The administration of rMRP14 also promotes the up-regulation of pro-inflammatory molecules in the liver, such as iNOS, IL-1β, IL-12, and TNF-α. Even in the absence of Plasmodium infection, administration of rMRP14 could induce the accumulation of MRP14+ macrophages and up-regulation of the pro-inflammatory molecules in the liver of naïve mice. The results indicate that MRP14 promotes the accumulation of MRP14+ cells and the up-regulation of pro-inflammatory molecules and NO, which amplify inflammatory cascade leading to hepatic injury. In conclusion, MRP14 is a one of key molecules for liver inflammation during rodent malaria.
Hepatic dysfunction is one of the common clinical features in severe malaria patients. Severe liver dysfunction occurs occasionally in severe malaria in association with multi-organ failure and poor prognosis [1–3]. In adult non-immune patients in South-East Asia and India, jaundice and liver dysfunction occur in up to 50% of cases in severe malaria, almost always as part of multi-organ disease . Elevations of liver cytoplasmic enzymes are common, including raised aspartate aminotransferase (AST), alanine aminotransferase (ALT) and alkaline phosphatase [2,3]. Histopathological examination of liver biopsies of severe malaria patients showed that dilated sinusoids, parasitized red blood cell (pRBC) sequestration within hepatic sinusoids and adhesion of pRBCs to sinusoidal endothelial cells, and the retention of malaria pigment, accompanied with hepatocyte swelling and necrosis, host macrophage infiltration and focal centrilobular hepatic necrosis [1,4–6]. It is reported that the degree of jaundice, hepatomegaly and liver enzyme abnormalities correlates with the overall parasite load in the body, and the sequestration of pRBCs in the liver was quantitatively associated with liver weight, serum bilirubin and AST levels .
Previous reports showed that T cells and IFN-γ play a critical role in the protective immunity against non-lethal murine malarial strain, P. chabaudi or P. berghei XAT [27–29]. On the other hand, other reports demonstrated that T cells and IFN-γ are potentially involved in the pathogenesis during lethal rodent malarial strain, P. berghei NK65 or P. berghei ANKA [9,30,31]. In order to elucidate whether T cells are involved in the pathogenesis of hepatic injury during infection with P. berghei ANKA, T cell-deficient nu/nu mice were infected with Pb-pRBCs. It is revealed that hepatic injury during Pb-infection was induced through T cell-dependent mechanism regardless of parasite number. Cell stimulation assay indicates that Pb-pRBC antigen-specific T cells play a pivotal role in IFN-γ and iNOS production (Fig 1F and 1E). Besides, even though the number of MRP14+ cells was comparable between nu/nu mice and WT mice, the secretion of MRP14 is dependent on T cells (Figs 1D and 2A). The mechanism of MRP14 secretion has been unclear, and our study revealed that T cell is associated to one side of the MRP14 secretion mechanism. There was a positive correlation between serum concentration of hepatic enzymes and MRP14 (Figs 1D and 2A). This relation between hepatic injury and serum MRP14 level indicates that extracellular MRP14 has some functions involved in the pathogenesis of hepatic injury during rodent malaria. Considering that both MRP14+ cells and T cells were present with the increased number in the liver during Pb-infection (Fig 2C), it is suggested that MRP14 assists the function of T cells to induce nitric oxide (NO) through IFN-γ in the liver during rodent malaria. We observed that rMRP14 promoted NO production from RAW264.7 cells stimulated with IFN-γ (data not shown), which suggests that MRP14 potentiates IFN-γ-induced NO production. Because high levels of NO, generated primarily by iNOS, have cytotoxic and pro-inflammatory effects leading to severe hepatic injury [32,33], MRP14 seems to promote hepatic injury by increasing NO production during rodent malaria. Interestingly, MRP14+ cells were accumulated in the liver during Pb-infection in both of nu/nu and WT mice, suggesting a T cell-independent mechanism for accumulating MRP14+ cells during Pb-infection.