Comparison of pathology in susceptible A/J and resistant C57BL/6J mice after infection with different sub-strains of Plasmodium chabaudi

Differential roles of inflammation and apoptosis in initiation of mid-gestational abortion in malaria-infected C57BL/6 and A/J mice

INTRODUCTION

Plasmodium chabaudi AS-infection in pregnant A/J and C57BL/6J mice results in mid-gestational pregnancy loss. Although associated with increased systemic and placental pro-inflammatory responses and coagulopathy, the molecular mechanisms that underlie poor pregnancy outcomes in these mice are not yet fully understood. This study investigates the relationships between inflammation, apoptosis and malaria-induced pregnancy loss.

METHODS

Infection with P. chabaudi AS in early murine pregnancy and term human placental tissues from an endemic setting were assessed by histology, immunohistochemistry, TUNEL staining, real-time PCR, flow cytometry, western blot, and ELISA.

RESULTS

Quantitative PCR reveals accumulation of lymphocytes and monocytes and upregulation of chemokines that attract these cell types in malaria-exposed mid-gestational A/J conceptuses. Monocyte accumulation is confirmed by flow cytometry and placental immunohistochemistry. Concurrent with initiation of malaria-induced abortion, markers of apoptosis are evident in the junctional zone, but not the labyrinth, of A/J placentae. In contrast, mid-gestation conceptuses in infected C57BL/6J lack evidence for monocyte accumulation, exhibiting low or no in situ placental staining despite trophoblast immunoreactivity for the monokine, CCL2. Additionally, placental apoptosis is not consistently observed, and when evident, appears after malaria-induced abortion typically initiates. Similarly, trophoblast apoptosis in term human placental malaria is not observed. Of those studied, a sole common feature of malaria-induced abortion in A/J and C57BL/6J mice is elevation of plasma tumor necrosis factor.

DISCUSSION

Consistent with our previous observations, tumor necrosis factor is likely to be a central driver of malaria-induced pregnancy loss in both strains, but likely operates through mechanisms distinct from placental apoptosis in C57BL/6J mice.

Predictive criteria to study the pathogenesis of malaria-associated ALI/ARDS in mice

Malaria-associated acute lung injury/acute respiratory distress syndrome (ALI/ARDS) often results in morbidity and mortality. Murine models to study malaria-associated ALI/ARDS have been described; we still lack a method of distinguishing which mice will develop ALI/ARDS before death. This work aimed to characterize malaria-associated ALI/ARDS in a murine model and to demonstrate the first method to predict whether mice are suffering from ALI/ARDS before death. DBA/2 mice infected with Plasmodium berghei ANKA developing ALI/ARDS or hyperparasitemia (HP) were compared using histopathology, PaO₂ measurement, pulmonary X-ray, breathing capacity, lung permeability, and serum vascular endothelial growth factor (VEGF) levels according to either the day of death or the suggested predictive criteria. We proposed a model to predict malaria-associated ALI/ARDS using breathing patterns (enhanced pause and frequency respiration) and parasitemia as predictive criteria from mice whose cause of death was known to retrospectively diagnose the sacrificed mice as likely to die of ALI/ARDS as early as 7 days after infection. Using this method, we showed increased VEGF levels and increased lung permeability in mice predicted to die of ALI/ARDS. This proposed method for accurately identifying mice suffering from ALI/ARDS before death will enable the use of this model to study the pathogenesis of this disease.

Host susceptibility to malaria in human and mice: compatible approaches to identify potential resistant genes

There is growing evidence for human genetic factors controlling the outcome of malaria infection, while molecular basis of this genetic control is still poorly understood. Case-control and family-based studies have been carried out to identify genes underlying host susceptibility to malarial infection. Parasitemia and mild malaria have been genetically linked to human chromosomes 5q31-q33 and 6p21.3, and several immune genes located within those regions have been associated with malaria-related phenotypes. Association and linkage studies of resistance to malaria are not easy to carry out in human populations, because of the difficulty in surveying a significant number of families. Murine models have proven to be an excellent genetic tool for studying host response to malaria; their use allowed mapping 14 resistance loci, eight of them controlling parasitic levels and six controlling cerebral malaria. Once quantitative trait loci or genes have been identified, the human ortholog may then be identified. Comparative mapping studies showed that a couple of human and mouse might share similar genetically controlled mechanisms of resistance. In this way, char8, which controls parasitemia, was mapped on chromosome 11; char8 corresponds to human chromosome 5q31-q33 and contains immune genes, such as Il3, Il4, Il5, Il12b, Il13, Irf1, and Csf2. Nevertheless, part of the genetic factors controlling malaria traits might differ in both hosts because of specific host-pathogen interactions. Finally, novel genetic tools including animal models were recently developed and will offer new opportunities for identifying genetic factors underlying host phenotypic response to malaria, which will help in better therapeutic strategies including vaccine and drug development.

Gut microbiota, tight junction protein expression, intestinal resistance, bacterial translocation and mortality following cholestasis depend on the genetic background of the host

Failure of the intestinal barrier is a characteristic feature of cholestasis. We have previously observed higher mortality in C57BL/6J compared with A/J mice following common bile duct ligation (CBDL). We hypothesized the alteration in gut barrier function following cholestasis would vary by genetic background. Following one week of CBDL, jejunal TEER was significantly reduced in each ligated mouse compared with their sham counterparts; moreover, jejunal TEER was significantly lower in both sham and ligated C57BL/6J compared with sham and ligated A/J mice, respectively. Bacterial translocation to mesenteric lymph nodes was significantly increased in C57BL/6J mice vs. A/J mice. Four of 15 C57BL/6J mice were bacteremic; whereas, none of the 17 A/J mice were. Jejunal IFN-γ mRNA expression was significantly elevated in C57BL/6J compared with A/J mice. Western blot analysis demonstrated a significant decrease in occludin protein expression in C57BL/6J compared with A/J mice following both sham operation and CBDL. Only C57BL/6J mice demonstrated a marked decrease in ZO-1 protein expression following CBDL compared with shams. Pyrosequencing of the 16S rRNA gene in fecal samples showed a dysbiosis only in C57BL/6J mice following CBDL when compared with shams. This study provides evidence of strain differences in gut microbiota, tight junction protein expression, intestinal resistance and bacterial translocation which supports the notion of a genetic predisposition to exaggerated injury following cholestasis.

Plasmodium chabaudi AS induces pregnancy loss in association with systemic pro-inflammatory immune responses in A/J and C57BL/6 mice

The molecular mechanisms that underlie poor birth outcomes in malaria during pregnancy remain poorly defined. To assess the role of host immune responses, mice known to respond differentially to Plasmodium chabaudi AS infection were studied. Following infection at day 0 of pregnancy, A/J mice developed significantly higher parasitemia than C57BL/6 (B6) mice and succumbed to infection. Both strains had evidence of parasite accumulation in the placenta at mid-gestation and aborted, with significantly higher embryo loss in infected A/J mice on day 9. While infection-induced systemic tumour necrosis factor (TNF) and interleukin (IL)-1β in the latter were significantly higher at day 11, day 10 IL-10 levels were higher in B6 mice. No differences in the levels of splenic lymphocyte subsets, neutrophils or monocytes between infected pregnant A/J and B6 mice were observed, with most cell types expanding in response to infection regardless of pregnancy. Antibody ablation of TNF exacerbated infection in A/J mice and did not ameliorate pregnancy outcome. Thus, malaria induces poor pregnancy outcome in both the mouse strains in the context of quantitatively different systemic inflammatory responses. Further evaluation of the roles of soluble and cellular immune components, particularly at the uteroplacental level, will be required to define the most critical pregnancy-compromising mechanisms.

Pathology of Tnf-deficient mice infected with Plasmodium chabaudi adami 408XZ

Tumor necrosis factor alpha (Tnf) plays a pleiotropic role in murine malaria. Some investigations have correlated Tnf with hypothermia, hyperlactatemia, hypoglycemia, and a suppression of the erythropoietic response, although others have not. In this study, we have evaluated parasitemia, survival rate and several pathological features in C57BL/6JTnf(-/-) and C57BL/6JTnf(+/+) mice after infection with Plasmodium chabaudi adami 408XZ. Compared to the C57BL/6JTnf(+/+) mice, C57BL/6JTnf(-/-) mice showed increased parasitemia and decreased survival rate, whereas blood glucose, blood lactate and body weight were not significantly different. However, C57BL/6JTnf(-/-) mice suffered significantly more from severe anemia and hypothermia than C57BL/6JTnf(+/+) mice. These results suggest that Tnf is an important mediator of parasite control, but not of anemia development. We hypothesize that the high mortality observed in the Tnf knock-out mice is due to increased anemia and pathology as a direct result of increased levels of parasitemia.