Characterization of cerebral malaria in the outbred Swiss Webster mouse infected by Plasmodium berghei ANKA

Abstract

Plasmodium berghei ANKA (PbA) infection in susceptible inbred mouse strains is the most commonly used experimental model to study pathogenesis of cerebral malaria (CM). Indeed, many concepts on mechanisms related to this complication have arisen from works using this model. Although inbred strains present several advantages and are indicated for most studies, the use of outbred models can show unique usefulness in a number of approaches such as fine post-quantitative trait loci mapping and discovery of genes relevant to CM susceptibility or resistance, as well as pharmacological and vaccine studies. Here we describe the features of PbA infection and CM incidence, and characterize the associated multiorgan pathology in the outbred Swiss Webster mouse. This model showed a sizeable (62.7%) and reproducible incidence of CM demonstrated by clinical signs and histopathological changes in brain (microhaemorrhages, oedema and vessel plugging by mononuclear cells). Major pathological changes were also observed in lungs, liver, thymus and spleen, analogous to those observed in inbred strains. Parasitaemia levels were associated with the risk of CM development, the risk being significantly higher in mice showing higher values of parasitaemia on days 6-7 of infection. This outbred CM model is then suitable for genetic, vaccine and drug studies targeting this malaria complication.

Figure 1

Survival curve (a) and course of parasitaemia (b) of Swiss Webster and CBA mice infected with 1 × 10⁶Plasmodium berghei ANKA-parasitized red blood cells. CM, mice with cerebral malaria; no-CM, mice that did not develop cerebral malaria. Results are expressed as means ± SEM.

Figure 2

Brain and liver of Swiss Webster mice. (a) Panoramic view of non-infected control mouse brain with a clean large vessel. Haematoxylin–eosin, 200×. (b) Infected mouse, large haemorrhage in cerebellum, Purkinje cell area. Haematoxylin–eosin, 400×. (c) Infected mouse, brain vessel full of pigment-containing monocytes. Parasitized and non-parasitized RBC can be observed adherent to activated monocytes. Haematoxylin–eosin, 500×. (d) Panoramic view of a normal mouse liver, showing typical architecture, clean sinusoids and resting Kupffer cells. Haematoxylin–eosin, 200×. (e) Infected mouse, moriform vacuolization of hepatocytes and pigmented Kupffer cells. Haematoxylin–eosin, 200×. (f) Detail of moriform vacuolization, hypertrophic Kupffer cells containing malarial pigment and intra-sinusoidal clusters of mononuclear cells. Haematoxylin–eosin, 400×.

Figure 3

Lungs and thymus of Swiss Webster mice. (a) Panoramic view of non-infected control mouse lung with thin alveoli walls and clean blood vessels. Haematoxylin–eosin, 200×. (b) Panoramic view of the lung of an infected mouse, showing thickening of alveoli walls by the infiltration of mononuclear and polymorphonuclear cells. Haematoxylin–eosin, 200×. (c) Detail of septal thickening in an infected mouse lung, showing predominance of mononuclear cells. Haematoxylin–eosin, 400×. (d) Panoramic view of a normal mouse thymus, showing the cortical area plenty of thymocytes and the internal medullar area with a lower cellularity. Giemsa, 200×. (e) Panoramic view of the thymus of a infected mouse, showing intense thymocyte depletion in the cortical area, with only a few remaining thymocytes between the framework of epithelial cells, and an increase in the medullar cellularity resulting in cortico-medullar inversion. Giemsa, 200×. (f) Pronounced monocyte adherence on the endothelium of thymus medullary vessels of infected mice. Monocytes look like macrophages and contain malarial pigment. Giemsa, 1000×.

Figure 4

Spleen of Swiss Webster mice. (a) Panoramic view of non-infected control mouse spleen. White and red pulps with well-defined limits. One B-cell resting follicle with surrounding thick marginal zones. Giemsa, 200×. (b) Panoramic view of infected mouse spleen. Disorganized germinal centre with intense centroblast activation, proliferation, apoptosis, without centrocyte differentiation and definition of light and dark areas, absence of marginal zone and blurred limits between white and red pulps. Giemsa, 200×. (c) T-cell area (periarteriolar lymphoid sheath) of infected mouse. Centroblasts. Giemsa, 400×. (d) Infected mouse, malarial pigment in red pulp macrophages. Giemsa 400×.