Susceptibility to experimental cerebral malaria induced by Plasmodium berghei ANKA in inbred mouse strains recently derived from wild stock

Abstract

The neurological syndrome caused by Plasmodium berghei ANKA in rodents partially mimics the human disease. Several rodent models of cerebral malaria (CM) exist for the study of the mechanisms that cause the disease. However, since common laboratory mouse strains have limited gene pools, the role of their phenotypic variations causing CM is restricted. This constitutes an obstacle for efficient genetic analysis relating to the pathogenesis of malaria. Most common laboratory mouse strains are susceptible to CM, and the same major histocompatibility complex (MHC) haplotype may exhibit different levels of susceptibility. We analyzed the influence of the MHC haplotype on overcoming CM by using MHC congenic mice with C57BL/10 and C3H backgrounds. No correlation was found between MHC molecules and the development of CM. New wild-derived mouse strains with wide genetic polymorphisms were then used to find new models of resistance to CM. Six of the twelve strains tested were resistant to CM. For two of them, F(1) progeny and backcrosses performed with the reference strain C57BL/6 showed a high level of heterogeneity in the number and characteristics of the genetic factors associated with resistance to CM.

FIG. 1.

(A) Histopathological studies show typical microvessels with adherent leukocytes (arrow). (B) Evans Blue leakage analysis was performed for control, CM⁺, and CM⁺⁺⁺ C57BL/6 mice infected P. berghei ANKA. CM⁺ and CM⁺⁺⁺ nomenclature was used to define degrees of severity of the neurological syndrome. As exemplified in the picture, CM⁺ mice showed mild symptoms, whereas CM⁺⁺⁺ mice were at the latest stage of the disease.

FIG. 2.

Effects of the genetic background and the MHC haplotype of the host on the incidence of CM. (A) Bar charts show the percentage of mortality from CM of some common strains of laboratory mice: C57BL/6 (n = 19), O129/Sv (n = 12), BALB/c (n = 25), and DBA/2 (n = 25). (B) CM mortality was also studied for MHC congenic C57BL/10 strains (5 to 41 mice per strain). (C) The same study was repeated on MHC congenic C3H strains (5 to 16 mice per strain).

FIG. 3.

Determination of CM susceptibility for three strains belonging to M. musculus musculus. (A) Survival curves for strains MAI (⧫; 10 females and 9 males), MBT (▪; 10 females and 10 males), and PWK (▴; 14 females and 16 males). The shaded portion represents the time window of mortality from CM for the strains tested. (B) Parasitemia was determined for strains MAI (five males and four females), MBT (five females and five males), and PWK (eight females and six males). Bar charts represent the mean percentage of parasitemia ± the standard deviation. The survival curve (○) and parasitemia of C57BL/6 are included as a reference.

FIG. 4.

Determination of CM susceptibility for four M. musculus subsp. domesticus strains. (A) Survival curves were constructed for strains 38CH (♦) (4 females and 12 males), BIK/g (▪; 14 females and 17 males), WLA (▴; 11 females and 10 males), and WMP (•; 27 females and 22 males). The shaded portion represents the time window of mortality from CM, which occurred only in WMP and C57BL/6 strains. (B) Parasitemia was determined for strains 38CH (five males), BIK/g (five females and three males), WLA (five females and five males), and WMP (five females and five males). Bar charts represent the mean percentage of parasitemia ± the standard deviation. The survival curve (○) and parasitemia of C57BL/6 are included as a reference.

FIG. 5.

Study of CM susceptibility of M. musculus castaneus (CAST/Ei). (A) Survival curve (▴) and parasitemia (B) were determined with 17 female mice. The shaded portion represents the time window of mortality from CM. Bar charts represent the mean percentage of parasitemia ± the standard deviation. The survival curve (○) and parasitemia of C57BL/6 mice are included as reference.

FIG. 6.

CM susceptibility of three strains belonging to M. spretus. (A) Survival curves were determined for strains SEG (▴; 20 females and 10 males), SPRET/Ei (⧫; 7 females and 3 males), and STF (▪; 39 females and 31 males). (B) Parasitemia was determined for strains SEG (5 females and 3 males), SPRET/Ei (4 females and 5 males), and STF (9 females and 13 males). Bar charts represent the mean percentage of parasitemia ± the standard deviation. The survival curve (○) and parasitemia of C57BL/6 mice are included as reference. The shaded portion represents the time window of mortality from CM for C57BL/6 strain.

FIG. 7.

CM susceptibility of ZYD (M. spicilegus). (A) The survival curve (▴) and parasitemia (B) were determined with 17 females. The shaded portion in panel A represents the time window of mortality from CM. Bar charts represent the mean percentage of parasitemia ± the standard deviation. The survival curve (○) and parasitemia of C57BL/6 mice are included as reference.

FIG. 8.

Susceptibility to CM exhibited by (CM-resistant strain × C57BL/6)F₁ progenies. Survival curves for F₁ crosses with C57BL/6 were performed with strains 38CH (A), BIK/g (B), and WLA (C). A cross between a male from a resistant strain and a female C57BL/6 mouse is indicated by a triangle, and the opposite cross is indicated by a square. Experiments were performed with 45 females and 48 males for (38CH × B6)F₁, 26 females and 28 males for (BIK/g × B6)F₁, 7 females and 8 males for (B6 × BIK/g)F₁, 13 females and 18 males for (WLA × B6)F₁, and 8 females for (B6 × WLA)F₁. The survival curve (○) of C57BL/6 mice is included as reference. The shaded portion represents the time window of mortality from CM.

FIG. 9.

CM susceptibility of mice resulting from (38CH × B6)F₁ progeny backcrossed with 38CH mice (A) and from (WLA × B6)F₁ progeny backcrossed with C57BL/6 mice (B). The survival curves for these mice are represented by triangles. The survival curve (○) and parasitemia of C57BL/6 mice are included as a reference. The shaded portions represent death from CM.