Pathology of Plasmodium chabaudi chabaudi infection and mortality in interleukin-10-deficient mice are ameliorated by anti-tumor necrosis factor alpha and exacerbated by anti-transforming growth factor beta antibodies

Abstract

Interleukin-10 (IL-10)-deficient (IL-10(-/-)) mice infected with Plasmodium chabaudi (AS) suffer a more severe disease and exhibit a higher rate of mortality than control C57BL/6 mice. Here, we show that a drop in body temperature to below 28 degrees C and pronounced hypoglycemia of below 3 mM are reliable indicators of a lethal infection. Elevated inflammatory responses have been shown to accompany pathology in infected IL-10(-/-) mice. We show that neutralization of tumor necrosis factor alpha (TNF-alpha) in IL-10(-/-) mice abolishes mortality and ameliorates the hypothermia, weight loss, and anemia but does not affect the degree of hypoglycemia. These data suggest that TNF-alpha is involved in some of the pathology associated with a P. chabaudi infection in IL-10(-/-) mice but other factors play a role. IL-10(-/-) mice that survive a primary infection have been shown to control gamma interferon (IFN-gamma) and TNF-alpha production, indicating that other cytokines or mechanisms may be involved in their down-regulation. Significantly higher levels of transforming growth factor beta (TGF-beta), a cytokine with such properties, are present in the plasma of infected IL-10(-/-) mice at a time that coincides with the disappearance of IFN-gamma and TNF-alpha from the blood. Neutralization of TGF-beta in IL-10(-/-) mice resulted in higher circulating amounts of TNF-alpha and IFN-gamma, and all treated IL-10(-/-) mice died within 12 days with increased pathology but with no obvious increase in parasitemia. Our data suggest that a tight regulation of the balance between regulatory cytokines such as IL-10 and TGF-beta and inflammatory cytokines such as IFN-gamma and TNF-alpha is critical for survival in a mouse malaria infection.

FIG. 1.

Comparison of pathological changes between IL-10^−/− mice that succumbed to infection (•, n = 25) and those that survived (○, n = 29). The distribution of the percentage of body weight loss (A), body temperature (B), blood glucose concentration (C), and percentage of packed red cell volume (D) are shown for each individual mouse.

FIG. 2.

Course of parasitemia (A), survival rate (B) and pathological changes (C to F) of IL-10^−/− mice treated with anti-TNF-α (▪) or control IgG antibodies (□) during a primary erythrocytic-stage P. chabaudi infection. Parasitemias are presented as the geometric means ± standard errors of the means of pooled data from 32 mice from four independent experiments. Body weight (C), blood glucose concentration (D), temperature (E), and hematocrit (F) changes were measured during the course of infection as described in the text. These graphs show means ± standard errors of the means of the values for 32 mice pooled from four independent experiments. Standard errors of the means of less than 10% of the means are not shown. *, significant differences are observed between two groups of mice.

FIG. 3.

Concentrations of IFN-γ (A) and TNF-α (B) in the plasma of individual IL-10^−/− mice treated with either anti-TNF-α (▪, n = 5) or control IgG (□, n = 5) during the course of a primary P. chabaudi infection. Each point represents data from one animal.

FIG. 4.

Concentration of TGF-β in the plasma of IL-10^−/− (•) and WT (○) mice during a primary P. chabaudi infection. (A) Experiment 1, 5 mice per group; (B) experiment 2, 15 mice per group. Each data point represents one animal. *, significant differences between the two groups of mice. The horizontal line on each graph represents the amount of TGF-β in uninfected control plasma.

FIG. 5.

Survival rate and pathological changes in IL-10^−/− mice treated with anti-TGF-β antibody (▪, n = 10) or control IgG (□, n = 10) during a primary P. chabaudi infection. The data represent the means ± standard errors of the means of two independent experiments, with a total of 10 mice. Standard errors of the means of less than 10% of the mean are not shown. Representative levels of IFN-γ and TNF-α in plasma on day 8 in IL-10^−/− mice treated with anti-TGF-β antibody (▪) or control IgG (□) are shown. Each bar represents an individual mouse. *, significant differences between the two groups of mice.