Control of pathogenic CD8+ T cell migration to the brain by IFN-gamma during experimental cerebral malaria.

Previous studies have shown that IFN-gamma is essential for the pathogenesis of cerebral malaria (CM) induced by Plasmodium berghei ANKA (PbA) in mice. However, the exact role of IFN-gamma in the pathway (s) leading to CM has not yet been described. Here, we used 129P2Sv/ev mice which develop CM between 7 and 14 days post-infection with PbA. In this strain, both CD4(+) and CD8(+) T cells were involved in the effector phase of CM. When 129P2Sv/ev mice deficient in the IFN-gamma receptor alpha chain (IFN-gammaR1) were infected with PbA, CM did not occur. Migration of leucocytes to the brain at the time of CM was observed in wild type (WT) but not in deficient mice. However, in the latter, there was an accumulation of T cells in the lungs. Analysis of chemokines and their receptors in WT and in deficient mice revealed a complex, organ-specific pattern of expression. Up-regulation of RANTES/CCL5, IP-10/CCL3 and CCR2 was associated with leucocyte migration to the brain and increased expression of MCP-1/CCL2, IP-10/CCL3 and CCR5 with leucocyte migration to the lung. This shows that IFN-gamma controls trafficking of pathogenic T cells in the brain, thus providing an explanation for the organ-specific pathology induced by PbA infection.

Experimental models of cerebral malaria.

Malaria remains a major global health problem and cerebral malaria is one of the most serious complications of this disease. Recent years have seen important advances in our understanding of the pathogenesis of cerebral malaria. Extensive analysis of tissues and blood taken from patients with cerebral malaria has been complimented by the use of animal models to identify specific components of pathogenic pathways. In particular, an important role for CD8+ T cells has been uncovered, as well divergent roles for members of the tumor necrosis factor (TNF) family of molecules, including TNF and lymphotoxin alpha. It has become apparent that there maybe more than one pathogenic pathway leading to cerebral malaria. The last few years have also seen the testing of vaccines designed to target malaria molecules that stimulate inflammatory responses and thereby prevent the development of cerebral malaria. In this review, we will discuss the above advancements, as well as other important findings in research into the pathogenesis of cerebral malaria. As our understanding of pathogenic responses to Plasmodium parasites gathers momentum, the chance of a breakthrough in the development of treatments and vaccines to prevent death from cerebral malaria have become more realistic.

Stage-specific transcription of distinct repertoires of a multigene family during Plasmodium life cycle.

Members of a multigene family in the rodent malaria parasite Plasmodium yoelii yoelii code for 235-kilodalton proteins (Py235) that are located in the merozoite apical complex, are implicated in virulence, and may determine red blood cell specificity. We show that distinct subsets of py235 genes are expressed in sporozoites and hepatic and erythrocytic stages. Antibodies to Py235 inhibited sporozoite invasion of hepatocytes. The switch in expression profile occurred immediately after transition from one stage to another. The results suggest that this differential expression is driven by strong biological requirements and provide evidence that hepatic and erythrocytic merozoites differ.

Inhibition of Plasmodium yoelii blood-stage malaria by interferon alpha through the inhibition of the production of its target cell, the reticulocyte.

The effect of a recombinant hybrid human interferon alpha (IFN-alpha) (which cross-reacts with murine cells) on C57BL/6 mice infected with Plasmodium yoelii sporozoites or parasitized erythrocytes was determined. IFN-alpha did not inhibit the development of the parasite in the liver, but it did reduce the blood parasite load and the hepatosplenomegaly induced by the infection in mice injected with blood-stage parasites. The extent of anemia in IFN-alpha-treated and control mice was similar, despite the lower parasite load in the IFN-alpha-treated mice. The reduced blood parasite load in IFN-alpha-treated mice was associated with reduced erythropoiesis and reticulocytosis. As reticulocytes are the preferred target cells for the strain of P yoelii used (P yoelii yoelii 265 BY), it was postulated that the inhibition of reticulocytosis in IFN-alpha-treated mice was causally related to the observed decreased blood parasite load. This was supported by the finding that IFN-alpha inhibited a different strain of P yoelii (17X clone A), which also displays a tropism for reticulocytes, but not a line of Plasmodium vinckei petteri, which infects only mature red blood cells. As human malaria species also display different tropism for reticulocytes, these findings could be relevant for people coinfected with multiple Plasmodium species or strains or coinfected with Plasmodium and virus. (Blood. 2001;97:3966-3971)

Involvement of IFN-gamma receptor-medicated signaling in pathology and anti-malarial immunity induced by Plasmodium berghei infection.

IFN-gamma has been implicated in the pathogenesis of experimental cerebral malaria (ECM). We have used mice lacking the alpha chain of the IFN-gamma receptor (KO mice) to define its role in the pathogenesis of ECM. Infected KO mice did not develop ECM and showed no leukocyte or parasite sequestration in the brain, and no hemorrhages. The resistance of KO mice to ECM was associated with the absence of any increases of TNF-alpha and ICAM-1 proteins in the brain, which are both essential for ECM. Wild-type (WT) mice which do not develop ECM, despite increased local production of TNF-alpha protein, showed no leukocyte accumulation in the brain and this was correlated with the absence of ICAM-1 protein from brain microvessels. KO mice infected with 106 parasitized erythrocytes (PE) of Plasmodium berghei ANKA (PbA) did not develop ECM, but they had high parasitemia and died earlier than WT mice which did not develop ECM. However, KO mice did not develop higher parasitemia than WT mice when both groups were infected with a lower dose (5x10(5) PE) of PbA-infected red blood cells. This indicates that different doses of PE may trigger different IFN-gamma responses and that there may be a threshold concentration for protection against parasitemia.