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Mice deficient of functional interferon regulatory factor-1 (IRF-1-/-) by targeted gene disruption infected with a lethal murine malaria strain, Plasmodium berghei ANKA survived longer than its wild-type littermates despite the inability to induce appreciable amounts of interferon-gamma (IFN-gamma) and nitric oxide. In addition, infected IRF-1-/- mice displayed less organ injury with reduced necrosis and inflammation. Both wild-type and IRF-1-/- mice treated with exogenous interleukin-12 (IL-12) suffered extensive organ damage with corresponding up regulation of IFN-gamma, suggesting the pathogenic potential of IL-12 and IFN-gamma. IL-10 is a cytokine produced by CD4+ T lymphocytes belonging to the Th2 subset. Expression of IL-10 in the wild-type mice correlated with the severity of the infection, with higher mRNA expression towards the later stage of infection. In contrast to the wild-type mice, IL-10 levels in the IRF-1-/- mice were induced early in the infection and decreased gradually as the infection progressed. Both untreated and IL-12 treated wild-type mice appeared to follow a Th1-like immune response early in the infection and a Th2-like immune response later in the infection. However, the IRF-1-/- mice were able to launch an altered immune response with a Th2-like immune response early in the infection. These findings suggest that IL-10 expression in the IRF-1-/- mice during the early stage of P. berghei ANKA infection could play an important role in suppressing pathogenic effects of a cell mediated immune response and promoting protective immunity against the parasite.

Malaria infections often cause glomerulonephritis (GN), and multiple factors have been implicated in the pathogenesis of glomerular injury. The role of cytokines in malaria associated glomerulonephritis has not been clearly defined. To study the importance of cytokines in malarial nephritis, we investigated the expression of tumour necrosis factor-alpha (TNF-alpha), interleukin-1alpha (IL-1alpha), IL-6, IL-10 and granulocyte macrophage-colony stimulating factor (GM-CSF) in kidneys acutely infected with murine malaria parasite Plasmodium berghei ANKA in C57BL/6 J mice. Groups of six mice sacrificed on days 5, 8-10, 15, and 20 postinfection, and normal controls were used for cytokine analysis. Elevated levels of messenger RNA (mRNA) specific for these cytokines in infected kidneys after day 5 postinfection were demonstrated by reverse transcription-polymerase chain reaction (RT-PCR) analysis. Kidney sections stained with specific antibodies against TNF-alpha, IL-1alpha, IL-6, IL-10 and GM-CSF by immunohistochemistry showed that the staining for these cytokines on the glomeruli was positive from day 10 postinfection, and increased progressively, mainly in the infiltrating macrophages and the glomerular mesangium. Strong correlation was found between the expression of TNF-alpha with IL-6, and IL-1alpha with IL-6. The expression of TNF-alpha, IL-1alpha, IL-6, and IL-10 also strongly correlated with the severity of proteinuria. Our findings show that there is up-regulation of cytokines in the pathogenesis of glomerulonephritis associated with murine malaria infection.