We explored the role of CD40-CD40L (CD154) in the severe malaria elicited by Plasmodium berghei anka infection in mice. Mortality was >90% by day 8 after infection in ؉/؉ mice, but markedly decreased in CD40؊/؊ or in CD40L؊/؊ mice, as well as in ؉/؉ mice treated with anti-CD40L monoclonal antibody. Parasitemia was similar in the different conditions. Breakdown of the blood-brain barrier was evident in infected ؉/؉, but not in CD40؊/؊ mice. Thrombocytopenia was less severe in CD40؊/؊ mice than in the ؉/؉ controls. Sequestration of macrophages in brain venules and alveolar capillaries was reduced in CD40؊/؊ or in CD40L؊/؊ mice, whereas sequestration of parasitized red blood cells or polymorphonuclear leukocytes in alveolar capillaries was CD40-CD40L-independent. CD40 mRNA was increased in the brain and lung of infected mice whereas CD40L was increased in the lung. Tumor necrosis factor plasma levels were similarly increased in infected ؉/؉ or CD40؊/؊ mice. Expression of CD54 and its mRNA levels in the brain were moderately decreased in CD40-deficient mice. Thus the mortality associated with severe malaria requires CD40-CD40L interaction that contributes to the breakdown of the blood-brain barrier, macrophage sequestration, and platelet consumption.

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SUMMARY:Infection of susceptible mice with Plasmodium berghei Anka leads to a syndrome of severe or cerebral malaria.Tumor necrosis factor (TNF) contributes to this syndrome, apparently by acting on its receptor 2 (TNFR2) because TNFR1-/-are susceptible, whereas TNFR2-/-mice are resistant. In this work, we confirmed the essential role of the TNFR2 in cerebral malaria because 6 to 8 days after Plasmodium berghei Anka infection, hypothermia, coma, and death were observed in ϩ/ϩ or TNFR1-/-, but never in TNFR2-/-, mice. TNF production, evaluated by the serum levels or the mRNA levels in the brain, spleen or lung, was similar in ϩ/ϩ, TNFR1-/-, or TNFR2-/-mice. Macrophage or parasitized red blood cell sequestration in brain or lung was similar in TNFR1-/-and TNFR2-/-mice. Accordingly, up-regulation of CD54 or CD40 in brain or lung was also similar in TNFR1-/-or TNFR2-/-mice. Platelet loss, manifested by thrombocytopenia and the presence of microparticles in plasma, was similar in TNFR1-/-or TNFR2-/-mice. Breakdown of the blood-brain barrier, detected by the diffusion of tracers, was attenuated in both TNFR1-/-and TNFR2-/-, compared with ϩ/ϩ, mice. Endothelial cells from brain capillaries, examined by transmission electron microscopy, were similar in infected TNFR1-/-or TNFR2-/-mice, whereas the basement membrane was enlarged in TNFR1-/-mice. Hypothermic mice were also hyperglycemic, and this was evident in ϩ/ϩ and TNFR1-/-, but not in TNFR2-/-, mice. In addition, infected ϩ/ϩ and TNFR1-/-mice became insulin resistant, while in contrast TNFR2-/-became extremely insulin sensitive. This study supports the possibility that coma and death are mediated not by cell sequestration or breakdown of vascular permeability, similar in TNFR1-/-or TNFR2-/-mice, but by metabolic disturbances selectively mediated by the TNFR2. (Lab Invest 2002, 82:1155-1166.

Infection of mice with Plasmodium Berghei Anka (PbA) leads to a thrombocytopenia, due to a reduced platelet life span, eventually associated with a syndrome of severe or cerebral malaria (CM). Thrombocytopenia was associated with an increase in the number of microparticles (mcp) in plasma. More than >60% of these mcp were of platelet origin, as seen by staining with an anti-platelet antibody. The thrombocytopenia and the amount of mcp were decreased in mice treated with anti CD40L mAb, suggesting that CD40L is the main effector of the thrombocytopenia. Caspase-1, -3, -6, -8, -9 were activated in platelets from infected mice, as seen by the binding of labeled probes or the amount of pro-caspase-3. Treatment of infected mice with the caspases inhibitor ZVAD-fmk decreased the number of mcp and the thrombocytopenia, showing that platelet caspases are responsible for platelet fragmentation. In addition, the caspase inhibitor also caused a decrease in the mortality associated with CM, indicating a critical role of caspases in the expression of CM.