Sequestration of malaria-parasite-infected erythrocytes in the microvasculature of organs is thought to be a significant cause of pathology. Cerebral malaria (CM) is a major complication of Plasmodium falciparum infections, and PfEMP1-mediated sequestration of infected red blood cells has been considered to be the major feature leading to CM-related pathology. We report a system for the real-time in vivo imaging of sequestration using transgenic luciferase-expressing parasites of the rodent malaria parasite Plasmodium berghei. These studies revealed that: (i) as expected, lung tissue is a major site, but, unexpectedly, adipose tissue contributes significantly to sequestration, and (ii) the class II scavenger-receptor CD36 to which PfEMP1 can bind is also the major receptor for P. berghei sequestration, indicating a role for alternative parasite ligands, because orthologues of PfEMP1 are absent from rodent malaria parasites, and, importantly, (iii) cerebral complications still develop in the absence of CD36-mediated sequestration, dissociating parasite sequestration from CM-associated pathology. Realtime in vivo imaging of parasitic processes may be used to evaluate the molecular basis of pathology and develop strategies to prevent pathology.imaging ͉ Plasmodium ͉ P. berghei ͉ luciferase ͉ real-time in vivo imaging I nfected red blood cells (irbc) of many species of malaria parasites adhere to the endothelial cells of the microvasculature of numerous deep tissues (1, 2). Termed sequestration, this characteristic may facilitate parasite multiplication, avoiding removal of the irbc by the spleen (3, 4). In some parasite-host combinations, the process of sequestration is associated with pathogenesis, for example, Plasmodium falciparum in humans (1, 2, 5) and Plasmodium berghei in certain mouse strains (6, 7). Cerebral malaria (CM) is a major complication of P. falciparum infections, and the sequestration of irbc has been considered to be the major feature leading to CM-related pathology. Sequestration may lead to vascular obstruction, local endothelial cell activation, and the release of proinflammatory cytokines, resulting in damage to adjacent tissues (2, 7, 8). In P. falciparum, the class II scavenger receptor CD36 is a major endothelial receptor. CD36 is involved in not only the adherence of irbc (1, 9, 10) through specific domains of the surface variant antigen PfEMP-1 but also in the modulation of innate and adaptive immune responses (11,12). To date, most investigations of the dynamics of irbc-receptor interactions rely on in vitro observations with cultured cells and immobilized receptors (2). Despite the increase in knowledge of the molecules involved in the binding of irbc to endothelial cells, the specific interactions that lead to pathology have yet to be established. Infection with P. berghei in laboratory rodents is a well established model for the investigation of associations among CM, proinflammatory cytokines, and endothelial receptors involved in the sequestration of irbc, leukocytes, and platelet...

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CD36 is involved in high-affinity peripheral FFA uptake. CD36-deficient ( cd36 ؊ / ؊ ) mice exhibit increased plasma FFA and triglyceride (TG) levels. The aim of the present study was to elucidate the cause of the increased plasma TG levels in cd36 ؊ / ؊ mice. cd36 ؊ / ؊ mice showed no differences in hepatic VLDL-TG production or intestinal [ 3 H]TG uptake compared with wild-type littermates. cd36 ؊ / ؊ mice showed a 2-fold enhanced postprandial TG response upon an intragastric fat load ( P Ͻ 0.05), with a concomitant 2.5-fold increased FFA response ( P Ͻ 0.05), suggesting that the increased FFA in cd36 ؊ / ؊ mice may impair LPL-mediated TG hydrolysis. Postheparin LPL levels were not affected. However, the in vitro LPL-mediated TG hydrolysis rate as induced by postheparin plasma of cd36 ؊ / ؊ mice in the absence of excess FFA-free BSA was reduced 2-fold compared with wild-type plasma ( P Ͻ 0.05). This inhibition was relieved upon the addition of excess FFA-free BSA. Likewise, increasing plasma FFA in wild-type mice to the levels observed in cd36 ؊ / ؊ mice by infusion prolonged the plasma half-life of glycerol tri[ 3 H]oleate-labeled VLDL-like emulsion particles by 2.5-fold ( P Ͻ 0.05). We conclude that the increased plasma TG levels observed in cd36 ؊ / ؊ mice are caused by decreased LPL-mediated hydrolysis of TG-rich lipoproteins resulting from FFA-induced product inhibition of LPL. is abundant in peripheral tissues active in FFA metabolism, such as adipose tissue, skeletal muscle, and cardiac muscle, where it is involved in high-affinity uptake of FFA (1, 6, 7). To directly investigate a role for CD36 in lipid metabolism, mice lacking CD36 were generated by gene targeting (8). These CD36-deficient ( cd36 Ϫ / Ϫ ) mice exhibited increased plasma FFA and triglyceride (TG) levels (8). Coburn et al. (9) showed that FFA uptake was considerably impaired in muscle and adipose tissue of cd36 Ϫ / Ϫ mice. Febbraio et al. (8) further showed that the increase in plasma TG levels in the absence of CD36 was primarily attributable to an increase in VLDL-sized particles. Although these data suggest a role for CD36 in TG metabolism in addition to FFA metabolism, the exact mechanisms underlying the increased TG levels in cd36 Ϫ / Ϫ mice are unknown. It has been discussed by Hajri et al. (10) that the VLDL production rate may be enhanced in cd36 Ϫ / Ϫ mice, but the increased plasma TG levels may also be attributable to increased intestinal lipid absorption or to decreased LPL-mediated TG clearance from the circulation.Therefore, the aim of the present study was to elucidate the cause of the hypertriglyceridemia in cd36 Ϫ / Ϫ mice in vivo. Our results show that the increased plasma TG levels in cd36 Ϫ / Ϫ mice are caused by a decreased TG hydrolysis rate rather than by differences in the production of hepatic VLDL-TG or intestinal lipid absorption. From the present study, we conclude that the hypertriglyceridemia observed in cd36 Ϫ / Ϫ mice is caused by decreased LPLmediated hydrolysis of TG-rich lipoproteins resulting ...