We generated two transgenicP. tissue sequestration. In humans the spleen plays a crucial role in defense against infections with viruses, bacteria, fungi, and parasites. Important functions of the spleen include removal of old and abnormal blood cells, removal of circulating pathogens, and facilitating development of immune responses against these pathogens (Mebius and Kraal, 2005). Malaria is an infectious disease caused byPlasmodiumparasites and it is intimately associated with forms of the parasite that invade and multiply within red blood cells (rbc). It has been shown that the spleen plays an active role in the retention and removal of malaria-infected rbc (irbc) from the blood circulation (Engwerda et al., 2005;Buffet et al., 2011) and has a central role in the development of immune responses directed against the parasites (Langhorne et al., 2004;Engwerda et al., 2005). Recognition of irbc by the spleen may result from alterations in erythrocyte membrane rigidity induced by changes in the composition and/or distribution of erythrocyte proteins/molecules or through the exposure ofPlasmodium-specific proteins on or at the irbc surface membrane (Maier et al., 2009;Buffet et al., 2011). The human malaria parasitePlasmodium falciparumactively remodels the host erythrocyte through exporting parasite proteins into the host cytoplasm and to the irbc surface (Maier et al., 2009;Goldberg and Cowman, 2010). This remodeling can lead to alterations in irbc deformability and changes in surface membrane protein composition (Dondorp et al., 2000;Maier et al., 2009). One of the best characterizedP. falciparumproteins exposed on the irbc surface is PfEMP1, a variant antigen encoded by Rabbit polyclonal to DYKDDDDK Tag the family of so-calledvargenes (Scherf et al., 2008;Maier et al., 2009). This protein mediates adhesion to several receptors present on endothelial cells of the microvasculature, such as CD36 and ICAM1 (Sherman et al., 2003;Chakravorty and Craig, 2005;Rowe et al., 2009) and to chondroitin sulfate (CSA) that is present on the surface of syncytiotrophoblasts of the placenta (Fried and Duffy, 1996;Srivastava et al., 2010). PfEMP1-mediated adherence results in tissue sequestration of irbc, removing them from the peripheral blood circulation. The Avosentan (SPP301) prevailing hypothesis for why irbc sequestration occurs is that it prevents spleen-mediated clearance of irbc and thus benefits the parasite survival and maintenance of an infection (Sherman et al., 2003;Buffet et al., 2011). Sequestration of irbc in the microvasculature of organs such as the lungs, brain, and placenta is thought to directly contribute to severe pathologies associated withP. falciparuminfections, such as cerebral malaria and pregnancy-associated malaria (Rogerson et al., 2007;Mishra and Newton, 2009). It has been shown that sequestration of irbc can lead to vascular obstruction, metabolic disturbances such as acidosis and Avosentan (SPP301) local endothelial cell activation, and release of proinflammatory cytokines (Miller et al., 2002;Schofield and Grau, 2005;Mishra and Newton, 2009). Because of the central role of irbc sequestration in malaria pathogenesis, strategies are being pursued to develop anti-adhesion adjunctive therapies for reducing sequestration and thereby reducing severe disease and mortality (Rowe et al., 2009;Avril et al., 2010;John et al., 2010). Such anti-adhesion therapies may reduce pathology directly by reducing parasite loads in critical tissues or may also result in decreased rate of parasite expansion (e.g., growth rate) as a result of the removal of nonsequestering irbc by the spleen. However, how sequestration affects parasite growth and avoidance of spleen-mediated clearance has not been experimentally validated and remains largely unknown. In this study, we have used a rodent model of malaria,Plasmodium berghei ANKA, to experimentally assess in vivo the importance of tissue sequestration on parasite growth rate and spleen-mediated removal of irbc.P. berghei ANKAsequesters in a fashion analogous toP. falciparumin that irbc containing the maturing forms (schizonts) are not present in the peripheral blood but are sequestered Avosentan (SPP301) in organs such as the lungs and adipose tissue (Franke-Fayard et al., 2005,2010;Spaccapelo et al., 2010). Moreover,P. berghei ANKAirbc adhere to the class II scavenger receptor CD36 (Franke-Fayard et al., 2005), which is also one of the major human receptors to whichP. falciparumirbc adhere. In contrast toP. falciparum, where PfEMP1 has been identified as the critical parasite ligand that binds to CD36, aP. berghei ANKAprotein responsible for CD36-mediated adherence remains to be identified because theP. berghei ANKAgenome does not contain any direct orthologues of the PfEMP1-encodingvargenes (Hall et al., 2005). This is despite human and mouse CD36 showing high sequence and structural similarity Avosentan (SPP301) (Silverstein and Febbraio, 2009). In our study, we have used a proteomic analysis ofP. berghei ANKAirbc membranes to identify parasite.