At day 4 or 5 5 post-DENV4 infection, plaque assays were performed on tissue from the lymph nodes and bone marrow cells. familyFlaviviridae, are the causative brokers of the mosquito-borne illness dengue fever (DF), which affects over 50 million people annually. In some cases, DF progresses to dengue hemorrhagic fever/dengue shock syndrome (DHF/DSS), which is a severe, life-threatening disease characterized by increased vascular permeability responsible for 250,000-500,000 hospitalizations each year in tropical and sub-tropical regions worldwide (Gubler, 1998). Although a number of dengue vaccine candidates are in various stages of clinical trials, no specific therapies or vaccines are currently available (Hombach, 2007;Whitehead et al., 2007). A successful tetravalent dengue vaccine must confer robust protection against all four serotypes of DENV, as previous contamination by one serotype is usually a recognized risk factor for DHF/DSS following a heterologous (cross-serotype-reactive) DENV contamination (Halstead, 1981). Nonetheless, most primary and secondary DENV infections are asymptomatic (Balmaseda et al., 2006;Burke et al., 1988;Endy et al., 2002), and CB-6644 the mechanistic basis of protection versus enhancement in sequential DENV infections is not well-defined. Epidemiologic studies in humans yield invaluable information; however, animal models of DENV contamination allow characterization of protective as well as pathologic immune responses during a secondary DENV contamination in vivo. Studies of heterologous DENV infections have been conducted in non-human primates and to a limited Mouse monoclonal to Epha10 extent in mice. In monkeys, sequential heterologous DENV infections resulted in either protection (Kochel et al., 2005), partial protection (Koraka et al., 2007;Scherer et al., 1972) or enhancement (Marchette et al., 1973). Enhanced contamination after transfer of either pooled human cord blood from DENV-immune mothers (Halstead, 1979) or a chimeric human-chimpanzee anti-DENV neutralizing monoclonal antibody (mAb) (Goncalvez et al., 2007) resulted in increased viremia in rhesus monkeys that is postulated to represent antibody-dependent CB-6644 enhancement (ADE). In mice, protection from death using a secondary, homologous (serotype-specific) DENV contamination has been exhibited (Johnson and Roehrig, 1999;Price and Thind, 1972); while reports of heterologous sequential DENV infections in mice noted an increase in thrombocytopenia (Sarkar et al., 1976) or documented heterologous immune responses (Beaumier et al., 2008). To the best of our knowledge, no published study in mice has documented the occurrence of either protection or enhancement of DENV titers in sequential, heterologous infections. Wildtype mice are susceptible to DENV infection only after high doses and do not manifest robust viral replication (Chen et al., CB-6644 2004;Huang et al., 2000;Paes et al., 2005;Shresta et al., 2004a). Thus, various immunocompromised mice have been used to test responses to DENV in vivo (An et al., 1999;An et al., 2004;Bente et al., 2005;Blaney et al., 2002;Johnson and Roehrig, 1999;Lin et al., 1998;Shresta et al., 2004b;Wu et al., 1995). In this study, mice of the 129 CB-6644 strain lacking receptors for interferon (IFN)-/ and IFN- (AG129) were used to model sequential DENV infections. AG129 mice have a number of relevant attributes; for instance, they support robust replication of clinical isolates of all four DENV serotypes ((Kyle et al., 2007;Shresta et al., 2004b), S. Balsitis and E. Harris, unpublished data), display cellular tropism similar to that seen in humans (Durbin et al., 2008;Kyle et al., 2007;Neves-Souza et al., 2005), exhibit thrombocytopenia that is inversely related to viral load (S. Balsitis and E. Harris, unpublished data), develop high levels of soluble non-structural 1 (NS1) CB-6644 protein during DENV infection comparable to levels seen in humans (Schul et al., 2007; S. Balsitis and E. Harris, unpublished data), and experience increased vascular permeability upon infection with certain DENV strains (Shresta et al., 2006). In addition, AG129.