Fig. 1.

A mouse model of DENV secondary infection. (a) C57BL/6 mice were infected i.p. with DENV-1, cell supernatant (placebo) or DENV-2 and 60 days later, challeged i.p. with DENV-2. (b–f) Hematological and biochemical parameters at 7 days post-secondary infection in mice infected sequentially with DENV-1/DENV-2, placebo/DENV-2, and DENV-2/DENV-2. (g) Histopathology showing hematopoietic centers in liver (arrow) and megakaryocytes in spleen (arrow) of mice infected with DENV-1/DENV-2 compared to mice infected with placebo/DENV-2, and those receiving two doses of DENV-2. Magnification: 400 ×. H&E staining. (h, i) Scores for megakaryocytes and bleeding time. (j) Mice immune against DENV-1 or DENV-2 and later infected with DENV-2 received Evans Blue 7 days post-secondary infection, and 2 h later the dye was extracted from tissues with formamide and absorbance was measured at 610 nm. ALT: alanine aminotransferase; AST: aspartate aminotransferase; CK: creatine kinase; LDH: lactate dehydrogenase. Values represent means ± SEM (n = 4–6/group). Two independent experiments were performed that showed similar results. Statistical significance between groups using one-way ANOVA is depicted with a dashed line at the top of the graph, and Bonferroni's multiple comparison post-test is indicated with solid lines connecting two bars (*p < 0.05, **p < 0.01, ***p < 0.001).