Dengue specific T cell responses evaluated by ELISPOT assay. BALB/c mice were immunized with DENV1-4 VLPs or virions in either monovalent A) or tetravalent B) formula. The immunized mice were sacrificed at day 42 and the collected spleen cells were isolated and stimulated in vitro with each of DENV1-4 VLPs. ELISPOT assay was performed to test IFN-γ production. The mean number of spot forming cells (SFCs)/106 splenocytes was shown as VLPs-stimulated plus mock-stimulated with an S.D bar. *indicates statistical significance (P < 0.05).