BACKGROUND: Dengue virus (DENV) serotype -2 and -3 infections are associated with more severe disease outcomes than -1 and -4, though a biological explanation for this has not been identified.

METHODS: DENV serotype effects on human T cell activation were assessed by measuring T cell receptor (TCR)-mediated IL-2 release following TCR stimulation. DENV envelope (env) proteins were expressed in Jurkat CD4+ T cell lines and regions inhibiting TCR inhibition mapped by mutagenesis. TCR-signaling pathway inhibition was characterized by total internal reflection fluorescence microscopy and immunoblot. Reverse genetics validated env mapping results.

RESULTS: T cell incubation with DENV-1 and -4 inhibited TCR signaling whereas DENV-2 and -3 did not. Inhibition did not require viral replication. DENV env protein expression inhibited TCR by interfering with activation of proximal TCR signaling events. Amino acids (aa's) 49 to 62 of DENV 1 env were sufficient to inhibit TCR signaling, with env aa's 55 and 66 being critical. Reverse genetics confirmed that substitution of DENV-2 and -3 aa's 55 and 66 into DENV-1 and -4 reversed TCR inhibition, and DENV-1 aa 55 and 66 introduced into DENV-2 and -3 enhanced TCR inhibition.

CONCLUSIONS: DENV-2 and -3 are associated with more severe clinical disease than DENV-1 and -4; however, no biological explanation for this difference has been previously identified. We found that DENV-1 and -4 viral particles and env proteins blunt T cell responses by interfering with proximal TCR signaling while DENV-2 and -3 do not, potentially explaining DENV pathogenic outcomes in primary and secondary infection.