The role of CD8 + T cells in dengue virus infection and subsequent disease manifestations is not fully understood. According to the original antigenic sin theory, skewing of T-cell responses induced by primary infection with one serotype causes less effective response upon secondary infection with a different serotype, predisposing individuals to severe disease. A comprehensive analysis of CD8 + responses in the general population from the Sri Lankan hyperendemic area, involving the measurement of ex vivo IFNγ responses associated with more than 400 epitopes, challenges the original antigenic sin theory. Although skewing of responses toward primary infecting viruses was detected, this was not associated with impairment of responses either qualitatively or quantitatively. Furthermore, we demonstrate higher magnitude and more polyfunctional responses for HLA alleles associated with decreased susceptibility to severe disease, suggesting that a vigorous response by multifunctional CD8 + T cells is associated with protection from dengue virus disease.

T-cells have to recognize peptides presented on MHC molecules to be activated and elicit their effector functions. Several studies demonstrate that some peptides are more immunogenic than others and therefore more likely to be T-cell epitopes. We set out to determine which properties cause such differences in immunogenicity. To this end, we collected and analyzed a large set of data describing the immunogenicity of peptides presented on various MHC-I molecules. Two main conclusions could be drawn from this analysis: First, in line with previous observations, we showed that positions P4–6 of a presented peptide are more important for immunogenicity. Second, some amino acids, especially those with large and aromatic side chains, are associated with immunogenicity. This information was combined into a simple model that was used to demonstrate that immunogenicity is, to a certain extent, predictable. This model (made available at http://tools.iedb.org/immunogenicity/) was validated with data from two independent epitope discovery studies. Interestingly, with this model we could show that T-cells are equipped to better recognize viral than human (self) peptides. After the past successful elucidation of different steps in the MHC-I presentation pathway, the identification of variables that influence immunogenicity will be an important next step in the investigation of T-cell epitopes and our understanding of cellular immune responses.

Dengue virus (DENV) is a rapidly spreading pathogen with unusual pathogenesis, and correlates of protection from severe dengue disease and vaccine efficacy have not yet been established. Although DENV-specific CD8 + T-cell responses have been extensively studied, the breadth and specificity of CD4 + T-cell responses remains to be defined. Here we define HLA-restricted CD4 + T-cell epitopes resulting from natural infection with dengue virus in a hyperepidemic setting. Ex vivo flow-cytometric analysis of DENVspecific CD4+ T cells revealed that the virus-specific cells were highly polarized, with a strong bias toward a CX3CR1 A ll four of the dengue virus serotypes (DENV 1-4) have spread rapidly within countries and across regions in the past few decades, resulting in an increased frequency of epidemics and severe dengue disease. Multiple serotypes circulate simultaneously in many tropical countries, and recent outbreaks have been reported in Europe and the continental United States (1, 2). These circumstances make dengue the most prevalent and rapidly spreading mosquito-borne viral disease in humans (3). Recent reports estimate that 390 million infections occur each year, with ∼25% of cases resulting in symptomatic disease (2).All four dengue serotypes can cause a spectrum of disease, ranging from self-limiting dengue fever to potentially lethal severe dengue disease, such as states of dengue hemorrhagic fever and Dengue shock syndrome, which are associated with the plasma leakage syndromes leading to visceral organ injury (4). It is not yet fully understood why only a subset of people infected with DENV progresses to severe disease. One risk factor for severe disease is the acquisition of DENV-reactive Abs before secondary infection with a different serotype (heterologous infection). These Abs can either be acquired from a previous infection with a different serotype or, in the case of infants, acquired from an immune mother (5, 6). It has been shown that subneutralizing levels of DENV-specific Abs exacerbate disease in a phenomenon termed Ab-dependent enhancement of infection (7,8). In brief, dengue-specific crossreactive Abs produced after an initial DENV infection combine with those produced after a second viral infection to form immune complexes that perpetuate infection by increasing the number of infected cells and, therefore, viral output per cell (6).The observation that only a minority of patients develops severe disease suggests that host genetic factors may play an important role in disease severity. Relatedly, a role for T cells in control of disease has been suggested by several studies that correlate the expression of certain HLA molecules with susceptibility to or protection from DENV disease (9-15). HLA molecules are one of the most polymorphic host factors in humans, with several thousand variants thus far known (16,17). Each HLA variant is present with variable frequency, depending on ethnic lineage and geographic locality. For HLA class I MHC restricted responses, it has been recently shown tha...