T-Cell Memory Responses Elicited by Yellow Fever Vaccine are Targeted to Overlapping Epitopes Containing Multiple HLA-I and -II Binding Motifs

The yellow fever vaccines (YF-17D-204 and 17DD) are considered to be among the safest vaccines and the presence of neutralizing antibodies is correlated with protection, although other immune effector mechanisms are known to be involved. T-cell responses are known to play an important role modulating antibody production and the killing of infected cells. However, little is known about the repertoire of T-cell responses elicited by the YF-17DD vaccine in humans. In this report, a library of 653 partially overlapping 15-mer peptides covering the envelope (Env) and nonstructural (NS) proteins 1 to 5 of the vaccine was utilized to perform a comprehensive analysis of the virus-specific CD4+ and CD8+ T-cell responses. The T-cell responses were screened ex-vivo by IFN-γ ELISPOT assays using blood samples from 220 YF-17DD vaccinees collected two months to four years after immunization. Each peptide was tested in 75 to 208 separate individuals of the cohort. The screening identified sixteen immunodominant antigens that elicited activation of circulating memory T-cells in 10% to 33% of the individuals. Biochemical in-vitro binding assays and immunogenetic and immunogenicity studies indicated that each of the sixteen immunogenic 15-mer peptides contained two or more partially overlapping epitopes that could bind with high affinity to molecules of different HLAs. The prevalence of the immunogenicity of a peptide in the cohort was correlated with the diversity of HLA-II alleles that they could bind. These findings suggest that overlapping of HLA binding motifs within a peptide enhances its T-cell immunogenicity and the prevalence of the response in the population. In summary, the results suggests that in addition to factors of the innate immunity, "promiscuous" T-cell antigens might contribute to the high efficacy of the yellow fever vaccines. © 2013 de Melo et al

Babassu aqueous extract (BAE) as an adjuvant for T helper (Th)1-dependent immune responses in mice of a Th2 immune response-prone strain

<p>Abstract</p> <p>Background</p> <p>The aqueous extract of a Brazilian palm-tree fruit - the babassu - (BAE) exerts a clear immunostimulative activity <it>in vivo</it>. In the present work, the possibility that BAE can promote Th1 immune responses in mice of a Th2 immune response-prone strain - the BALB/c was investigated. BAE itself, and preparations consisting of <it>Leishmania amazonensis </it>promastigote extract (LE), adsorbed or not to Al(OH)₃, and in the presence or not of BAE, were used as immunogens. LE and Al(OH)₃have been shown to preferentially elicit Th2 immune responses.</p> <p>Results</p> <p>The addition of BAE to LE-containing immunogenic preparations, adsorbed or not to Al(OH)₃, clearly promoted the <it>in vitro </it>production of interferon γ (IFN-γ), a major Th1-dependent cytokine, and not of interleukin (IL-)4 (a Th2-dependent cytokine), by LE-stimulated splenocytes of immunized BALB/c mice. It also promoted the <it>in vivo </it>formation of IgG2a anti-LE antibodies. However, immunization with LE by itself led to an increased production of IL-4 by LE-stimulated splenocytes, and this production, albeit not enhanced, was not reduced by the addition of BAE to the immunogen. On the other hand, the IL-4 production by LE-stimulated splenocytes was significantly lower in mice immunized with a preparation containing Al(OH)₃-adsorbed LE and BAE than in mice immunized with the control preparation of Al(OH)₃-adsorbed LE without BAE. Moreover, an increased production of IFN-γ, and not of IL-4, was observed in the culture supernatants of splenocytes, from BAE-immunized mice, which were <it>in vitro </it>stimulated with BAE or which received no specific <it>in vitro </it>stimulus. No differences in IL-10 (an immunoregulatory cytokine) levels in the supernatants of splenocytes from mice that were injected with BAE, in relation to splenocytes from control mice, were observed. The spontaneous <it>ex vivo </it>production of NO by splenocytes of mice that had been injected with BAE was significantly higher than the production of NO by splenocytes of control mice.</p> <p>Conclusions</p> <p>Based on the results described above, BAE, or biologically active molecules purified from it, should be further investigated as a possible adjuvant, in association or not with aluminium compounds, for the preferential induction of Th1-dependent immune responses against different antigens in distinct murine strains and animal species.</p

Dengue-2 Structural Proteins Associate with Human Proteins to Produce a Coagulation and Innate Immune Response Biased Interactome

<p>Abstract</p> <p>Background</p> <p>Dengue virus infection is a public health threat to hundreds of millions of individuals in the tropical regions of the globe. Although Dengue infection usually manifests itself in its mildest, though often debilitating clinical form, dengue fever, life-threatening complications commonly arise in the form of hemorrhagic shock and encephalitis. The etiological basis for the virus-induced pathology in general, and the different clinical manifestations in particular, are not well understood. We reasoned that a detailed knowledge of the global biological processes affected by virus entry into a cell might help shed new light on this long-standing problem.</p> <p>Methods</p> <p>A bacterial two-hybrid screen using DENV2 structural proteins as bait was performed, and the results were used to feed a manually curated, global dengue-human protein interaction network. Gene ontology and pathway enrichment, along with network topology and microarray meta-analysis, were used to generate hypothesis regarding dengue disease biology.</p> <p>Results</p> <p>Combining bioinformatic tools with two-hybrid technology, we screened human cDNA libraries to catalogue proteins physically interacting with the DENV2 virus structural proteins, Env, cap and PrM. We identified 31 interacting human proteins representing distinct biological processes that are closely related to the major clinical diagnostic feature of dengue infection: haemostatic imbalance. In addition, we found dengue-binding human proteins involved with additional key aspects, previously described as fundamental for virus entry into cells and the innate immune response to infection. Construction of a DENV2-human global protein interaction network revealed interesting biological properties suggested by simple network topology analysis.</p> <p>Conclusions</p> <p>Our experimental strategy revealed that dengue structural proteins interact with human protein targets involved in the maintenance of blood coagulation and innate anti-viral response processes, and predicts that the interaction of dengue proteins with a proposed human protein interaction network produces a modified biological outcome that may be behind the hallmark pathologies of dengue infection.</p