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CCR5-tropic (R5) immunodeficiency virus type 1 (HIV-1) strains are highly transmissible during the early stage of infection in humans, whereas CXCR4-tropic (X4) strains are less transmissible. This study aimed to explore the basis for early phase R5 and X4 HIV-1 infection in vivo by using humanized mice dually challenged with R5 HIV-1 NLAD8-D harboring DsRed and X4 HIV-1 NL-E harboring EGFP. Whereas R5 HIV-1 replicated well, X4 HIV-1 caused only transient viremia with variable kinetics; however, this was distinct from the low level but persistent viremia observed in mice challenged with X4 HIV-1 alone. Flow cytometric analysis of HIV-1-infected cells revealed that X4 HIV-1 infection of CCR5 + CD4 + T cells was significantly suppressed in the presence of R5 HIV-1. X4 HIV-1 was more cytopathic than R5 HIV-1; however, this was not the cause of restricted X4 HIV-1 infection because there were no significant differences in the mortality rates of CCR5 + and CCR5 − cells within the X4 HIV-1-infected cell populations. Taken together, these results suggest that restricted infection of CCR5 + CD4 + T cells by X4 HIV-1 (occurring via a still-to-be-identified mechanism) might contribute to the preferential transmission of R5 HIV-1 during the early phase of infection. [ABSTRACT FROM AUTHOR]

Abstract: Dendritic cells (DCs) are professional antigen-presenting cells that possess a unique capacity to cross-present exogenous antigens efficiently to CD8+ T cells. We previously demonstrated that monocyte-derived DCs (MDDCs) pulsed with yeast-derived HIV-1 Gag virus-like particles (VLPs) were able to activate Gag-specific CD8+ T cells from HIV-1-infected individuals. Yeast VLPs are abundantly mannosylated (high-mannose type: HmVLPs) and are highly immunogenic. Because lectin receptors are shown to negatively regulate Th1 responses, we investigated the relationship between VLP mannosylation level and MDDC cross-presentation activity. Poorly mannosylated VLPs (low-mannose type: LmVLPs) were prepared using a yeast mnn9 mutant strain that lacks a core mannosylation enzyme. We found that MDDCs pulsed with LmVLPs activated Gag-specific T cells more strongly than those pulsed with HmVLPs. However, MDDCs showed similar antigen uptake and intracellular transport of both types of VLPs. Interestingly, LmVLPs induced IL-12 production slightly more than HmVLPs (yet statistically significant). Furthermore, the level of LPS-induced IL-10 production was enhanced by pulsing with HmVLPs, but not with LmVLPs. These results indicate that lectin receptors recognizing mannose may influence the Th1/Th2 balance of the immune response, resulting in reduced efficiency of CD8+ T cell activation by a heavily mannosylated antigen presented by DCs. [Copyright &y& Elsevier]

Abstract: In response to SARS-CoV infection, neutralizing antibodies are generated against the Spike (S) protein. Determination of the active regions that allow viral escape from neutralization would enable the use of these antibodies for future passive immunotherapy. We immunized mice with UV-inactivated SARS-CoV to generate three anti-S monoclonal antibodies, and established several neutralization escape mutants with S protein. We identified several amino acid substitutions, including Y442F and V601G in the S1 domain and D757N and A834V in the S2 region. In the presence of each neutralizing antibody, double mutants with substitutions in both domains exhibited a greater growth advantage than those with only one substitution. Importantly, combining two monoclonal antibodies that target different epitopes effected almost complete suppression of wild type virus replication. Thus, for effective passive immunotherapy, it is important to use neutralizing antibodies that recognize both the S1 and S2 regions. [Copyright &y& Elsevier]

Abstract: Numerous studies indicated that Nef is a pleiotropic factor. Although it has been shown that Nef impairs the antigen-presenting activity of dendritic cells, more recent studies have shown no such impairment. This issue is critical for designing a vaccine expressing Nef. To refine our knowledge regarding the effect of Nef on dendritic cells, we developed constitutive and inducible adenovirus vector systems that express high levels of Nef in monocyte-derived dendritic cells (MDDCs). We showed here that Nef expression clearly downregulated CD4 expression of MDDCs but had little or no effect on other surface molecules, including MHC class I. Nef also did not affect the functional maturation of MDDCs. Use of the inducible Nef-expression system clearly revealed that adenovirus infection per se modulates cytokine secretion and the expression of apoptosis-related molecules in MDDCs, whereas Nef had no effect on these functions. Moreover, the antigen-presenting activity of MDDCs was not disturbed by the presence of Nef. On the contrary, we found that Nef-expressing MDDCs generated from HIV-1-infected individuals efficiently activated Nef-reactive T cells. Therefore, although adenovirus vector may modulate some aspects of MDDC function, Nef-expressing adenovirus would be served as one of HIV vaccine candidates. [Copyright &y& Elsevier]

Several mechanisms underline induction of CD4 T-cell death by human immunodeficiency virus (HIV) infection. For a long time, apoptosis was considered central to cell death involved in the depletion of CD4 T cells during HIV infection. However, which types of cell death are induced during the early phase of HIV infection in vivo remains unclear. In this study, CD4 T-cell death induced in early HIV infection was characterized using humanized mice challenged with CCR5-tropic (R5) or CXCR4-tropic (X4) HIV-1. Results showed that CD4 T-cell death was induced in the spleen 3 days post-challenge with both R5 and X4 HIV-1. Although cell death without caspase-1 and caspase-3/7 activation was preferentially observed, caspase-1+ pyroptosis was also significantly induced within the memory subpopulation by R5 or X4 HIV-1 and the naïve subpopulation by X4 HIV-1. In contrast, caspase-3/7+ apoptosis was not enhanced by either R5 or X4 HIV-1. Furthermore, phosphorylated mixed lineage kinase domain-like protein+ necroptosis was induced by only X4 HIV-1. These findings indicate that various types of non-apoptotic CD4 T-cell death, such as pyroptosis and necroptosis, are induced during the early phase of HIV infection in vivo. [ABSTRACT FROM AUTHOR]