Marina Viora

HIV-1 Nef triggers Vav-mediated signaling pathway leading to functional and morphological differentiation of dendritic cells.

The accessory HIV‐1 Nef protein plays a key role in AIDS pathogenesis. We recently demonstrated that exogenous Nef triggers phenotypic and functional differentiation of immature dendritic cells (DCs). Here we investigated whether the Nef‐induced DC differentiation occurs with morphological remodeling and have focused on the interference of Nef in the signaling pathways that regulates DC maturation. We found that exogenous Nef enters immature DCs, promoting their functional and morphological differentiation. Specifically, Nef promotes interleukin (IL) ‐12 release, which closely fits with nuclear factor (NF) ‐κB activation. Nef induces rearrangement of actin microfilaments, leading to uropod and ruffle formation. Moreover, Nef increases the capacity of DCs to form clusters with allogeneic CD4+ T cells, improving immunological synapse formation. Searching for molecules involved in Nef‐triggered signaling pathways driving the DC maturation, we found that Nef targets Vav and promotes its tyrosine phosphorylation, associated with its nucleus‐to‐cytoplasm redistribution. This has a direct effect on Vav guanine nucleotide exchange factor activity for the small GTPase Rac1. We hypothesize that targeting Vav, Nef modulates both early signaling events (such as cytoskeletal rearrangement) and delayed responses (such as transcriptional regulation), promoting DC differentiation. Our results highlight how Nef may enhance T lymphocyte activation, thus fostering virus dissemination, manipulating the DC arm of the immune response.—Quaranta, M. G., Mattioli, B., Spadaro, F., Straface, E., Giordani, L., Ramoni, C., Malorni, W., Viora, M. HIV‐1 Nef triggers Vav‐mediated signaling pathway leading to functional and morphological differentiation of dendritic cells. FASEB J. 17, 2025–2036 (2003)

HIV-1 Nef equips dendritic cells to reduce survival and function of CD8+ T cells: a mechanism of immune evasion

The accessory HIV‐1 Nef protein is a crucial determinant for viral replication and pathogenesis. During HIV infection, loss of immune control in the setting of a strong and broad HIV‐specific T‐lymphocyte response, leads to a lethal outcome through AIDS. Moreover, dysfunction of dendritic cells (DCs) may contribute to the immune suppression associated with AIDS progression. We recently demonstrated that exogenous Nef selectively activates immature DCs manipulating their phenotypical, morphological, and functional developmental program. Here, we tracked whether Nef, targeting DCs, could be involved in the dysregulation of CD8+ T cell responses. We found that Nef inhibits the capacity of DCs to prime alloreactive CD8+ T cell responses down‐regulating their proliferation and functional competence. This coincides with the induction of CD8+ T cell apoptosis. Nef oversees apoptotic killing of CD8+ T cells up‐regulating TNF‐α and FasL production by DCs and interfering with the death receptor pathway in CD8+ T cells and thus activating caspase 8. Our findings suggest that Nef may contribute to the immune evasion associated with HIV‐1 infection, subverting DC biology. This may help explain the pleiotropic function that Nef plays during infection and makes this protein an attractive target for preventive and therapeutic intervention.

Redox imbalance and immune functions: opposite effects of oxidized low‐density lipoproteins and N‐acetylcysteine

This study investigates the in vitro effects of oxidized low‐density lipoproteins (ox‐LDL), ‘physiological’ pro‐oxidants, N‐acetylcysteine (NAC), a free radical scavenger and glutathione precursor, and their combination on human peripheral blood mononuclear cell functions. We found that treatment with ox‐LDL induced a significant down‐regulation of proliferative response to mitogens, antigens and interleukin‐2. Lipid extracts from ox‐LDL were able to reproduce the same effect as the lipoprotein. On the other hand, NAC exposure induced a significant up‐regulation of proliferative responses to all the stimuli used. Moreover, we showed that natural killer (NK) cell‐mediated cytotoxic activity was significantly down‐regulated by ox‐LDL while treatment with NAC induced a significant up‐regulation of NK‐cell activity. Finally, we found that ox‐LDL and NAC exerted opposite effects on the cytokine network, interfering both at the protein secretion level and the messenger RNA synthesis level. More importantly, when NAC was used in combination with ox‐LDL the proliferative responses, NK‐cell‐mediated cytotoxic activity and cytokine production were restored to values comparable to controls. These data indicate that ox‐LDL and NAC modulate immune functions, exerting opposite effects reflecting their pro‐oxidant and antioxidant behaviours. Our results add new insights to the key role played by redox imbalance as a modulator of immune system homeostasis and suggest that an antioxidant drug such as NAC could be useful against pathologies associated with an increase in lipid peroxidation.

HIV-1 Nef impairs the dynamic of DC/NK crosstalk: different outcome of CD56dim and CD56bright NK cell subsets

Dendritic cells (DCs) and natural killer (NK) cells are essential components of the innate immunity and play a critical role in the first phase of host defense against infection. Interactions between DCs and NK cells have been demonstrated in a variety of settings, with evidence emerging of complex bidirectional crosstalk between the two cell types. The accessory HIV‐1 Nef protein is a crucial determinant for viral replication and pathogenesis. We previously demon‐strated that Nef, hijacking DC functional activity, subverts the DC arm of immune response to escape the adaptive immune attack. Here, we monitor the effect of Nef on the outcome of the innate immune response, focusing on the impact of Nef on DC/NK crosstalk. We demonstrate that Nef up‐regulates the ability of DCs to stimulate the immunoregulatory NK cells (CD56bright) as assessed by the activated phenotype, up‐regulation of their proliferative response and INF‐γ release. On the other hand, Nef‐pulsed DCs inhibit cytotoxic NK cells (CD56dim), as assessed by the reduced HLA‐DR surface expression, reduced proliferation and cytotoxic activity. Moreover, in the presence of Nef‐pulsed DCs, we found a significant up‐regulation of TNF‐α secretion and a significant reduction of IL‐10, GM‐CSF, MIP‐1α and RANTES secretion. Our findings suggest that the Nef‐induced dysregulation in the DC/NK cell crosstalk may represent a potential mechanism through which HIV escapes innate immune surveillance.—Quaranta, M.G., Napolitano, A., Sanchez, M., Giordani, L., Mattioli, B., Viora, M. HIV‐1 Nef impairs the dynamic of DC/NK crosstalk: different outcome of CD56dim and CD56bright NK cell subsets. FASEB J. 21, 2323–2334 (2007)

The influence of sex and gender on immunity, infection and vaccination

Sex/gender significantly contribute to shape the immune responses, contributing to differences in the pathogenesis of infectious diseases in males and females, the response to viral vaccines and the prevalence of autoimmune diseases. Females typically develop higher innate, humoral and cellular immune responses to viral infections and in response to vaccine. At the same time, women are more prone to autoimmune diseases and experience more adverse reactions to vaccination. Hormonal, genetic and environmental factors between males and females may affect the immune responses and the sex-related outcome of vaccination. Knowledge of the mechanisms involved in sex disparity in immune responses will contribute to identify the ways to reduce adverse reactions in females and to improve the immune responses in males. This is necessary to adequately protect both sexes against the immune-mediated and infectious diseases with the long-term goal of personalizing the therapies for males and females.