Twenty-five years after its appearance, the HIV/AIDS epidemic represents more than ever a public health threat worldwide. About 35 million people are living with HIV/AIDS as of the end of 2007, most of them originating from emerging countries. Our work focuses on cellular and molecular aspects of HIV-1 replication, and on the mechanisms of recognition of HIV-infected cells by the immune system. Three close and complementary axes of research characterize our scientific activities.
The first axis is aimed at understanding the impact of HIV-1 infection on the biology of T cells. We study the impairment of intracellular trafficking and signaling pathways in infected lymphocytes, and the effects of the HIV-1 Nef protein on these processes. We have demonstrated that Nef manipulates endocytic and signaling pathways in primary T cells. Nef down-regulates the surface expression of CD4 and MHC-I. Nef also affects endocytosis and recycling of the TCR, and the localization of signaling kinases such as Lck. This results in an impaired formation of immunological synapses, when infected T cells encounter APCs. We now wish to understand more precisely what would be the advantages for the virus in manipulating the correct functioning of this synapse
MHC-I intracellular localization in non infected (right) and Nef-expressing lymphocytes
The second axis concerns the cellular and molecular mechanisms regulating HIV-1 replication. We are studying cell-to-cell viral spread. Direct cell-to-cell transfer represents a potent and rapid mode of viral propagation, which likely involves the formation of virological synapses between infected donor cells and uninfected recipients. We have recently underscored the role of ZAP-70, a kinase involved in T-cell activation and immunological synapse formation, in HIV replication. ZAP-70 facilitates cell-to-cell viral transfer and virological synapse formation. This indicates that HIV usurps components of the immunological synapse machinery to ensure its own spread through cell-to-cell contacts. We intend to document the links that may exist between cell activation and HIV spread.
HIV budding at the contact zone between one infected and one target cell
HIV cell-to-cell transfer (HIV in green, target cell in blue)
The aim of the third axis is a better knowledge of the interplay between viruses and the immune system of the host. We have focused our studies on APOBEC proteins, and deciphered a primary function of this family of cytidine deaminases, which is to inhibit retrotransposition of endogenous retroviruses. On the other hand, we have performed a long-standing analysis of the mechanisms of antigen presentation by dendritic cells (DCs) and of recognition of HIV-infected cells by antigen-specific CD4+ and CD8+ cytotoxic T lymphocytes (CTLs). We intend to further describe the mechanisms of HIV antigen presentation by DCs, and to unravel the links between antigen presentation and viral transfer.
Dendritic cell interacting with a lymphocyte
2. CHIKUNGUNYA VIRUS
An unprecedented epidemic of Chikungunya virus (CHIKV) infection recently occurred in countries of the Indian Ocean area, causing an acute and painful syndrome with strong fever, asthenia, skin rash, polyarthritis, and lethal cases of encephalitis. The basis for Chikungunya disease and the tropism of CHIKV remain unknown.
Our work is the result of a collaborative effort between numerous teams from Institut Pasteur, La Réunion hospital, and other institutions. Our aim was to establish a task force, with multiple and complementary expertise on virology, immunology and cell biology, in order to characterize this enigmatic virus.
We are studying the replication characteristics of recent clinical CHIKV strains. We recently showed that Human epithelial and endothelial cells, primary fibroblasts and, to a lower extent, monocyte-derived macrophages were sensitive to infection, and allowed viral production. In contrast, CHIKV did not replicate in lymphoid and monocytoid cell lines, primary lymphocytes and monocytes, nor in monocyte-derived dendritic cells. CHIKV replication was cytopathic and associated with an induction of apoptosis in infected cells. Chloroquine, bafilomycin-A1 and shRNAs against dynamin-2 inhibited viral production, indicating that viral entry occurs through pH-dependent endocytosis. CHIKV was highly sensitive to the antiviral activity of type I and II interferons. These results provide a general insight into the interaction between CHIKV and its mammalian host. We are currently describing further viral entry pathways in various cell types.
CHIKV-infected human macrophage (virus in red)
Chikungunya Virus (CHIKV) budding from an infected human cell