Métabolisme cellulaire et régulation des réponses immunes [Cellular metabolism and regulation of immune responses]
To gain insight into the genetic basis of inflammation, our laboratory has recently undertaken the identification of genes selectively expressed by DCs, a cell population known to play a major role in the control of inflammatory responses. Using a modified differential display strategy, we have identified a series of transcripts representing genes specifically upregulated in DCs. One of the transcripts has been found to represent the murine homolog of a bacterial gene coding for a nicotinamide phosphoribosyl transferase (NAmPRTase), an enzyme involved in NAD biosynthesis. We have recently demonstrated that similarly to its microbial counterpart, the murine protein is a NAmPRTase, catalyzing the condensation of nicotinamide with 5-phosphoribosyl-1-pyrophosphate to yield nicotinamide mononucleotide, an intermediate in the biosynthesis of Nicotinamide adenine dinucleotide (NAD). This observation led us to further explore the possible relationship between NAD metabolism and the control of immune responses. Nicotinamide adenine dinucleotide (NAD) has been known for several decades to play a major role as a coenzyme in numerous oxidation-reduction reactions. Recently, the distinct role of NAD as a precursor for molecules involved in regulatory processes has also been recognized. NAD can indeed serve as a substrate for covalent protein modification catalysed by enzymes identified as ADP-ribosyl transferases. During ADP ribosylation, the ADP-ribose moiety of NAD is enzymatically transferred onto an acceptor protein, a reaction known to profoundly affect the target protein effector function. Numerous proteins endowed with ADP-ribosyl tyransferase capacity have been identified in mammals including mono and poly (ADP-ribosyl) transferases (respectively mARTs and PARPs) and sirtuins. This novel class of NAD-dependent protein deacetylases is involved in gene and has recently attracted great interest following the demonstration that they may play a role in cell longevity in both yeast and C. elegans. Elevated expression of the NAmPRTase in cells of the innate immune system has led us to postulate an important role for NAD-dependent enzymes in the control of the inflammatory response, an hypothesis presently under investigation in our laboratory. [To gain insight into the genetic basis of inflammation, our laboratory has recently undertaken the identification of genes selectively expressed by DCs, a cell population known to play a major role in the control of inflammatory responses. Using a modified differential display strategy, we have identified a series of transcripts representing genes specifically upregulated in DCs. One of the transcripts has been found to represent the murine homolog of a bacterial gene coding for a nicotinamide phosphoribosyl transferase (NAmPRTase), an enzyme involved in NAD biosynthesis. We have recently demonstrated that similarly to its microbial counterpart, the murine protein is a NAmPRTase, catalyzing the condensation of nicotinamide with 5-phosphoribosyl-1-pyrophosphate to yield nicotinamide mononucleotide, an intermediate in the biosynthesis of Nicotinamide adenine dinucleotide (NAD). This observation led us to further explore the possible relationship between NAD metabolism and the control of immune responses. Nicotinamide adenine dinucleotide (NAD) has been known for several decades to play a major role as a coenzyme in numerous oxidation-reduction reactions. Recently, the distinct role of NAD as a precursor for molecules involved in regulatory processes has also been recognized. NAD can indeed serve as a substrate for covalent protein modification catalysed by enzymes identified as ADP-ribosyl transferases. During ADP ribosylation, the ADP-ribose moiety of NAD is enzymatically transferred onto an acceptor protein, a reaction known to profoundly affect the target protein effector function. Numerous proteins endowed with ADP-ribosyl tyransferase capacity have been identified in mammals including mono and poly (ADP-ribosyl) transferases (respectively mARTs and PARPs) and sirtuins. This novel class of NAD-dependent protein deacetylases is involved in gene and has recently attracted great interest following the demonstration that they may play a role in cell longevity in both yeast and C. elegans. Elevated expression of the NAmPRTase in cells of the innate immune system has led us to postulate an important role for NAD-dependent enzymes in the control of the inflammatory response, an hypothesis presently under investigation in our laboratory.]

Développement et fonction des cellules ''T helper'' dans la production d'anticorps in vivo [Development and function of helper T cells for antibody production in vivo]
CD4+ T lymphocytes play a central role in antibody responses to T cell dependent antigens by activating B lymphocytes, promoting their survival and allowing affinity maturation and isotype switch. CD4+ T cells also control cell-mediated immune responses as well as allergic reactions. It is still unclear whether CD4+ T lymphocytes helping B cells represent a specialised sub-population or if they belong to a larger population having multiple functions. Recent data from the literature and vaccination studies suggest that CD4+ T cell-dependent antibody secretion by B lymphocytes could be dissociated from production of Th1 and Th2 cytokines. The aim of our project is to identify and characterize CD4+ T lymphocytes specialised in helping antibody production by B lymphocytes. As T helper cell for antibody secretion cannot be distinguished from naive T cells on a cytokine production-base data, we developed an in vitro test to directly detect their capacity to sustain an IgG class switch in B cell cooperation tests. This experimental setting allowed us to compare the B cell help activity mediated by distinct CD4+ T cell populations obtained following antigen inoculation in transgenic mice. Our results suggest that B helper T cells differ from both Th1 and Th2 cells and could therefore represent a 'new' CD4+ T cell population (ThB) distinct from the 'classical' Th1 and Th2 cytokine producer cells. In vivo induction of ThB function (leading to an optimal humoral response) in the absence of a cytokine-mediated inflammatory response could be of great potential in the development of vaccine strategies. We therefore studied the ThB cell activation requirements following a dendritic cell (DC)-based immunisation protocol in mice. Interestingly, we observed that DC kept in an 'immature' state were fully capable of promoting antigen specific antibody secretion in vivo, despite defective IFN induction. Eperiments are under way to assess the role of various factors (cytokines, transcription factors,') in the differentiation of naïve T cells towards the ThB cell type. These studies may lead to novel vaccination strategies inducing optimal antibody responses while minimizing local inflammatory reactions. [CD4+ T lymphocytes play a central role in antibody responses to T cell dependent antigens by activating B lymphocytes, promoting their survival and allowing affinity maturation and isotype switch. CD4+ T cells also control cell-mediated immune responses as well as allergic reactions. It is still unclear whether CD4+ T lymphocytes helping B cells represent a specialised sub-population or if they belong to a larger population having multiple functions. Recent data from the literature and vaccination studies suggest that CD4+ T cell-dependent antibody secretion by B lymphocytes could be dissociated from production of Th1 and Th2 cytokines. The aim of our project is to identify and characterize CD4+ T lymphocytes specialised in helping antibody production by B lymphocytes. As T helper cell for antibody secretion cannot be distinguished from naive T cells on a cytokine production-base data, we developed an in vitro test to directly detect their capacity to sustain an IgG class switch in B cell cooperation tests. This experimental setting allowed us to compare the B cell help activity mediated by distinct CD4+ T cell populations obtained following antigen inoculation in transgenic mice. Our results suggest that B helper T cells differ from both Th1 and Th2 cells and could therefore represent a 'new' CD4+ T cell population (ThB) distinct from the 'classical' Th1 and Th2 cytokine producer cells. In vivo induction of ThB function (leading to an optimal humoral response) in the absence of a cytokine-mediated inflammatory response could be of great potential in the development of vaccine strategies. We therefore studied the ThB cell activation requirements following a dendritic cell (DC)-based immunisation protocol in mice. Interestingly, we observed that DC kept in an 'immature' state were fully capable of promoting antigen specific antibody secretion in vivo, despite defective IFN induction. Experiments are under way to assess the role of various factors (cytokines, transcription factors,') in the differentiation of naïve T cells towards the ThB cell type. These studies may lead to novel vaccination strategies inducing optimal antibody responses while minimizing local inflammatory reactions.]