Rôle des cellules dendritiques dans la modulation de la réponse immunitaire de l'hôte contre Streptococcus suis

Streptococcus suis est un important pathogène porcin et agent zoonotique responsable de méningites et de septicémies. À ce jour, les mécanismes impliqués dans la réponse immunitaire de l’hôte lors de l’infection par S. suis sont peu connus; et il en est de même pour les stratégies utilisées par S. suis afin de déjouer cette réponse. L’augmentation de l’incidence et de la sévérité des cas humains souligne le besoin d’une meilleure compréhension des interactions entre S. suis et le système immunitaire afin de générer une réponse immunitaire efficace contre ce pathogène. Les cellules dendritiques (DCs) sont de puissantes cellules présentatrices d’antigènes qui stimulent les lymphocytes T et B, assurant la liaison entre l’immunité innée et l’immunité adaptative. L’objectif principal de ce projet était d’évaluer le rôle joué par différents facteurs de virulence de S. suis sur la modulation de la fonction des DCs et de la réponse T-dépendante. Nous avons examiné l’effet des facteurs clés pour la virulence de S. suis, dont la capsule polysaccharidique (CPS), les modifications de la paroi cellulaire (D-alanylation de l’acide lipotéichoïque et N-déacétylation du peptidoglycane) et la toxine suilysine, sur l’activation et la maturation de DCs murines dérivées de la moelle osseuse (bmDCs). Suite à l’infection par S. suis, les bmDCs sont activées et subissent un processus de maturation caractérisé par l’augmentation de l’expression de molécules de co-stimulation et la production de cytokines pro-inflammatoires. La CPS est le principal facteur interférant avec la production de cytokines, même si les modifications de la paroi cellulaire et la suilysine peuvent également moduler la production de certaines cytokines. Enfin, la CPS, les modifications de la paroi cellulaire et la suilysine interfèrent avec la déposition du complément à la surface des bactéries et, en conséquence, avec le « killing » dépendant du complément. Les résultats ont été confirmés à l’aide de bmDCs porcines. Nous avons aussi voulu identifier les récepteurs cellulaires impliqués dans la reconnaissance de S. suis par les DCs. Nous avons démontré que la production de cytokines et l’expression des molécules de co-stimulation par les DCs sont fortement dépendantes de la signalisation par MyD88, suggérant que les DCs reconnaissent S. suis et deviennent activées majoritairement via la signalisation par les récepteurs de type Toll (TLRs). En effet, on remarque une diminution de la production de plusieurs cytokines ainsi que de l’expression de certaines molécules de co-stimulation chez les DCs TLR2-/- ou TLR2-/- et TLR9-/- double négatives. Finalement, le récepteur NOD2 semblait jouer un rôle partiel dans l’activation des DCs suite à une infection par S. suis.Enfin, nous avons évalué les conséquences de la modulation des fonctions des DCs sur le développement de la réponse T-dépendante. Les splénocytes totaux produisent plusieurs cytokines en réponse à S. suis. Des analyses in vivo et ex vivo ont permis d’observer l’implication des cellules T CD4+ et le développement d’une réponse de type « T helper » 1 (TH1) bien que la quantité de cytokines TH1 produites lors de l’infection in vivo par S. suis demeure assez basse. La CPS de S. suis interfère avec la production de plusieurs cytokines par les cellules T in vitro. Expérimentalement, l’infection induite par S. suis résulte en de faibles niveaux de production d’anticorps anti-S. suis, mais aussi d’anticorps dirigés contre l’ovalbumine utilisée comme antigène rapporteur. Cette interférence est corrélée avec la sévérité des signes cliniques, suggérant que S. suis interfère avec le développement d’une réponse immunitaire adaptative appropriée qui serait requise pour contrôler la progression de l’infection. Les résultats de cette étude mèneront à une meilleure compréhension de la réponse immunitaire de l’hôte lors de l’infection par S. suis.Streptococcus suis is an important swine pathogen and an emerging zoonotic agent of septicemia and meningitis. Knowledge of host immune responses towards S. suis, and strategies used by this pathogen for subversion of these responses is scarce. Increased severity of S. suis infections in humans underscores the critical need to better understand the interactions between S. suis and the immune system to generate an effective immune response against this pathogen. Dendritic cells (DCs) are powerful antigen-presenting cells. Once activated, they stimulate T cells and B cells, linking innate and adaptive immunity. Thus, the main objective of this project was to evaluate the role of different S. suis virulence factors on the modulation of DC functions and the T cell-dependent response. Initially, we investigated the effect of S. suis key virulence factors, including the capsular polysaccharide (CPS), the cell wall modifications (D-alanylation of the lipoteichoic acid and N-deacetylation of the peptidoglycan) and the toxin suilysin, on the activation and maturation of mouse bone-marrow derived DCs (bmDCs). We observed that following S. suis infection, bmDCs are activated and go through a complex maturation process characterized by the up-regulation of the surface expression of costimulatory molecules and the production of pro-inflammatory cytokines. The CPS is the main virulence factor interfering with cytokine production, even if cell wall modifications and suilysin can also modulate the production of cytokines. Finally, CPS, cell wall modifications and suilysin were shown to interfere with complement deposition on S. suis, and consequently with complement-dependent killing. Results were confirmed using porcine bmDCs. We also aimed to identify the cellular receptors involved in S. suis recognition by DCs. Production of cytokines and expression of co-stimulatory molecules by DCs were shown to strongly rely on MyD88-dependent signaling pathways, suggesting that DCs recognize S. suis and become activated mostly through Toll-like receptor (TLR) signaling. Supporting this fact, TLR2-/- or double negative TLR2-/- and TLR9-/- DCs were severely impaired in the release of several cytokines and the surface expression of certain costimulatory molecules. In addition, NOD2 receptor also seems to play a partial role in DC activation by S. suis. Finally, we evaluated the consequences of the modulation of DC functions on T cell activation. In response to S. suis infection, total splenocytes readily produced several cytokines ex vivo. Ex vivo and in vivo analysis revealed the involvement of CD4+ T cells and development of a T helper 1 (TH1) response. Nevertheless, levels of TH1-derived cytokines during S. suis infection were very low. The bacterial CPS was shown to interfere with the release of several T cell-derived cytokines in vitro. As a consequence, a clinical infection resulted in low levels of not only anti-S. suis antibodies but also of those directed against ovalbumin, used as reported antigen. This interference was correlated with the presence of severe clinical signs of S. suis disease. These data suggest that S. suis impairs the development of an efficient adaptive immune response, which is required to control the infection progress. Overall, these results will permit a better comprehension of the host immune response during S. suis infection

Characterization of porcine dendritic cell response to Streptococcus suis

Streptococcus suis is a major swine pathogen and important zoonotic agent causing mainly septicemia and meningitis. However, the mechanisms involved in host innate and adaptive immune responses toward S. suis as well as the mechanisms used by S. suis to subvert these responses are unknown. Here, and for the first time, the ability of S. suis to interact with bone marrow-derived swine dendritic cells (DCs) was evaluated. In addition, the role of S. suis capsular polysaccharide in modulation of DC functions was also assessed. Well encapsulated S. suis was relatively resistant to phagocytosis, but it increased the relative expression of Toll-like receptors 2 and 6 and triggered the release of several cytokines by DCs, including IL-1β, IL-6, IL-8, IL-12p40 and TNF-α. The capsular polysaccharide was shown to interfere with DC phagocytosis; however, once internalized, S. suis was readily destroyed by DCs independently of the presence of the capsular polysaccharide. Cell wall components were mainly responsible for DC activation, since the capsular polysaccharide-negative mutant induced higher cytokine levels than the wild-type strain. The capsular polysaccharide also interfered with the expression of the co-stimulatory molecules CD80/86 and MHC-II on DCs. To conclude, our results show for the first time that S. suis interacts with swine origin DCs and suggest that these cells might play a role in the development of host innate and adaptive immunity during an infection with S. suis serotype 2

Mutations in the Gene Encoding the Ancillary Pilin Subunit of the Streptococcus suis srtF Cluster Result in Pili Formed by the Major Subunit Only

Pili have been shown to contribute to the virulence of different Gram-positive pathogenic species. Among other critical steps of bacterial pathogenesis, these structures participate in adherence to host cells, colonization and systemic virulence. Recently, the presence of at least four discrete gene clusters encoding putative pili has been revealed in the major swine pathogen and emerging zoonotic agent Streptococcus suis. However, pili production by this species has not yet been demonstrated. In this study, we investigated the functionality of one of these pili clusters, known as the srtF pilus cluster, by the construction of mutant strains for each of the four genes of the cluster as well as by the generation of antibodies against the putative pilin subunits. Results revealed that the S. suis serotype 2 strain P1/7, as well as several other highly virulent invasive S. suis serotype 2 isolates express pili from this cluster. However, in most cases tested, and as a result of nonsense mutations at the 5′ end of the gene encoding the minor pilin subunit (a putative adhesin), pili were formed by the major pilin subunit only. We then evaluated the role these pili play in S. suis virulence. Abolishment of the expression of srtF cluster-encoded pili did not result in impaired interactions of S. suis with porcine brain microvascular endothelial cells. Furthermore, non-piliated mutants were as virulent as the wild type strain when evaluated in a murine model of S. suis sepsis. Our results show that srtF cluster-encoded, S. suis pili are atypical compared to other Gram-positive pili. In addition, since the highly virulent strains under investigation are unlikely to produce other pili, our results suggest that pili might be dispensable for critical steps of the S. suis pathogenesis of infection

Qu’est-ce que le professionnalisme en ergothérapie ? Étude des représentations d’étudiants et de superviseurs de stagiaires francophones du Québec

Le professionnalisme est une compétence-clé pour les ergothérapeutes, mais des enjeux d’ambiguïté concernant sa définition ont été soulevés par le passé. Une récente étude a permis de proposer une définition contemporaine du professionnalisme en ergothérapie. Or, cette définition est générique et ne tient pas compte des spécificités de la population particulière que sont les étudiants en ergothérapie. Le but de cette étude était d’explorer les représentations sociales qu’ont du professionnalisme des étudiants et des superviseurs de stagiaires en ergothérapie dans le contexte universitaire francophone québécois. Selon un devis descriptif interprétatif, des groupes de discussion ont été menés auprès de 16 étudiants universitaires et des entrevues individuelles ont été conduites avec 16 superviseurs de stagiaires. Les données qualitatives recueillies ont été traitées à l’aide d’une stratégie d’analyse thématique. Il s’agissait de déterminer les antécédents (p. ex. : parcours éducatif), attributs (p. ex. : attitude de juste confiance en soi ou comportement consistant à considérer tous les membres de l’équipe de façon égalitaire) et conséquents (p. ex. : identité professionnelle) du professionnalisme en ergothérapie qui soient spécifiques à la population des étudiants et des superviseurs francophones en ergothérapie au Québec. Il ressort des résultats que le professionnalisme s’inscrit dans un paradigme développemental complexe, que les valeurs propres à la profession sont peu présentes dans les représentations sociales des étudiants et superviseurs de stagiaires rencontrés et que l’organisation du travail peut être une menace pour le professionnalisme en ergothérapie. Enfin, cette étude offre des leviers sur lesquels agir pour faciliter et bonifier l’enseignement et le développement du professionnalisme, notamment en suggérant de miser sur les activités réflexives (p. ex. : portfolio) et d’échange (p. ex. : communauté de pratique) et de bonifier la formation en éthique que reçoivent les étudiants. ______________________________________________________________________________________________________________________________ Professionalism is a key competency for occupational therapists, but issues of ambiguity regarding its definition have arisen in the past. A recent study proposed a contemporary definition of professionalism in occupational therapy. However, this definition is generic and does not consider the specifics of the singular population of occupational therapy students. The purpose of this study was to explore the social representations of professionalism of students and supervisors of occupational therapy interns in the francophone university context in Quebec. According to an interpretative descriptive research design, focus groups were conducted with 16 university students and individual interviews were conducted with 16 supervisors of interns. The qualitative data collected was processed using a thematic analysis strategy. Results suggest antecedents (e.g.: academic background), attributes (e.g.: attitude of fair self-confidence or behavior of considering all team members equally) and consequences (e.g.: professional identity) of professionalism in occupational therapy that are unique to the population of French-speaking occupational therapy students and intern supervisors in Quebec. The interpretation of the results suggests that professionalism is part of a complex developmental paradigm, that the values specific to the profession are not very present in the social representations of the students and intern supervisors we met, and that the work organization may be a threat to professionalism in occupational therapy. Finally, this study offers levers to facilitate and improve the teaching and development of professionalism, notably by suggesting that reflective activities (e.g.: portfolios), exchange activities (e.g.: community of practice) and ethics training for students be enhanced

Qu’est-ce que le professionnalisme en ergothérapie ? Étude des représentations d’étudiants et de superviseurs de stagiaires francophones du Québec

Le professionnalisme est une compétence-clé pour les ergothérapeutes, mais des enjeux d’ambiguïté concernant sa définition ont été soulevés par le passé. Une récente étude a permis de proposer une définition contemporaine du professionnalisme en ergothérapie. Or, cette définition est générique et ne tient pas compte des spécificités de la population particulière que sont les étudiants en ergothérapie. Le but de cette étude était d’explorer les représentations sociales qu’ont du professionnalisme des étudiants et des superviseurs de stagiaires en ergothérapie dans le contexte universitaire francophone québécois. Selon un devis descriptif interprétatif, des groupes de discussion ont été menés auprès de 16 étudiants universitaires et des entrevues individuelles ont été conduites avec 16 superviseurs de stagiaires. Les données qualitatives recueillies ont été traitées à l’aide d’une stratégie d’analyse thématique. Il s’agissait de déterminer les antécédents (p. ex. : parcours éducatif), attributs (p. ex. : attitude de juste confiance en soi ou comportement consistant à considérer tous les membres de l’équipe de façon égalitaire) et conséquents (p. ex. : identité professionnelle) du professionnalisme en ergothérapie qui soient spécifiques à la population des étudiants et des superviseurs francophones en ergothérapie au Québec. Il ressort des résultats que le professionnalisme s’inscrit dans un paradigme développemental complexe, que les valeurs propres à la profession sont peu présentes dans les représentations sociales des étudiants et superviseurs de stagiaires rencontrés et que l’organisation du travail peut être une menace pour le professionnalisme en ergothérapie. Enfin, cette étude offre des leviers sur lesquels agir pour faciliter et bonifier l’enseignement et le développement du professionnalisme, notamment en suggérant de miser sur les activités réflexives (p. ex. : portfolio) et d’échange (p. ex. : communauté de pratique) et de bonifier la formation en éthique que reçoivent les étudiants. ______________________________________________________________________________________________________________________________ Professionalism is a key competency for occupational therapists, but issues of ambiguity regarding its definition have arisen in the past. A recent study proposed a contemporary definition of professionalism in occupational therapy. However, this definition is generic and does not consider the specifics of the singular population of occupational therapy students. The purpose of this study was to explore the social representations of professionalism of students and supervisors of occupational therapy interns in the francophone university context in Quebec. According to an interpretative descriptive research design, focus groups were conducted with 16 university students and individual interviews were conducted with 16 supervisors of interns. The qualitative data collected was processed using a thematic analysis strategy. Results suggest antecedents (e.g.: academic background), attributes (e.g.: attitude of fair self-confidence or behavior of considering all team members equally) and consequences (e.g.: professional identity) of professionalism in occupational therapy that are unique to the population of French-speaking occupational therapy students and intern supervisors in Quebec. The interpretation of the results suggests that professionalism is part of a complex developmental paradigm, that the values specific to the profession are not very present in the social representations of the students and intern supervisors we met, and that the work organization may be a threat to professionalism in occupational therapy. Finally, this study offers levers to facilitate and improve the teaching and development of professionalism, notably by suggesting that reflective activities (e.g.: portfolios), exchange activities (e.g.: community of practice) and ethics training for students be enhanced

Swine, human or avian influenza viruses differentially activates porcine dendritic cells cytokine profile

Swine influenza virus (SwIV) is considered a zoonosis and the fact that swine may act as an intermediate reservoir for avian influenza virus, potentially infectious for humans, highlights its relevance and the need to understand the interaction of different influenza viruses with the porcine immune system. Thus, in vitro porcine bone marrow-derived dendritic cell (poBMDCs) were infected with a circulating SwIV A/Swine/Spain/SF32071/2007(H3N2), 2009 human pandemic influenza virus A/Catalonia/63/2009(H1N1), low pathogenic avian influenza virus (LPAIV) A/Anas plathyrhynchos/Spain/1877/2009(aH7N2) or high pathogenic avian influenza virus (HPAIV) A/Chicken/Italy/5093/1999(aH7N1). Swine influenza virus H3N2 infection induced an increase of SLA-I and CD80/86 at 16 and 24 h post infection (hpi), whereas the other viruses did not. All viruses induced gene expression of NF-κB, TGF-β, IFN-β and IL-10 at the mRNA level in swine poBMDCs to different extents and in a time-dependent manner. All viruses induced the secretion of IL-12 mostly at 24 hpi whereas IL-18 was detected at all tested times. Only swH3N2 induced IFN-α in a time-dependent manner. Swine H3N2, aH7N2 and aH7N1 induced secretion of TNF-α also in a time-dependent manner. Inhibition of NF-κB resulted in a decrease of IFN-α and IL-12 secretion by swH3N2-infected poBMDC at 24 hpi, suggesting a role of this transcription factor in the synthesis of these cytokines. Altogether, these data might help in understanding the relationship between influenza viruses and porcine dendritic cells in the innate immune response in swine controlled through soluble mediators and transcription factors.This work was partly funded by the Project No. CSD 2006-00007, AGL2006-13809-C03-01, AGL2009-12945-C02-01 and AGL2010-22200-C02-01 by the Spanish Government. PhD studies of Mrs. Tufária Mussá and Masssimiliano Baratelli are funded by doctoral grants from the AECID and MICIN respectively.Peer reviewe

Group B Streptococcus Induces a Robust IFN-γ Response by CD4+ T Cells in an In Vitro and In Vivo Model

Group B Streptococcus (GBS) serotype III causes life-threatening infections. Cytokines have emerged as important players for the control of disease, particularly IFN-γ. Although potential sources of this cytokine have been proposed, no specific cell line has ever been described as a leading contributor. In this study, CD4+ T cell activation profiles in response to GBS were evaluated through in vivo, ex vivo, and in vitro approaches. Total splenocytes readily produce a type 1 proinflammatory response by releasing IFN-γ, TNF-α, and IL-6 and actively recruit T cells via chemokines like CXCL9, CXCL10, and CCL3. Responding CD4+ T cells differentiate into Th1 cells producing large amounts of IFN-γ, TNF-α, and IL-2. In vitro studies using dendritic cell and CD4+ T cell cocultures infected with wild-type GBS or a nonencapsulated mutant suggested that GBS capsular polysaccharide, one of the major bacterial virulence factors, differentially modulates surface expression of CD69 and IFN-γ production. Overall, CD4+ T cells are important producers of IFN-γ and might thus influence the course of GBS infection through the expression balance of this cytokine

Immune Receptors Involved in <em>Streptococcus suis</em> Recognition by Dendritic Cells

<div><p><em>Streptococcus suis</em> is an important swine pathogen and an emerging zoonotic agent of septicemia and meningitis. Knowledge on host immune responses towards <em>S. suis</em>, and strategies used by this pathogen for subversion of these responses is scarce. The objective of this study was to identify the immune receptors involved in <em>S. suis</em> recognition by dendritic cells (DCs). Production of cytokines and expression of co-stimulatory molecules by DCs were shown to strongly rely on MyD88-dependent signaling pathways, suggesting that DCs recognize <em>S. suis</em> and become activated mostly through Toll-like receptor (TLR) signaling. Supporting this fact, TLR2^−/− DCs were severely impaired in the release of several cytokines and the surface expression of CD86 and MHC-II. The release of IL-12p70 and CXC10, and the expression of CD40 were found to depend on signaling by both TLR2 and TLR9. The release of IL-23 and CXCL1 were partially dependent on NOD2. Finally, despite the fact that MyD88 signaling was crucial for DC activation and maturation, MyD88-dependent pathways were not implicated in <em>S. suis</em> internalization by DCs. This first study on receptors involved in DC activation by <em>S. suis</em> suggests a major involvement of MyD88 signaling pathways, mainly (but not exclusively) through TLR2. A multimodal recognition involving a combination of different receptors seems essential for DC effective response to <em>S. suis</em>.</p> </div