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OBJECTIVE To evaluate in vitro phagocytosis and bactericidal activity of circulating blood neutrophils in horses with severe equine asthma and control horses and to determine whether circulating blood neutrophils in horses with severe equine asthma have an increase in expression of the proinflammatory cytokine tumor necrosis factor (TNF)-α and the chemokine interleukin (IL)-8 and a decrease in expression of the anti-inflammatory cytokine IL-10 in response to bacteria. ANIMALS 6 horses with severe equine asthma and 6 control horses. PROCEDURES Circulating blood neutrophils were isolated from horses with severe equine asthma and control horses. Phagocytosis was evaluated by use of flow cytometry. Bactericidal activity of circulating blood neutrophils was assessed by use of Streptococcus equi and Streptococcus zooepidemicus as targets, whereas the cytokine mRNA response was assessed by use of a quantitative PCR assay. RESULTS Circulating blood neutrophils from horses with severe equine asthma had significantly lower bactericidal activity toward S zooepidemicus but not toward S equi, compared with results for control horses. Phagocytosis and mRNA expression of TNF-α, IL-8, and IL-10 were not different between groups. CONCLUSIONS AND CLINCAL RELEVANCE Impairment of bactericidal activity of circulating blood neutrophils in horses with severe equine asthma could contribute to an increased susceptibility to infections. [ABSTRACT FROM AUTHOR]

Abstract: The capsular polysaccharide is a critical virulence factor of the swine and zoonotic pathogen Streptococcus suis serotype 2. The capsule of this bacterium is composed of five different sugars, including terminal sialic acid. To evaluate the role of sialic acid in the pathogenesis of the infection, the neuC gene, encoding for an enzyme essential for sialic acid biosynthesis, was inactivated in a highly virulent S. suis serotype 2 strain. Using transmission electron microscopy, it was shown that inactivation of neuC resulted in loss of expression of the whole capsule. Compared to the parent strain, the ΔneuC mutant strain was more phagocytosed by macrophages and was also severely impaired in virulence in a mouse infection model. Both native and desialylated S. suis serotype 2 purified capsular polysaccharides were recognized by a polyclonal anti-whole cell S. suis serotype 2 serum and a monospecific polyclonal anti-capsule serotype 2 serum. In contrast, only the native capsular polysaccharide was recognized by a monoclonal antibody specific for the sialic acid moiety of the serotype 2 capsule. Together, our results infer that sialylation of S. suis serotype 2 may be essential for capsule expression, but that this sugar is not the main epitope of this serotype. [Copyright &y& Elsevier]

Streptococcus suis is an important swine pathogen and an emerging zoonotic agent of septicemia and meningitis. Knowledge on host immune responses towards S. suis, 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 S. suis 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 S. suis 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 S. suis internalization by DCs. This first study on receptors involved in DC activation by S. suis 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 S. suis. [ABSTRACT FROM AUTHOR]

Streptococcus suis is an emerging zoonotic agent of septicemia and meningitis. Knowledge on host immune responses toward S. suis and strategies used by this pathogen for subversion of these responses is scarce. Here, S. suis modulation of dendritic cell (DC) functions were assessed for the first time. Using S. suis knockout mutants in capsular polysaccharide (CPS) expression, it was shown that CPS blocks DC phagocytosis and impairs cytokine release by hindering cell wall components. Mutants impaired in D-alanylation of lipoteichoic acid (LTA) or N-deacetylation of peptidoglycan (PG) further demonstrated the importance of cell wall in modulation of DC activation. Notably, LTA/PG modifications were identified as major players in resistance to complement-dependent killing by DCs. Finally, S. suis hemolysin was partially involved in cytokine release and also contributed to bacterial escape of opsonophagocytosis. Overall, S. suis uses its arsenal of virulence factors to modulate DC functions and escape immune surveillance. [ABSTRACT FROM AUTHOR]

The pathogenesis of Streptococcus suis infection, a major swine and human pathogen, is only partially understood and knowledge on the host adaptive immune response is critically scarce. Yet, S. suis virulence factors, particularly its capsular polysaccharide (CPS), enable this bacterium to modulate dendritic cell (DC) functions and potentially impair the immune response. This study aimed to evaluate modulation of T cell activation during S. suis infection and the role of DCs in this response. S. suis-stimulated total mouse splenocytes readily produced TNF-α, IL-6, IFN-γ, CCL3, CXCL9, and IL-10. Ex vivo and in vivo analyses revealed the involvement of CD4+ T cells and a Th1 response. Nevertheless, during S. suis infection, levels of the Th1-derived cytokines TNF-α and IFN-γ were very low. A transient splenic depletion of CD4+ T cells and a poor memory response were also observed. Moreover, CD4+ T cells secreted IL-10 and failed to up-regulate optimal levels of CD40L and CD69 in coculture with DCs. The CPS hampered release of several T cell-derived cytokines in vitro. Finally, a correlation was established between severe clinical signs of S. suis disease and impaired antibody responses. Altogether, these results suggest S. suis interferes with the adaptive immune response. [ABSTRACT FROM AUTHOR]

Abstract: Group B Streptococcus (GBS) type III is an important agent of life-threatening invasive infections. Albeit the immune system plays a dual role in development and protection against disease, mechanisms leading to an efficient immune response against GBS remain obscure. Mouse bone marrow-derived dendritic cells (DCs) and primary spleen DCs were used to evaluate GBS capacity to modulate the functions of these important antigen-presenting cells. The role of capsular polysaccharide (CPS), one of the most important GBS virulence factors, in bacterial-DC interactions was evaluated by using a non-encapsulated mutant. Phagocytosis assays, confocal and electron microscopy showed that DCs efficiently internalize encapsulated GBS, but the latter possesses strong intracellular survival capacity. GBS devoid of CPS was internalized and killed at higher and faster rates than encapsulated GBS early after infection. Among several cytokines tested, GBS internalization was required for modulation of IL-12, IL-10 and CXCL10 pathways. In contrast, GBS induced DC expression of co-stimulatory molecules in a phagocytosis-independent manner. Finally, the production of pro-inflammatory and Th1 cytokines by GBS-stimulated DCs was differentially modulated by CPS expression, depending on DC origin. Our data suggest multiple mechanisms involved in GBS modulation of DC functions, which were selectively regulated by the presence of CPS. [Copyright &y& Elsevier]

Abstract: Infections caused by Streptococcus suis are an important economic problem in the swine industry. Moreover, S. suis (especially serotype 2) is an agent of zoonosis that has the potential to afflict those who are in close contact with infected pigs or pork-derived products. Although sporadic cases of S. suis infections in humans have been reported during the last 40 years, a large outbreak occurred in China in 2005. The severity of the infection in humans during the outbreak, such as clinical signs of streptococcal toxic shock syndrome, attracted much attention from the scientific community and the public press. In part I of this article, the general characteristics of the organism were reviewed, as well as the clinical characteristics associated with S. suis infection in humans, the pathogenesis of infection and associated virulence factors, and finally, the interactions between S. suis and the host''s immune system. Part II of this series focuses on the epidemiology of S. suis infections in humans, as well as a discussion of the possible explanations to account for the geographic differences in human infections caused by this organism. [Copyright &y& Elsevier]

Abstract: Infections caused by Streptococcus suis are an important economic problem in the swine industry. Moreover, S. suis (especially serotype 2) is an agent of zoonosis that has the potential to afflict those who are in close contact with infected pigs or pork-derived products. Although sporadic cases of S. suis infections in humans have been reported during the last 40 years, a large outbreak in China emerged in 2005. The severity of the infection in humans during the outbreak, such as clinical signs of streptococcal toxic shock syndrome, attracted much attention from the scientific community and the public press. This two-part review will focus on this organism and the infections it causes, highlighting the differences between Asian and Western countries, particularly with respect to its epidemiology. In part I, the general characteristics of the organism are reviewed, as well as the clinical characteristics associated with S. suis infection in humans, the pathogenesis of infection and associated virulence factors, and, finally, the interactions between S. suis and the host''s immune system. [Copyright &y& Elsevier]

Abstract: Streptococcus suis is a major pathogen of swine, causing mainly meningitis, and it also represents an emerging zoonotic agent. We investigated its ability to induce the release of pro-inflammatory cytokines and chemokines by porcine brain microvascular endothelial cells (PBMEC). We demonstrated that live S. suis induced a strong release of interleukin (IL)-6 and IL-8 by PBMEC. We showed that the suilysin (hemolysin) was largely responsible for such stimulation, although cell wall components also contribute to cell stimulation but to a considerably lower extent. Interestingly, IL-8 production by PBMEC became undetectable by increasing either the incubation time or bacterial concentration of certain live S. suis strains. We further demonstrated that this decrease of IL-8 levels was probably linked to the production of a serine protease by S. suis. Our results suggest that S. suis can induce an exacerbated release of inflammatory mediators by swine endothelial cells that could cause a massive recruitment of leukocytes and subsequent blood–brain barrier breakdown facilitating the pathogenesis of S. suis-induced meningitis. In addition, S. suis could modulate this response by degrading IL-8 which might delay recruitment of S. suis killer-neutrophils to the site of inflammation, allowing this pathogen to survive upon its arrival to central nervous system. [Copyright &y& Elsevier]

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. [ABSTRACT FROM AUTHOR]

Abstract: 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 24h 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 24hpi 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 24hpi, 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. [Copyright &y& Elsevier]

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 59 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. [ABSTRACT FROM AUTHOR]