T-cell response against varicella-zoster virus in fingolimod-treated MS patients.

OBJECTIVE: To study the immune response against varicella-zoster virus (VZV) in patients with multiple sclerosis before and during fingolimod therapy. METHODS: The VZV-specific immune response was studied using interferon (IFN)-γ enzyme-linked immunosorbent spot assay, proliferation assays, and upregulation of T-cell activation markers in patients before (n = 38) and after 3 months of fingolimod therapy (n = 34), in untreated (n = 33) and IFN-ß-treated (n = 25) patients with multiple sclerosis, and in healthy controls (n = 22). Viral replication was analyzed by using real-time PCR in 76 peripheral blood mononuclear cell samples and 146 saliva samples. RESULTS: Treatment with fingolimod led to a marked reduction of CD3(+) T cells with a relative decrease of naive and central memory T cells and an increase of effector memory T cells. Expression of the activation markers CD137 and CD69 upon VZV stimulation was unaltered by fingolimod. However, the absolute number of cells proliferating upon VZV stimulation was reduced in the blood of patients treated with fingolimod. Also, VZV-specific and Epstein-Barr virus (EBV)-specific IFN-γ-producing cells were reduced after fingolimod therapy. Seven of the 35 patients treated with fingolimod showed signs of VZV or EBV reactivation in saliva compared with 3 of the 111 controls. None of the 76 tested samples showed signs of viral reactivation in the peripheral blood mononuclear cells. CONCLUSION: Patients treated with fingolimod show a slightly reduced antiviral T-cell response. This reduced response is accompanied by a subclinical reactivation of VZV or EBV in the saliva of 20% of patients treated with fingolimod.

Resistance of Capnocytophaga canimorsus to killing by human complement and polymorphonuclear leukocytes.

Capnocytophaga canimorsus is a bacterium of the canine oral flora known since 1976 to cause rare but severe septicemia and peripheral gangrene in patients that have been in contact with a dog. It was recently shown that these bacteria do not elicit an inflammatory response (H. Shin, M. Mally, M. Kuhn, C. Paroz, and G. R. Cornelis, J. Infect. Dis. 195:375-386, 2007). Here, we analyze their sensitivity to the innate immune system. Bacteria from the archetype strain Cc5 were highly resistant to killing by complement. There was little membrane attack complex (MAC) deposition in spite of C3b deposition. Cc5 bacteria were as resistant to phagocytosis by human polymorphonuclear leukocytes (PMNs) as Yersinia enterocolitica MRS40, endowed with an antiphagocytic type III secretion system. We isolated Y1C12, a transposon mutant that is hypersensitive to killing by complement via the antibody-dependent classical pathway. The mutation inactivated a putative glycosyltransferase gene, suggesting that the Y1C12 mutant was affected at the level of a capsular polysaccharide or lipopolysaccharide (LPS) structure. Cc5 appeared to have several polysaccharidic structures, one being altered in Y1C12. The structure missing in Y1C12 could be purified by classical LPS purification procedures and labeled by tritiated palmitate, indicating that it is more likely to be an LPS structure than a capsule. Y1C12 bacteria were also more sensitive to phagocytosis by PMNs than wild-type bacteria. In conclusion, a polysaccharide structure, likely an LPS, protects C. canimorsus from deposition of the complement MAC and from efficient phagocytosis by PMNs.

Prevalence of Capnocytophaga canimorsus in dogs and occurrence of potential virulence factors.

Capnocytophaga canimorsus is a Gram-negative commensal of dog's mouth causing severe human infections. A strain isolated from a human fatal infection was recently shown to have a sialidase, to inhibit the bactericidal activity of macrophages and to block the release of nitric oxide by LPS-stimulated macrophages. The present study aimed at determining the prevalence of C. canimorsus in dogs and the occurrence of these hypothetical virulence factors. C. canimorsus could be retrieved from the saliva of 61 dogs out of 106 sampled. Like in clinical isolates, all dog strains had a sialidase and 60% blocked the killing of phagocytosed Escherichia coli by macrophages. In contrast, only 6.5% of dog strains blocked the release of nitric oxide by LPS-challenged macrophages, suggesting that this property might contribute to virulence. The comparative analysis of 69 16S rDNA sequences revealed the existence of C. canimorsus strains that could be misdiagnosed.

Capnocytophaga canimorsus: a human pathogen feeding at the surface of epithelial cells and phagocytes.

Capnocytophaga canimorsus, a commensal bacterium of the canine oral flora, has been repeatedly isolated since 1976 from severe human infections transmitted by dog bites. Here, we show that C. canimorsus exhibits robust growth when it is in direct contact with mammalian cells, including phagocytes. This property was found to be dependent on a surface-exposed sialidase allowing C. canimorsus to utilize internal aminosugars of glycan chains from host cell glycoproteins. Although sialidase probably evolved to sustain commensalism, by releasing carbohydrates from mucosal surfaces, it also contributed to bacterial persistence in a murine infection model: the wild type, but not the sialidase-deficient mutant, grew and persisted, both when infected singly or in competition. This study reveals an example of pathogenic bacteria feeding on mammalian cells, including phagocytes by deglycosylation of host glycans, and it illustrates how the adaptation of a commensal to its ecological niche in the host, here the dog's oral cavity, contributes to being a potential pathogen.

Escape from immune surveillance by Capnocytophaga canimorsus.

Capnocytophaga canimorsus, a commensal bacterium from dogs' mouths, can cause septicemia or meningitis in humans through bites or scratches. Here, we describe and characterize the inflammatory response of human and mouse macrophages on C. canimorsus infection. Macrophages infected with 10 different strains failed to release tumor necrosis factor (TNF)- alpha and interleukin (IL)-1 alpha . Macrophages infected with live and heat-killed (HK) C. canimorsus 5 (Cc5), a strain isolated from a patient with fatal septicemia, did not release IL-6, IL-8, interferon- gamma , macrophage inflammatory protein-1 beta , and nitric oxide (NO). This absence of a proinflammatory response was characterized by the inability of Toll-like receptor (TLR) 4 to respond to Cc5. Moreover, live but not HK Cc5 blocked the release of TNF- alpha and NO induced by HK Yersinia enterocolitica. In addition, live Cc5 down-regulated the expression of TLR4 and dephosphorylated p38 mitogen-activated protein kinase. These results highlight passive and active mechanisms of immune evasion by C. canimorsus, which may explain its capacity to escape from the host immune system.

Expressed isolated integrin beta1 subunit cytodomain induces endothelial cell death secondary to detachment.

Expression of isolated beta integrin cytoplasmic domains in cultured endothelial cells was reported to induce cell detachment and death. To test whether cell death was the cause or the consequence of cell detachment, we expressed isolated integrin beta1 cytoplasmic and transmembrane domains (CH1) in cultured human umbilical vein endothelial cells (HUVEC), and monitored detachment, viability, caspase activation and signaling. CH1 expression induced dose-dependent cell detachment. At 24 h over 90% of CH1-expressing HUVEC were detached but largely viable (>85%). No evidence of pro-caspase-8,-3, and PARP cleavage or suppression of phosphorylation of ERK, PKB and Ikappa-B was observed. The caspase inhibitor z-VAD did not prevent cell detachment. At 48 h, however, CH1-expressing cells were over 50% dead. As a comparison trypsin-mediated detachment resulted in a time-dependent cell death, paralleled by caspase-3 activation and suppression of ERK, PKB and Ikappa-B phosphoyrylation at 24 h or later after detachment. HUVEC stimulation with agents that strengthen integrin-mediated adhesion (i.e. PMA, the Src inhibitor PP2 and COMP-Ang1) did not prevent CH1-induced detachment. Expression of CH1 in rat carotid artery endothelial cells in vivo caused endothelial cell detachment and increased nuclear DNA fragmentation among detached cells. A construct lacking the integrin cytoplasmic domain (CH2) had no effect on adhesion and cell viability in vitro and in vivo. These results demonstrate that isolated beta1 cytoplasmic domain expression induces caspase-independent detachment of viable endothelial cells and that death is secondary to detachment (i.e. anoikis). They also reveal an essential role for integrins in the adhesion and survival of quiescent endothelial cells in vivo.

Secretion of YscP from Yersinia enterocolitica is essential to control the length of the injectisome needle but not to change the type III secretion substrate specificity.

The length of the needle of the Yersinia Ysc injectisome is determined by a protein called YscP. This protein, which acts both as a molecular ruler and as a substrate-specificity switch for type III secretion is itself secreted by the injectisome. In this report, we address the question why YscP is secreted. By a systematic deletion analysis and by fusing different parts of the molecule to the adenylate cyclase reporter, we identified two independent secretion signals. One of them is encompassed within the 35 N-terminal residues while the second one spans residues 97-137. These two signals are functionally different from Yop secretion signals. When both secretion signals were removed, Yops could still be secreted but the needle length control was lost. YscP possessing only one signal did not control needle length properly but the control was improved when more YscP was produced and secreted. YscP deprived of both signals could not control length, even when overproduced. We conclude from this that YscP needs to be secreted to exert its length control function but not its substrate-specificity switch function.

Characterization of a Type III secretion substrate specificity switch (T3S4) domain in YscP from Yersinia enterocolitica.

The length of the needle ending the Yersinia Ysc injectisome is determined by YscP, a protein acting as a molecular ruler. In addition, YscP is required for Yop secretion. In the present paper, by a systematic deletion analysis, we localized accurately the region required for Yop secretion between residues 405 and 500. As this C-terminal region of YscP has also been shown to control needle length it probably represents the substrate specificity switch of the machinery. By a bioinformatics analysis, we show that this region has a globular structure, an original alpha/beta fold, a P-x-L-G signature and presumably no catalytic activity. In spite of very limited sequence similarities, this structure is conserved among the proteins that are presumed to control the needle length in many different injectisomes and also among members of the FliK family, which control the flagellar hook length. This region thus represents a new protein domain that we called T3S4 for Type III secretion substrate specificity switch. The T3S4 domain of YscP can be replaced by the T3S4 domain of AscP (Aeromonas salmonicida) or PscP (Pseudomonas aeruginosa) but not by the one from FliK, indicating that in spite of a common global structure, these domains need to fit their partner proteins in the secretion apparatus.