Toll-like receptor 5-deficient mice have dysregulated intestinal gene expression and nonspecific resistance to Salmonella-induced typhoid-like disease

The recognition of flagellin by Toll-like receptor 5 (TLR5) is the dominant means by which model intestinal epithelia activate proinflammatory gene expression in response to Salmonella enterica. The role of the flagellin-TLR5 interaction in vivo has been addressed primarily via studies that use flagellar mutants. Such studies suggest that host recognition of flagellin promotes rapid neutrophil recruitment that protects the host from this pathogen. However, these works do not directly address the role of TLR5 and are subject to the caveat that flagellar mutations may broadly affect Salmonella gene expression. Thus, we examined the role of the flagellin-TLR5 interaction via the use of TLR5-deficient (TLR5KO) mice. We utilized both the traditional model of murine Salmonella infection, wherein low-dose oral infection of mice with Salmonella enterica subsp. enterica serovar Typhimurium results in systemic typhoid-like disease, and a more recently characterized model in which mice are pretreated with streptomycin to result in gut-restricted acute enteritis. In the enteritis model, TLR5KO mice had more severe gut pathology, thus “phenocopying” previous results obtained with Salmonella mutants. In contrast, TLR5KO mice were resistant to Salmonella-induced typhoid-like disease. However, such resistance was not specific for flagellated serovar Typhimurium, but rather, TLR5KO mice were also resistant to challenges by flagellin-deficient serovar Typhimurium. Such resistance associated with elevations in the microbiota was ablated by antibiotic pretreatment and correlated with basal elevations in intestinal host defense gene expression. All together, these results indicate that the resistance of TLR5KO mice to Salmonella-induced typhoid-like illness resulted from alterations in their basal phenotype rather than from the lack of TLR5 ligation during the infection per se.     

Flagellin suppresses epithelial apoptosis and limits disease during enteric infection

Flagellin, the primary component of bacterial flagella, is a potent activator of toll-like receptor 5 (TLR5) signaling and is a major proinflammatory determinant of enteropathogenic Salmonella. In accordance with this, we report here that aflagellate Salmonella mutants are impaired in their ability to up-regulate proinflammatory and anti-apoptotic effector molecules in murine models of salmonellosis and that these mutants elicit markedly reduced early mucosal inflammation relative to their isogenic parent strains. Conversely, aflagellate bacteria were more potent activators of epithelial caspases and subsequent apoptosis. These phenomena correlated with a delayed but markedly exacerbated mucosal inflammation at the later stages of infection as well as elevated extra-intestinal and systemic bacterial load, culminating in a more severe clinical outcome. Systemic administration of exogenous flagellin primarily reversed the deleterious effects of in vivo Salmonella infection. These observations indicate that in Salmonella infection, flagellin plays a dominant role in activation of not only innate immunity but also anti-apoptotic processes in epithelial cells. These latter TLR-mediated responses that delay epithelial apoptosis may be as critical to mucosal defense as the classic acute inflammatory response. This notion is consistent with the emerging paradigm that specific TLR ligands may have a fundamental cytoprotective effect during inflammatory stress.     

Acute depletion of activated memory B cells involves the PD-1 pathway in rapidly progressing SIV-infected macaques

Rapid progression to AIDS is a significant problem, especially in developing countries, where the majority of HIV-infected individuals reside. As rapid disease progression is also frequently observed in SIV-infected macaques, they represent a valuable tool to investigate the pathogenesis of this condition in humans. Here, we have shown that pathogenic SIV infection in rhesus macaques resulted in a rapid depletion (as early as week 2) of activated memory B (CD21-CD27+; mBAct) cells that was strongly associated with rapid disease progression. This depletion was progressive and sustained in rapid progressors, but less severe and transient in typical progressors. Because of the rapid and sustained depletion of mBAct cells, rapid progressors failed to develop SIV-specific Ab responses, showed a decline in non-SIV-specific Ab titers, and succumbed faster to intestinal bacterial infections. Depletion of mBAct cells was strongly associated with preferential depletion of mBAct cells expressing programmed death-1 (PD-1), and in vitro blockade of PD-1 improved their survival. Furthermore, in vivo PD-1 blockade in SIV-infected macaques enhanced Ab responses to non-SIV as well as SIV Ags. Our results identify depletion of mBAct cells as a very early predictor of rapid disease progression in pathogenic SIV infection and suggest an important role for the PD-1 pathway in depletion of mBAct cells and impaired humoral immune responses in SIV-infected macaques.     

Activation of toll-like receptor 3 protects against DSS-induced acute colitis

BACKGROUND: Mimetics of bacterial DNA, given orally or subcutaneously, protect mice from experimental colitis via a toll-like receptor (TLR)-9-dependent mechanism. The goal of the study was to define whether synthetic viral RNA, polyinosinic acid:cytidylic acid [poly(I:C)], which is also a potent immunomodulator, might also affect murine colitis and, if so, define whether such effects were mediated by TLR3, which is one of at least 4 known receptors for this viral RNA analog. METHODS: Mice (C57BL6, IL-10KO, or TLR3 KO) were administered 1.5% dextran sodium sulfate (DSS) in drinking water for 7 days. Two hours before treatment with DSS, mice were given phosphate-buffered saline (PBS) or poly(I:C) 20 mug subcutaneously (s.c.), or 100 mug intragastrically (i.g.). RESULTS: In wildtype mice s.c. administration of poly(I:C) dramatically protected against DSS-induced colitis as assessed by every parameter analyzed, which included body weight, rectal bleeding, colonic myeloperoxidase, histopathology, serum keratinocyte-derived chemokine, serum amyloid A, and lipocalin-2. In contrast, i.g. administration of poly(I:C) offered no protection in this colitis model nor did its administration activate the innate immune system as assessed by serologic parameters. Subcutaneous poly(I:C) protected against DSS-induced colitis equally well in C57BL6 and IL-10KO mice, indicating that this antiinflammatory cytokine is not required for such protection. Protection against colitis given by poly(I:C) treatment was ablated in TLR3 KO, indicating that the protective action of this viral RNA analog was mediated by this receptor. CONCLUSIONS: Activation of TLR3 on cells that are accessible by systemic, but not oral, administration of synthetic viral RNA results in protection against the acute inflammation that can ensue upon damage of the gut epithelium. Thus, this viral RNA analog, which is under clinical trials for other inflammatory disorders (e.g., lupus), may also have therapeutic value for inflammatory bowel disease.     

Portuguese families with dentatorubropallidoluysian atrophy (DRPLA) share a common haplotype of Asian origin

Dentatorubropallidoluysian atrophy (DRPLA) is an autosomal dominant neurodegenerative disorder characterized by a variable combination of progressive ataxia, epilepsy, myoclonus, choreoathetosis and dementia. This disease is caused by a (CAG)(n) expansion in the DRPLA gene, on chromosome 12p13. DRPLA is prevalent in Japan, but several families of non-Japanese ancestry have already been published. To identify the origin of expanded alleles in Portuguese families with DRPLA, we studied two previously reported intragenic SNPs in introns 1 and 3, in addition to the CAG repeat of the DRPLA gene. The results showed that all four Portuguese DRPLA families shared the same haplotype, which is also common to that reported for Japanese DRPLA chromosomes. This haplotype is also the most frequent in Japanese normal alleles, whereas it was rare in Portuguese control chromosomes. Thus, our findings support that a founder DRPLA haplotype of Asian origin was introduced in Portugal, being responsible for the frequency of the disease in this country.