Browsing publications of the research group immunology of infection ([HZI]INI) by Subject (MeSH)
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Age-related susceptibility to Streptococcus pyogenes infection in mice: underlying immune dysfunction and strategy to enhance immunity.Epidemiological studies have shown that the elderly are at higher risk of severe Streptococcus pyogenes infections. In this study, we used a mouse model that displays the age-related loss of resistance to S. pyogenes infection seen in humans to investigate the impaired immune mechanism underlying the age-associated susceptibility to this pathogen. Young (2-3 months old) and aged (>20 months old) BALB/c mice were subcutaneously or intravenously inoculated with S. pyogenes and their capacity to control infection was compared. Aged mice showed faster progression of disease, earlier morbidity, and increased mortality when compared with young animals. Since macrophages are critical for host defence against S. pyogenes, we investigated whether susceptibility of aged mice may be due to an age-associated decline in the functionality of these cells. Our results showed that macrophages from aged mice were as capable as those from young animals to uptake and kill S. pyogenes, but the number of resident tissue macrophages was significantly reduced in the aged host. Treatment of aged mice with macrophage colony-stimulating factor (M-CSF) significantly increased the number of resident macrophages and improved their response to infection. Our results indicate that treatment with M-CSF can restore, at least in part, the mechanisms affected by immunosenescence and enhance the natural resistance of aged mice to infection with S. pyogenes.
Immune recognition of Streptococcus pyogenes by dendritic cells.Streptococcus pyogenes is one of the most frequent human pathogens. Recent studies have identified dendritic cells (DCs) as important contributors to host defense against S. pyogenes. The objective of this study was to identify the receptors involved in immune recognition of S. pyogenes by DCs. To determine whether Toll-like receptors (TLRs) were involved in DC sensing of S. pyogenes, we evaluated the response of bone marrow-derived DCs obtained from mice deficient in MyD88, an adapter molecule used by almost all TLRs, following S. pyogenes stimulation. Despite the fact that MyD88(-/-) DCs did not differ from wild-type DCs in the ability to internalize and kill S. pyogenes, the up-regulation of maturation markers, such as CD40, CD80, and CD86, and the production of inflammatory cytokines, such as interleukin-12 (IL-12), IL-6, and tumor necrosis factor alpha, were dramatically impaired in S. pyogenes-stimulated MyD88(-/-) DCs. These results suggest that signaling through TLRs is the principal pathway by which DCs sense S. pyogenes and become activated. Surprisingly, DCs deficient in signaling through each of the TLRs reported as potential receptors for gram-positive cell components, such as TLR1, TLR2, TLR4, TLR9, and TLR2/6, were not impaired in the secretion of proinflammatory cytokines and the up-regulation of costimulatory molecules after S. pyogenes stimulation. In conclusion, our results exclude a major involvement of a single TLR or the heterodimer TLR2/6 in S. pyogenes sensing by DCs and argue for a multimodal recognition in which a combination of several different TLR-mediated signals is essential for a rapid and effective response to the pathogen.
Transcriptome analysis of murine macrophages in response to infection with Streptococcus pyogenes reveals an unusual activation program.The complex response of murine macrophages to infection with Streptococcus pyogenes was investigated at the level of gene expression with a high-density oligomer microarray. More than 400 genes were identified as being differentially regulated. Many of the up-regulated genes encode molecules involved in the immune response and in inflammation, transcription, signaling, apoptosis, the cell cycle, electron transport, and cell adhesion. Of particular interest was the up-regulation of proinflammatory cytokines, typical of the classically activated macrophages (M1 phenotype), such as tumor necrosis factor alpha, interleukin 1 (IL-1), and IL-6, and as well as the up-regulation of anti-inflammatory mediators, such as IL-1 decoy receptor and IL-10, associated with alternative macrophage activation (M2 phenotype). Furthermore, the gene encoding inducible nitric oxide synthase (iNOS), an enzyme typically implicated in classical activation, was not induced in infected macrophages. Instead, the gene encoding arginase, a competitor for the iNOS substrate arginine involved in the alternative activation pathway, was up-regulated in S. pyogenes-infected cells. Thus, the microarray-based gene expression analysis demonstrated that S. pyogenes induces an atypical activation program in macrophages, with some but not all features of the classical or alternative activation phenotypes. The microarray data also suggested that the bactericidal activity of macrophages against S. pyogenes is mediated by phagocyte oxidase, as p47phox was up-regulated in infected cells. Indeed, the in vivo and in vitro killing of S. pyogenes was markedly diminished in the absence of functional phagocyte (p47(phox-/-)) but not in the absence of iNOS (iNOS(-/-)). An understanding of how macrophages respond to S. pyogenes at the molecular level may facilitate the development of new therapeutic paradigms.