Dendritic cells (DC) have been showed to both produce and respond to chemokines. To understand how this may impact on DC function, we analyzed the kinetics of chemokine production and responsiveness during DC maturation. After stimulation with LPS, TNF-alpha or CD40 ligand, the inflammatory chemokines MIP-1alpha, MIP-1beta and IL-8 were produced rapidly and at high levels, but only for a few hours, while RANTES and MCP-1 were produced in a sustained fashion. The constitutive chemokines TARC, MDC and PARC were expressed in immature DC and were up-regulated following maturation, while ELC was produced only at late time points. Activated macrophages produced a similar spectrum of chemokines, but did not produce TARC and ELC. In maturing DC chemokine production had different impact on chemokine receptor function. While CCR1 and CCR5 were down-regulated by endogenous or exogenous chemokines, CCR7 levels gradually increased in maturing DC and showed a striking resistance to ligand-induced down-regulation, explaining how DC can sustain the response to SLC and ELC throughout the maturation process. The time-ordered production of inflammatory and constitutive chemokines provides DC with the capacity to self-regulate their migratory behavior as well as to recruit other cells for the afferent and efferent limb of the immune response.

Macrophages and dendritic cells (DC) play an essential role in the initiation and maintenance of immune response to pathogens. To analyze early interactions between Mycobacterium tuberculosis (Mtb) and immune cells, human peripheral blood monocyte-derived macrophages (MDM) and monocyte-derived dendritic cells (MDDC) were infected with Mtb. Both cells were found to internalize the mycobacteria, resulting in the activation of MDM and maturation of MDDC as reflected by enhanced expression of several surface Ags. After Mtb infection, the proinflammatory cytokines TNF-α, IL-1, and IL-6 were secreted mainly by MDM. As regards the production of IFN-γ-inducing cytokines, IL-12 and IFN-α, was seen almost exclusively from infected MDDC, while IL-18 was secreted preferentially by macrophages. Moreover, Mtb-infected MDM also produce the immunosuppressive cytokine IL-10. Because IL-10 is a potent inhibitor of IL-12 synthesis from activated human mononuclear cells, we assessed the inhibitory potential of this cytokine using soluble IL-10R. Neutralization of IL-10 restored IL-12 secretion from Mtb-infected MDM. In line with these findings, supernatants from Mtb-infected MDDC induced IFN-γ production by T cells and enhanced IL-18R expression, whereas supernatants from MDM failed to do that. Neutralization of IFN-α, IL-12, and IL-18 activity in Mtb-infected MDDC supernatants by specific Abs suggested that IL-12 and, to a lesser extent, IFN-α and IL-18 play a significant role in enhancing IFN-γ synthesis by T cells. During Mtb infection, macrophages and DC may have different roles: macrophages secrete proinflammatory cytokines and induce granulomatous inflammatory response, whereas DC are primarily involved in inducing antimycobacterial T cell immune response.

Toll-like receptors (TLRs) mediate innate immune responses to microbes. TLR2, TLR5, TLR6, and TLR9 have been implicated in responses to bacterial components, and TLR4 is the receptor for Gram-negative bacteria. Recently, TLR4 was described to function in respiratory syncytial virus-induced NF-kappaB activation. Here we have analyzed TLR1-9 mRNA expression in human primary macrophages infected with influenza A and Sendai viruses. TLR1, TLR2, TLR4, TLR6, and TLR8 mRNAs were expressed at basal levels in macrophages. Viral infection enhanced TLR1, TLR2, TLR3, and TLR7 mRNA expression, and neutralizing anti-IFN-alpha/beta antibodies downregulated gene expression of these TLRs. Exogenously added IFN-alpha upregulated TLR1, TLR2, TLR3, and TLR7 mRNA expression in macrophages, as well as TLR3 mRNA expression in epithelial and endothelial cell lines. IFN-gamma enhanced the expression of TLR1 and TLR2 mRNA in macrophages, and TLR3 in epithelial and endothelial cells. The data suggests a novel role for IFNs in the activation of innate immunity.

The genus Yersinia has been used as a model system to study pathogen evolution. Using whole-genome sequencing of all Yersinia species, we delineate the gene complement of the whole genus and define patterns of virulence evolution. Multiple distinct ecological specializations appear to have split pathogenic strains from environmental, nonpathogenic lineages. This split demonstrates that contrary to hypotheses that all pathogenic Yersinia species share a recent common pathogenic ancestor, they have evolved independently but followed parallel evolutionary paths in acquiring the same virulence determinants as well as becoming progressively more limited metabolically. Shared virulence determinants are limited to the virulence plasmid pYV and the attachment invasion locus ail. These acquisitions, together with genomic variations in metabolic pathways, have resulted in the parallel emergence of related pathogens displaying an increasingly specialized lifestyle with a spectrum of virulence potential, an emerging theme in the evolution of other important human pathogens.genomics metabolic streamlining | pathoadaptation | Enterobacteriaceae B acterial species are defined on the basis of phenotypic characteristics, such as cellular morphology and biochemical characteristics, as well as DNA-DNA hybridization and 16S rRNA comparison. Using high-throughput whole-genome approaches we can now move beyond classic methods and develop population frameworks to reconstruct accurate inter-and intraspecies relationships and gain insights into the complex patterns of gene flux that define different taxonomic groups.Bacterial whole-genome sequencing has revealed enormous heterogeneity in gene content, even between members of the same species. From a bacterial perspective the acquisition of new genes provides the flexibility to adapt and exploit novel niches and opportunities. From a human perspective, integration of genes by bacteria has been directly linked to the emergence of new pathogenic clones, often from formerly harmless lineages (1, 2). In addition to gene gain, gene loss is also strongly associated with host restriction in acutely pathogenic bacterial species, such as Yersinia pestis and Salmonella enterica serovars, including Salmonella Typhi (3-5), where gene loss can remove functions unnecessary in the new niche (6). These specialist pathogens show a much higher frequency of functional gene loss than closely related host generalist pathogens, such as Yersinia pseudotuberculosis (7).Previous Yersinia genome studies (8, 9) have examined the evolution of pathogenicity by comparing strains from a selection of species or species subtypes within the genus, limiting our understanding of the evolutionary context of individual species. The majority of the Yersinia species are found in the environment and do not cause disease in mammals. Three species are known as human pathogens: the plague bacillus Y. pestis and the enteropathogens Yersinia enterocolitica and Y. pseudotuberculosis. SignificanceOur past understanding of pathogen evo...

Adherence of 3 persistent and 14 nonpersistent Listeria monocytogenes strains to stainless steel surfaces after short and long contact times was investigated. L. monocytogenes strains were obtained from poultry plants and an ice cream plant throughout several years. Adherence tests were performed in tryptic soy broth at 25 degrees C for 1, 2, and 72 h. Test surfaces were rinsed after the contact time, and attached cells were stained with acridine orange and enumerated with an epifluorescence microscope. The persistent poultry plant strains showed adherence 2- to 11-fold higher than the nonpersistent strains following 1- and 2-h contact times. The adherence of the persistent ice cream plant strain after 1- and 2-h contact times was higher than most of the nonpersistent strains. Seven of 12 nonpersistent ice cream strains showed an adherence of less than half that of the persistent strain. After 72 h, the differences in adherence were not as marked, since half the nonpersistent strains had reached adherence levels comparable with the persistent strains. In fact, three nonpersistent strains showed even higher adherence than the persistent strains. Thus, results of this study reveal that persistent L. monocytogenes strains show enhanced adherence at short contact times, promoting their survival in food processing facilities and possibly having an effect on initiation of persistent plant contamination.