No abstract

IL-7 is vital for the development of the immune system and profoundly enhances the function of mature T cells. Chronic administration of IL-7 to mice markedly increases T cell numbers, especially CD8+ T cells, and enhances T cell functional potential. However, the mechanism by which these effects occur remains unclear. This report demonstrates that only 2 days of IL-7 treatment is needed for maximal enhancement of T cell function, as measured by proliferation, with a 6- to 12-fold increase in the proportion of CD4+ and CD8+ T cells in cell cycle by 18 h of ex vivo stimulation. Moreover, a 2-day administration of IL-7 in vivo increases basal proliferation by 4- and 14-fold in CD4+ and CD8+ T cells, respectively. These effects occur in the absence of cytokine production, increases in most activation markers, and changes in memory markers. This enhanced basal proliferation is the basis for the increase in T cell numbers in that IL-7 induces an additional 60% and 85% of resting CD4+ and CD8+ T cells, respectively, to enter cell cycle in mice given IL-7 for 7 days. These results demonstrate that in vivo administration of IL-7 increases T cell numbers and functional potential via a homeostatic, nonactivating process. These findings may suggest a unique clinical niche for IL-7 in that IL-7 therapy may increase T cell numbers and enhance responses to specific antigenic targets while avoiding a general, nonspecific activation of the T cell population.

To gain insights into the origin and genome evolution of the plague bacterium Yersinia pestis, we have sequenced the deep-rooted strain Angola, a virulent Pestoides isolate. Its ancient nature makes this atypical isolate of particular importance in understanding the evolution of plague pathogenicity. Its chromosome features a unique genetic make-up intermediate between modern Y. pestis isolates and its evolutionary ancestor, Y. pseudotuberculosis. Our genotypic and phenotypic analyses led us to conclude that Angola belongs to one of the most ancient Y. pestis lineages thus far sequenced. The mobilome carries the first reported chimeric plasmid combining the two species-specific virulence plasmids. Genomic findings were validated in virulence assays demonstrating that its pathogenic potential is distinct from modern Y. pestis isolates. Human infection with this particular isolate would not be diagnosed by the standard clinical tests, as Angola lacks the plasmid-borne capsule, and a possible emergence of this genotype raises major public health concerns. To assess the genomic plasticity in Y. pestis, we investigated the global gene reservoir and estimated the pangenome at 4,844 unique protein-coding genes. As shown by the genomic analysis of this evolutionary key isolate, we found that the genomic plasticity within Y. pestis clearly was not as limited as previously thought, which is strengthened by the detection of the largest number of isolate-specific single-nucleotide polymorphisms (SNPs) currently reported in the species. This study identified numerous novel genetic signatures, some of which seem to be intimately associated with plague virulence. These markers are valuable in the development of a robust typing system critical for forensic, diagnostic, and epidemiological studies.

Interaction of stem cell factor (SCF), a haematopoietic growth factor, with the receptor tyrosine kinase c-kit leads to autophosphorylation of c-kit as well as tyrosine phosphorylation of various substrates. Little is known about the role of the JAK/STAT pathway in signal transduction via receptor tyrosine kinases, although this pathway has been well characterized in cytokine receptor signal transduction. We recently found that the Janus kinase Jak2 associates with c-kit and that SCF induces rapid and transient phosphorylation of Jak2. Here we present evidence that SCF activates the transcription factor Stat1. Phosphorylated c-kit co-immunoprecipitates with Stat1 within 1 min of SCF stimulation of the human cell line MO7e. Co-precipitation experiments using glutathione S-transferase fusion proteins indicate that association with c-kit is mediated by the Stat1 SH2 domain. Stat1 is rapidly tyrosine-phosphorylated in response to SCF in MO7e cells, the murine cell line FDCP-1 and normal progenitor cells. SCF-induced phosphorylation of Jak2 and Stat1 was also observed in murine 3T3 fibroblasts stably transfected with full-length human c-kit receptor. Furthermore c-kit directly phosphorylates Stat1 fusion proteins in in vitro kinase assays. Electrophoretic mobility-shift assays with nuclear extracts from SCF-stimulated cell lines and normal progenitor cells indicate that activated Stat1 binds the m67 oligonucleotide, a high-affinity SIE promoter sequence. These results demonstrate that Stat1 is activated in response to SCF, and suggest that Stat1 is a component of the SCF signal-transduction pathway.

No abstract

Stem cell factor (SCF) is a hematopoietic growth factor that interacts with the receptor tyrosine kinase, c-kit. We have found that SCF- stimulates rapid and transient tyrosine phosphorylation of JAK2 in human and murine cell lines, as well as in normal human progenitor cells. JAK2 and c-kit were associated in unstimulated cells with further recruitment of JAK2 to the c-kit receptor complex after SCF stimulation. Treatment of cells with JAK2 antisense oligonucleotides resulted in a 46% decrease in SCF-induced proliferation. These data demonstrate that SCF induces tyrosine phosphorylation of JAK2 and suggest that JAK2 is a component of the SCF signal transduction pathway.

Recent work has demonstrated the importance of Janus family kinases (JAKs) and signal transducers and activators of transcription (STATs) in the stimulus-response coupling of receptors lacking intrinsic tyrosine kinase activity. In particular, the JAK-STAT pathway appears critical in signal transduction by interferon as well as numerous hematopoietic growth factors interacting with members of the hemapoietin receptor superfamily. Although ligands that interact with receptor tyrosine kinases (RTK), such as epidermal growth factor (EGF), platelet-derived growth factor (PDGF) and colony stimulating factor-1 (CSF-1), have been shown to induce increases in phosphorylation of both JAKs and STATs, little is known about activation of this pathway by stem cell factor (SCF). This review will summarize what is known about the JAK/STAT pathway in relation to SCF signal transduction.

Melioidosis is an emerging disease that is caused by the facultative intracellular pathogen Burkholderia pseudomallei. It is intrinsically resistant to many antibiotics and host risk factors play a major role in susceptibility to infection. Currently, there is no human or animal vaccine against melioidosis. In this study, multiple B. pseudomallei MSHR668 deletion mutants were evaluated as live attenuated vaccines in the sensitive BALB/c mouse model of melioidosis. The most efficacious vaccines after an intraperitoneal challenge with 50-fold over the 50% median lethal dose (MLD50) with B. pseudomallei K96243 were 668 ΔhisF and 668 ΔilvI. Both vaccines completely protected mice in the acute phase of infection and showed significant protection (50% survivors) during the chronic phase of infection. The spleens of the survivors that were examined were sterile. Splenocytes from mice vaccinated with 668 ΔhisF and 668 ΔilvI expressed higher amounts of IFN-γ after stimulation with B. pseudomallei antigens than splenocytes from mice vaccinated with less protective candidates. Finally, we demonstrate that 668 ΔhisF is nonlethal in immunocompromised NOD/SCID mice. Our results show that 668 ΔhisF and 668 ΔilvI provide protective cell-mediated immune responses in the acute phase of infection and promote long term survival in the sensitive BALB/c mouse model of melioidosis.