Cytokine cascade in sepsis

Sepsis is associated with an exacerbated production of both pro- and anti-inflammatory cytokines, which are detectable within the bloodstream. Their 'half-angel, half-devil' properties are fully illustrated in sepsis. While they are a prerequisite to fight infection, their overzealous production is deleterious. The highest levels are found in plasma of non-surviving patients: they are markers and causative agents of poor outcome. Only the level of the chemokine RANTES is inversely associated with the APACHE II score (r = -0.7; p = 0.02) and low levels are associated with poor outcome. The link, interplay and network of cytokines taking place during sepsis are illustrated by the correlations between the levels of most pro- and anti-inflammatory cytokines. Excessive release of anti-inflammatory cytokines may be associated with the immunodysregulation observed in sepsis. However, despite the presence of huge amounts of anti-inflammatory cytokines and molecules targeting specifically interleukin-1 (IL-1) (i.e. IL-1 receptor antagonist) and tumour necrosis factor (TNF) (i.e. soluble TNF receptors), there is no indication that their levels are sufficient to counteract fully these proinflammatory cytokines. TNF was initially thought to be the 'hub of the cytokine network'. Although TNF contributes towards favouring the production of many other cytokines within a complex cascade, there are numerous examples to illustrate that its presence is not a prerequisite for these productions.     

Herpes simplex virus type 1-induced FasL expression in human monocytic cells and its implications for cell death, viral replication, and immune evasion

Herpes simplex virus type 1 (HSV-1) is a ubiquitously occurring pathogen that infects humans early in childhood. The virus persists as a latent infection in dorsal root ganglia, especially of the trigeminal nerve, and frequently becomes reactivated in humans under conditions of stress. Monocytic cells constitute an important component of the innate and adaptive immune responses. We show here for the first time that HSV-1 stimulates human FasL promoter and induces de novo expression of FasL on the surface of human monocytic cells, including monocytes and macrophages. This virus-induced FasL expression causes death of monocytic cells growing in suspension, but not in monolayers (e.g., macrophages). The addition of a broad-spectrum caspase inhibitor, as well as anti-FasL antibodies, reduced cell death but increased viral replication in the virus-infected cell cultures. We also show here for the first time that the virus-induced de novo expression of FasL on the cell surface acts as an immune evasion mechanism by causing the death of interacting human CD4+ T cells, CD8+ T cells, and natural killer (NK) cells. Our study provides novel insights on FasL expression and cell death in HSV-infected human monocytic cells and their impact on interacting immune cells.     

Unusual composition of a yeast chromosome arm is associated with its delayed replication

The 11.3-Mb genome of the yeast Lachancea (Saccharomyces) kluyveri displays an intriguing compositional heterogeneity: a region of ∼1 Mb, covering almost the whole left arm of chromosome C (C-left), has an average GC content of 52.9%, which is significantly higher than the 40.4% global GC content of the rest of the genome. This region contains the MAT locus, which remains normal in composition. The excess of GC base pairs affects both coding and noncoding sequences, and thus is not due to selective pressure acting on protein sequences. It leads to a strong codon usage bias and alters the amino acid composition of the 457 proteins encoded on C-left that do not show obvious bias for functional categories, or the presence of paralogs or orthologs of essential genes of Saccharomyces cerevisiae. They share significant synteny conservation with other species of the Saccharomycetaceae, and phylogenetic analysis indicates that C-left originates from a Lachancea species. In contrast, there is a complete absence of transposable elements in C-left, whereas 18 elements per megabase are distributed across the rest of the genome. Comparative hybridization of synchronized cells using high-density genome arrays reveals that C-left is replicated later during S phase than the rest of the genome. Two possible primary causes of this major compositional heterogeneity are discussed: an ancient hybridization of two related species with very distinct GC composition, or an intrinsic mechanism, possibly associated with the loss of the silent cassettes from C-left that progressively increased the GC content and generated the delayed replication of this chromosomal arm.Lachancea kluyveri is a budding yeast first isolated from the intestinal canal of Drosophila in the Yosemite region of California, described as Saccharomyces kluyveri in 1956 (Phaff et al. 1956), and reclassified in the Lachancea genus (Kurtzman 2003), an assignment confirmed by additional phylogenetic studies (Wu et al. 2008). The Lachancea clade includes L. thermotolerans and L. waltii (formerly classified in the Kluyveromyces) and L. cidri, L. fermentati (formerly classified in the Zygosaccharomyces), and L. meyersii (Naumova et al. 2007). L. kluyveri has been isolated from the Drosophila species in North America, from soil in Europe, and from various tree species in India and North America.In contrast to S. cerevisiae, L. kluyveri ferments sugars only in the absence of oxygen, and its efficient use of glucose makes it a valuable organism for industrial protein production under aerobic glucose-limited conditions (Møller et al. 2004). Unlike most Saccharomycetaceae, L. kluyveri can use pyrimidines and their degradation products as its sole nitrogen source (Gojkovic et al. 2003).The type strain of the species (CBS 3082) is diploid, and like all Lachancea species has eight chromosomes (Weinstock and Strathern 1993; Neuvéglise et al. 2000; Naumova et al. 2007). There have been two preliminary surveys of its genome (Neuvéglise et al. 2000; Cliften et al. 2001, 2003), and it has now been fully sequenced and annotated (The Génolevures Consortium 2009). The 11.3-Mb nuclear genome contains 5321 predicted protein-encoding genes and 257 tRNA genes; it is ∼900 kb larger than that of L. thermotolerans with about 300 more genes. The genome contains few transposable elements, with only one family of degenerate class II elements and two families of long-terminal repeat (LTR) retrotransposons. The major family, the Ty1/copia element Tsk1, contains potential active elements that might have been acquired by horizontal transfer (Neuvéglise et al. 2002).The most intriguing feature of L. kluyveri is the high GC content (52.9%) of the 1-Mb left arm of chromosome C (abbreviated here as “C-left”). The rest of the genome is a homogeneous 40.4% GC (The Génolevures Consortium 2009). The genomes of two related Lachancea, L. thermotolerans (The Génolevures Consortium 2009) and L. waltii (Kellis et al. 2004), do not show large-scale compositional heterogeneity. This is also true for all other yeasts, where GC content variations are limited to local differences between intergenic regions (lower GC content), protein-coding sequences (higher GC content), and genes for noncoding RNAs (highest GC content). For filamentous fungi, large-scale compositional heterogeneity has been reported for the phytopathogen Leptosphaeria maculans, whose genome displays an isochore-like structure (Gout et al. 2006; Fudal et al. 2007). Some of its chromosomes consist of mosaics of GC-rich fragments (51% GC) and AT-rich segments (35% GC) of up to 453 kb that are almost devoid of genes. These AT-rich regions include a few avirulence genes embedded in stretches of highly degenerated LTR retrotransposons due to extensive repeat-induced point mutations. The green algae species Ostreococcus also exhibit significant GC content heterogeneity (Derelle et al. 2006; Palenik et al. 2007). In these species, two chromosomes have a much lower GC content than the rest of the genome, reaching 13% in O. lucimarinus. In these chromosomes, the bias in gene function, intron-containing genes, and transposable element content is associated with a dramatic increase of intrachromosomal rearrangement. Whereas one chromosome is suspected to have been acquired by horizontal transfer, the other one is proposed to be a sex-determining chromosome. The genomes of mammals and other vertebrates have long been known to be mosaics of isochores of GC-rich and GC-poor regions longer than 300 kb (Macaya et al. 1976), correlated with strong biases in gene density or repeated sequences, and with some biases in gene expression, replication timing, and recombination (Bernardi 2007). In the above examples, the GC-content heterogeneity is explained by specific chromosomal organization or genetic content. Here, we describe the unusual characteristics of L. kluyveri C-left, and we present two alternative hypotheses to account for its origin: a unique chromosomal arm exchange versus a progressive GC-content elevation related to delayed DNA replication.     

Are Hormonal Responses to Exercise in Young Men with Down’s Syndrome Related to Reduced Endurance Performance?

The aim of the present study was to analyse whether hormonal responses could explain an exercise limitation in Down's syndrome (DS). Fourteen young men with DS (mean age 22.5 ± 0.7 years) and 15 controls (CONT, mean age 22.5 ± 0.3 years) participated in the study. During a treadmill submaximal incremental test, blood samples were collected for determination of hormonal and metabolic variables. Compared to CONT, DS individuals showed lower VO_2max (P < 0.05), and lower duration of submaximal incremental exercise (P < 0.001). At rest, DS individuals showed greater catecholamines, insulin and leptin values (P < 0.05), but lower testosteronemia and cortisolemia (P < 0.05), compared to CONT. During submaximal incremental tests, catecholamines and cortisol were not increased, whereas the insulin concentration of DS individuals was significantly higher (P < 0.01) compared to CONT. Glycaemia increased significantly at the end of submaximal incremental test for CONT but not for DS individuals (P < 0.01). Maximal fat oxidation was lower (P < 0.01), whereas non-esterified fatty acids concentrations rose significantly during submaximal exercise in DS individuals. These results indicate an altered hormonal response to exercise in DS individuals. This endocrine profile at rest and during exercise may limit endurance performance in DS individuals.     

Systemic and hepatosplanchnic macro- and microcirculatory dose response to arginine vasopressin in endotoxic rabbits

OBJECTIVE: Arginine vasopressin (AVP) is being used increasingly to treat vasodilatory hypotension, although its effects on hepatosplanchnic perfusion have been debated. DESIGN: Prospective study in a university-based experimental research laboratory. SUBJECTS AND INTERVENTIONS: We compared the effect of AVP on systemic, gut, and liver blood flow in anesthetized and ventilated rabbits given either saline or endotoxin. Incremental i.v. boluses of AVP ranging from 1 to 1,000[Symbol: see text]ng were administered 90[Symbol: see text]min post-endotoxin or saline. MEASUREMENTS AND RESULTS: Endotoxin induced a shock state with a transient decrease of mesenteric artery blood flow velocity (pulsed Doppler, in centimeters per second, V(mes)) but had no effect on liver surface microcirculation (laser Doppler in TPU, MicroFl(liver)). Gut microcirculatory (MicroFl(gut)) changes became independent of mean arterial pressure (MAP) after endotoxin. In control rabbits (n = 5), increasing doses of AVP elevated MAP but reduced aortic blood flow (pulsed Doppler, VAo), V(mes), and MicroFl(gut) (p < 0.05). In endotoxic animals (n = 6), AVP produced a similar rise in MAP (p < 0.05), while V(mes) and MicroFl(gut) only decreased for AVP doses above 100[Symbol: see text]ng (p < 0.05). Liver microcirculation was only minimally affected by AVP, although significantly, both in control and endotoxin animals. CONCLUSION: Preservation of mesenteric blood flow as well as gut and liver microcirculation, with therapeutic doses of AVP during endotoxemia, supports its use as a hemodynamic agent during septic shock.