Nucleotide and amino acid sequences of oriT-traM-traJ-traY-traA-traL regions and mobilization of virulence plasmids of Salmonella enterica serovars enteritidis,gallinarum-pullorum,and typhimurium

The virulence plasmid of Salmonella enterica serovar Gallinarum-Pullorum (pSPV) but not those of Salmonella enterica serovars Enteritidis (pSEV) and Typhimurium (pSTV) can be readily mobilized by an F or F-like conjugative plasmid. To investigate the reason for the difference, the oriT-traM-traJ-traY-traA-traL regions of the three salmonella virulence plasmids (pSVs) were cloned and their nucleotide and deduced amino acid sequences were examined. The cloned fragments were generally mobilized more readily than the corresponding full-length pSVs, but the recombinant plasmid containing the oriT of pSPV was, as expected, more readily mobilized, with up to 100-fold higher frequency than the recombinant plasmids containing the oriT of the other two pSVs. The nucleotide sequences of the oriT-traM-traJ-traY-traA-traL region of pSEV and pSTV were almost identical (only 4 bp differences), but differed from that of pSPV. Major nucleotide sequence variations were found in traJ, traY, and the Tra protein binding sites sby and sbm. sby of pSPV showed higher similarity than that of pSEV or pSTV to that of the F plasmid. The reverse was true for sbm: similarity was higher with pSEV and pSTV than with pSPV. In the deduced amino acid sequences of the five Tra proteins, major differences were found in TraY: pSEV's TraY was 75 amino acids, pSTV's was 106 amino acids, and pSPV's was 133 amino acids; and there were duplicate consensus betaalphaalpha fragments in the TraY of pSPV and F plasmid, whereas there was only a single betaalphaalpha fragment in that of pSEV and pSTV.     

Production of granulocyte colony-stimulating factor in the nonspecific acute phase response enhances host resistance to bacterial infection

Mice mounting an acute phase response, induced by sterile inflammation after a single s.c. injection of casein 24 h beforehand, were remarkably protected against lethal infection with Gram-positive or Gram-negative bacteria. This was associated with enhanced early clearance of bacteremia, greater phagocytosis and oxidative burst responses by neutrophils, and enhanced recruitment of neutrophils into tissues compared with control, nonacute phase mice. Casein-induced inflammation was also associated with increased concentrations of G-CSF in serum, and administration of neutralizing Ab to this cytokine completely abrogated protection against Escherichia coli infection after casein pretreatment. Injection of recombinant murine G-CSF between 3 and 24 h before infection conferred the same protection as casein injection. In contrast, the casein-induced acute phase response affected neither serum values of TNF-alpha, IL-1 beta, or IL-6 after E. coli infection nor susceptibility to LPS toxicity. Furthermore, protection against infection was unaffected in IL-1R knockout mice, which have deficient acute phase plasma protein responses, or after nonspecific inhibition of acute phase protein synthesis by D-galactosamine or specific depletion of complement C3 by cobra venom factor. Increased production of G-CSF in the acute phase response is thus a key physiological component of host defense, and pretreatment with G-CSF to prevent bacterial infection in at-risk patients now merits further study, especially in view of increasing bacterial resistance to antibiotics.     

Donor T cell activation initiates small bowel allograft rejection through an IFN-gamma-inducible protein-10-dependent mechanism

The poor success in controlling small bowel (SB) allograft rejection is partially attributed to the unique immune environment in the donor intestine. We hypothesized that Ag-induced activation of donor-derived T cells contributes to the initiation of SB allograft rejection. To address the role of donor T cell activation in SB transplantation, SB grafts from DO11.10 TCR transgenic mice (BALB/c, H-2L(d+)) were transplanted into BALB/c (isografts), or single class I MHC-mismatched (L(d)-deficient) BALB/c H-2(dm2) (dm2, H-2L(d-)) mutant mice (allografts). Graft survival was followed after injection of control or antigenic OVA(323-339) peptide. Eighty percent of SB allografts developed severe rejection in mice treated with antigenic peptide, whereas <20% of allografts were rejected in mice treated with control peptide (p < 0.05). Isografts survived >30 days regardless of OVA(323-339) administration. Activation of donor T cells increased intragraft expression of proinflammatory cytokine (IFN-gamma) and CXC chemokine IFN-gamma-inducible protein-10 mRNA and enhanced activation and accumulation of host NK and T cells in SB allografts. Treatment of mice with neutralizing anti-IFN-gamma-inducible protein-10 mAb increased SB allograft survival in Ag-treated mice (67%; p < 0.05) and reduced accumulation of host T cells and NK cells in the lamina propria but not mesenteric lymph nodes. These results suggest that activation of donor T cells after SB allotransplantation induces production of a Th1-like profile of cytokines and CXC chemokines that enhance infiltration of host T cells and NK cells in SB allografts. Blocking this pathway may be of therapeutic value in controlling SB allograft rejection.     

Inhibitory effects of cytomegalovirus proteins US2 and US11 point to contributions from direct priming and cross-priming in induction of vaccinia virus-specific CD8(+) T cells

The extent to which naive CD8(+) CTLs (T(CD8)(+)) are primed by APCs presenting endogenous Ags (direct priming) or Ags acquired from other infected cells (cross-priming) is a critical topic in basic and applied immunology. To examine the contribution of direct priming in the induction of VV-specific T(CD8)(+), we generated recombinant vaccinia viruses that express human CMV proteins (US2 and US11) that induce the destruction of newly synthesized MHC class I molecules. Expression of US2 or US11 was associated with a 24-63% decrease in numbers of primary or secondary VV-specific T(CD8)(+) responding to i.p. infection. Using HPLC-isolated peptides from VV-infected cells, we show that US2 and US11 selectively inhibit T(CD8)(+) responses to a subset of immunogenic VV determinants. Moreover, VV-US2 and lysates from VV-infected histoincompatible cells elicit T(CD8)(+) specific for a similar subset of VV determinants. These findings indicate that US2 and US11 can function in vivo to interfere with the activation of virus-specific T(CD8)(+). Furthermore, they suggest that 1) both cross-priming and direct priming contribute significantly to the generation of VV-specific T(CD8)(+), 2) the sets of immunogenic vaccinia virus determinants generated by cross-priming and direct priming are not completely overlapping, and 3) cross-priming overrides the effects of cis-acting viral interference with the class I Ag presentation pathway.     

A lifetime perspective on foraging and mortality

Food intake carries many potential risks which may impair an animal's reproductive success not only in the current breeding cycle, but also for the rest of its lifetime. We examine the lifetime trade-off between the costs and benefits of food intake by presenting a simple animal foraging model, where each unit of food eaten carries with it a risk of mortality. We show that the optimal food intake rate over an animal's lifetime, for both semelparous and iteroparous animals, is not maximal. Instead, animals are required to strike a balance between the immediate reproductive benefits of gathering food and the future reproductive costs incurred by the food's mortality risk. This balance depends upon the lifespan of the animal as well as the nature of the risk. Different mortality risks are compared and it is shown that a mortality risk per unit time spent foraging is not, in general, equivalent to a mortality risk per unit of food consumed. The results suggest that a mortality risk per unit of food consumed, such as that presented by the presence of a toxin or of a parasite in the diet, has important consequences for feeding behaviour and is a possible factor involved in food intake regulation.     

Bi-trophic mathematical model for pest adaptation to a resistant crop

A version of the Lotka-Volterra predator-prey model with logistic crop growth is modified to explore the rate of adaptation of a herbivore to a pest-resistant crop. This provides a phenotypic model for the evolution of resistance in a population comprising three different pest types each defined by differing parameter values for respiration rate and crop palatability. Expressions estimating the rates of increase of the fitter pest types are obtained as a function of the food qualities, and respiration and mortality rates. Potential strategies for delaying the rate of adaptation with regard to the expressions derived above, via the use of pest-susceptible refugia and natural enemies, are discussed. Although the model is formulated as one in which a single gene is the factor conferring resistance it can be interpreted and used independently of this.     

Mice deficient in perforin,CD4+ T cells,or CD28-mediated signaling maintain the typical immunodominance hierarchies of CD8+ T-cell responses to influenza virus

CD8 T-cell (T(CD8+)) responses elicited by viral infection demonstrate the phenomenon of immunodominance: the numbers of T(CD8+) responding to different viral peptides vary over a wide range in a reproducible manner for individuals with the same major histocompatibility complex class I alleles. To better understand immunodominance, we examined T(CD8+) responses to multiple defined viral peptides following infection of mice with influenza virus. The immunodominance hierarchy of influenza virus-specific T(CD8+) was not greatly perturbed by the absence of either perforin or T-helper cells or by interference with B7 (CD80)-mediated signaling. These findings indicate that costimulation by antigen-presenting cells (APCs) or killing of APCs by T(CD8+) plays only a minor role in establishing the immunodominance hierarchy of antiviral T(CD8+) in this system. This points to intrinsic features of the T(CD8+) repertoire as major contributors to immunodominance.     

Coexistence and relative abundance in annual plant assemblages: the roles of competition and colonization

Although an interspecific trade-off between competitive and colonizing ability can permit multispecies coexistence, whether this mechanism controls the structure of natural systems remains unresolved. We used models to evaluate the hypothesized importance of this trade-off for explaining coexistence and relative abundance patterns in annual plant assemblages. In a nonspatial model, empirically derived competition-colonization trade-offs related to seed mass were insufficient to generate coexistence. This was unchanged by spatial structure or interspecific variation in the fraction of seeds dispersing globally. These results differ from those of the more generalized competition-colonization models because the latter assume completely asymmetric competition, an assumption that appears unrealistic considering existing data for annual systems. When, for heuristic purposes, completely asymmetric competition was incorporated into our models, unlimited coexistence was possible. However, in the resulting abundance patterns, the best competitors/poorest colonizers were the most abundant, the opposite of that observed in natural systems. By contrast, these natural patterns were produced by competition-colonization models where environmental heterogeneity permitted species coexistence. Thus, despite the failure of the simple competition-colonization trade-off to explain coexistence in annual plant systems, this trade-off may be essential to explaining relative abundance patterns when other processes permit coexistence.     

Ecological and genetic correlates of long-term population trends in the park grass experiment

The Park Grass Experiment (PGE) is the longest-observed set of experimental plant communities in existence. Although the gross composition of the vegetation was at equilibrium over the 60-yr period from 1920 to 1979, annual records show that individual species exhibited a range of dynamics. We tested two hypotheses to explain why some species initially increased and why subsequently some of these (the outbreak species) decreased again. The study was designed around eight phylogenetically independent contrasts (PICs), each containing related species with different dynamics. Our first hypothesis was that persistent increasers and outbreakers have higher intrinsic rates of natural increase than control species (species without trends), allowing them to spread when interspecific competition is reduced by drought. This was tested by measuring establishment and seed production of species in field experiments, with and without interspecific competition. Seed production in outbreak species responded more strongly to release from interspecific competition than it did in either of the other groups of species. Our second hypothesis was that outbreak species eventually declined because they lacked the genetic variation necessary to adapt to the novel habitats to which they had initially spread. We tested this by measuring mating systems and genetic diversity in persistent and outbreak species in the PGE. In seven out of seven PICs tested, the outbreak species was more selfing than its persistent relative. There was a significant positive correlation between outcrossing rate and gene diversity. These results support roles for both ecological and genetic traits in long-term dynamics.