Bacteremia caused by a recently described novel Desulfovibrio species.

An obligately anaerobic, fastidious, slowly growing, spiral, gram-negative bacterium was isolated from the blood of a 75-year-old man with acute onset of pyrexia. The patient responded rapidly to appropriate antibiotic therapy. Extensive investigation failed to detect a focus for the infection. Phenotypically, the organism was consistent with Desulfovibrio species. Microscopic investigation revealed an organism with a vibrioid or spirillioid morphology with rapidly progressive motility by means of a single polar flagellum. Biochemically, the organism produced large amounts of H2S and contained desulfovirdin. The 16S rRNA gene sequence of the organism was found to be most similar to those of members of the genus Desulfovibrio, with identical sequence homology to the newly proposed species described by Tee et al. (W. Tee, M. Dyall-Smith, W. Woods, and D. Eisen, J. Clin. Microbiol. 34:1760-1764, 1996). This is a second unrelated isolation of this novel species from two widely different locations in Australia. The two isolates show some phenotypic differences, indicating that they are different strains of the same species.     

Monoclonal antibodies against a rat leucocyte antigen block antigen-induced T-cell responses via an effect on accessory cells.

The MRC OX-45 and OX-46 mouse monoclonal antibodies recognize a rat cell surface glycoprotein of 45,000 MW that is present on a wide variety of haematopoietic cells and on endothelial cells. MRC OX-45 IgG or F(ab')2 blocked the primary mixed lymphocyte response (MLR) and the secondary response of T lymphocytes to the soluble antigen DNP-BGG. In contrast, the antibodies had no effect on the cytotoxic activity of specific (CTL) or non-specific (NK) killer cells or on proliferative responses stimulated by lectins or oxidative mitogenesis. The inhibitory effect was at the level of stimulator cells rather than responders since mouse anti-rat xenogeneic MLRs were inhibited but rat anti-mouse responses were unaffected. However, the effect was not a direct one because inhibition was seen when irradiated spleen cells were used as stimulators but not when cell populations highly enriched for dendritic cells were used. In the latter case, inhibition potentiated by antibody could be restored if a peritoneal cell population enriched for macrophages was added back to the cultures. The inhibitory effects of these monoclonal antibodies seem most likely to be due to potentiation of nonspecific suppression by macrophages.     

Correction of radioresistant DNA synthesis in ataxia telangiectasia fibroblasts by prostaglandin E2 treatment.

Cultured cells from patients inheriting the rare cancer-prone and radiotherapy-sensitive disorder ataxia telangiectasia (AT) exhibit defects in the activation of cell-cycle checkpoints after exposure to ionizing radiation. In particular, the failure of AT cells to arrest transiently the DNA de novo replication machinery immediately after irradiation--so-called radioresistant DNA synthesis (RDS)--is often taken as a molecular hallmark of the disease. Recently we reported that: (i) the radiation-responsive S-phase checkpoint operating in normal human cells is mediated by a signal transduction pathway involving Ca2+/calmodulin-dependent protein kinase II (CaMKII); and (ii) the RDS phenotype of AT cells is associated with failure to mobilize Ca2+ from intracellular stores, which is required for activation of the CaMKII-dependent S-phase arrest. In the present study, we demonstrate that the RDS phenotype of AT dermal fibroblasts can be rectified in the absence of ectopic expression of functional ATM, the 350-kDa protein kinase encoded by the gene mutated in AT. Correction of RDS was observed when AT fibroblasts were coincubated with normal fibroblasts under conditions in which the 2 different cell cultures shared the same medium but were completely separated physically. The RDS trait was also rectified when AT fibroblasts were briefly incubated with prostaglandin E2 in the absence of normal feeder cells, signifying that this ubiquitous eicosanoid can serve as the diffusible "RDS-correction factor" for AT cells in the aforementioned cocultivation studies. It would therefore appear that prostaglandin E2 can assume the role of an extracellular signaling modulator of the S-phase checkpoint in AT cells exposed to ionizing radiation, inducing DNA synthesis shutdown via an alternative, ATM-independent signal transduction pathway.     

The off-transient pulmonary oxygen uptake (VO(2)) kinetics following attainment of a particular VO(2) during heavy-intensity exercise in humans

The oxygen uptake response to moderate-intensity exercise (i.e. < anaerobic threshold (an)) has been characterised with a gain (i.e. response amplitude per increment of work rate) and time constant that do not vary appreciably at different work rates or between the on- and off-transients. Above an, the response becomes more complex with an early component that typically projects to a value that has a gain similar to that of the < an response, but which is supplemented by the addition of a delayed slow kinetic component. We therefore established a constant target VO2 (VO21) for each subject such that with different imposed work rates the contribution to VO21 from the slow phase varied over a wide range. Work rates were chosen so that VO21 was attained at 2-24 min. Five subjects (aged 21-58 years) cycled at four to five different work rates. VO2 was measured breath-by-breath, at VO21 the work rate was abruptly reduced and the subject recovered by cycling unloaded for 15 min. Unlike the on-transient, for which the slow component shows a long delay, the off-transient was best fitted as two simultaneous exponential components. The slower off-transient component had a small amplitude and long time constant, but did not differ significantly among the various tests. The off-transient kinetics for VO2 therefore was independent of the magnitude of the contribution to the slow phase from the on-transient kinetics.     

Age of diagnosis-based linkage analysis in type 1 diabetes

Genetic linkage studies of type 1 diabetes have produced a number of conflicting results, suggesting a high degree of locus heterogeneity in this disease. Approaches which model such heterogeneity will increase the power to fine map susceptibility loci. Here, using data from a genome scan of 356 affected sib pairs with type 1 diabetes, we performed heterogeneity analysis based on similarity of age at diagnosis of the sib pairs. We observed linkage to the region on chromosome 4p16.3 in sib pairs both diagnosed over the age of 10 years, whilst there was no evidence for linkage in sib pairs diagnosed before age 10 years. In contrast the sib pairs diagnosed before the age of 10 years demonstrated linkage to IDDM10, on chromosome 10p. Age of diagnosis-based heterogeneity analyses in complex diseases may be particularly helpful in mapping some susceptibility loci.     

Sex of affected sibpairs and genetic linkage to type 1 diabetes

A mouse model of diabetes shows gender dimorphism in the cumulative incidence of diabetes. Based on this, evidence for genetic linkage to IDDM13 on chromosome arm 2q was reported to be greater in type 1 diabetes families where there was a predominance of affected female offspring compared with families with a predominance of affected male offspring. Our objective was to investigate whether the sex of affected offspring affects evidence for linkage to susceptibility loci. Data from a genome scan of 356 affected sibpair families with type 1 diabetes were analysed to determine if there is differential evidence for linkage in families with affected children of a particular sex. At markers on chromosomes 3, 5, 7, 9, 11, and 19, we found a number of regions where the evidence for linkage is greater in families with affected sibpairs of a particular sex. Thus, evidence for linkage in families with affected sibpairs of the same gender suggests the presence of additional susceptibility loci. Several biological explanations are possible for these findings, including X and Y linkage, effects of sex hormones on gene expression, and quasi-linkage between sex chromosomes and autosomes.     

The self antigen heme evades immune recognition by sequestration in some hemoproteins

Heme is a non-protein autoantigen which is ubiquitous in vivo, primarily complexed in various hemoproteins or bound to specialized carrier molecules. Nevertheless, heme is able to stimulate a high frequency of CD4⁺, class II-restricted T cells, freshly explanted from unprimed mice, to proliferate in vitro. In this study, we show that heme incorporated into various species of mammalian cytochrome c (cyt c), including murine cyt c, represents a facultative cryptic determinant, able to be recalled only at high doses of native cyt c. By contrast, avian cyt c is of comparable antigenicity to free heme. Artificially denatured carboxymethylated (CM) mammalian cyt c exhibited greatly increased antigenicity, comparable to that of heme and avian cyt c, indicating that the crypticity of heme in native mammalian cyt c is due to the resistance of the native conformation of this molecule to antigen processing within murine antigen-presenting cells. Thus, tolerance to the heme group of at least some hemoproteins, may be maintained by the crypticity of the heme, rather than by deletion of hemereactive T cells. Given the high frequency of heme-reactive T cells in unprimed mice, these findings suggest that heme may become an important modulator during an inflammatory response.     

The autoantigenic response to rabbit cytochrome c

In this report we describe the production and characterization of autoantibody responses to rabbit cytochrome c (cyt c) in rabbits immunized with either the native monomeric or polymerized form of rabbit cyt c. Fine-specificity analyses of the response indicated that the majority of the response was to the evolutionarily conserved amino-terminal region of the molecule. The relative affinity of the autoantibody interaction with rabbit cyt c was assessed by a solid-phase assay and was found to be lower than that observed for rabbit anti-horse cyt c antibody populations. These findings are consistent with the prediction that low-affinity self-reactive B cells may escape tolerance induction.     

Analysis and gene assignment of mRNAs of a paramyxovirus, simian virus 5

Polypeptides synthesized by the paramyxovirus SV5 in infected CV-1 cells were readily identified when the host cell was treated with actinomycin D. The unglycosylated forms of HN and Fo synthesized in infected cells in the presence of tunicamycin and HN and Fo synthesized in vitro were identified by immunoprecipitation with specific antibodies. Separation of SV5-specific poly(A)-containing RNAs on methyl-mercury agarose gels and in vitro translation of fractions, indicated that the viral polypeptides were translated from individual mRNAs except P (Mr approximately 44K) and the nonstructural polypeptide V (Mr approximately 24K) for which the mRNAs could not be separated. cDNA copies of SV5-specific mRNAs were synthesized and cloned in plasmid pBR322. Clones to NP, P + V, M, F, and HN were identified by hybrid-arrest and hybrid-selection translation of SV5 mRNAs. Tryptic peptide mapping of polypeptides P and V indicated that the peptides of V were a subset of those of P. Hybridization of cDNA probes to infected cell mRNAs separated on agarose gels permitted identification of the NP, P + V, M, F, and HN mRNAs and presumptive polycistronic mRNAs. The sizes and sequence homologies of these polycistronic mRNAs were used to derive a likely gene order on the SV5 50 S genome RNA.