Attenuated mutants of Staphylococcus aureus with two temperature-sensitive lesions: isolation and characterization

The feasibility of constructing attenuated mutants of Staphylococcus aureus with two temperature-sensitive (ts) lesions for ultimate development of a live-attenuated strain was investigated. Temperature-sensitive S. aureus strain G/1/2, which grows well at 31 degrees C but does not replicate at 37 degrees C, was subjected to chemical mutagenesis. After two enrichment cycles, fifteen mutants able to grow at 25 degrees C but unable to grow at 31 degrees C, were identified. Growth curves with temperature shifts from 25 to 31 degrees C, and from 31 to 37 degrees C confirmed that these were mutants with two lesions (dts), each with a different cut-off temperature. The reversion frequency of mutant G/1/2 at 37 degrees C was 2 x 10(-6) whereas those of several dts mutants were much lower (dts7: 7 x 10(-9) and dts12: 1 x 10(-9)). There was no increase in ts mutation reversion rate in response to prolonged incubation at 37 degrees C. The data support the further development of these mutants for use as a stable attenuated vaccine.     

Taxonomy of the musk deer (Artiodactyla, Mammalia)

The autosomal recessive disorder xeroderma pigmentosum (XP) results from defects in the nucleotide excision repair (NER) pathway for DNA repair. NER normally repairs bulky DNA lesions, such as pyrimidine dimers resulting from UV radiation. XP patients have high rates of skin cancer, and some also develop progressive neurological degeneration. To better understand the mechanism of this neurodegeneration, I used a specific assay for the multicomponent excision nuclease of the NER pathway in cell-free extracts from the adult rat brain. Excision nuclease activity was detectable in whole-cell extracts prepared from the cerebellum, whereas extracts prepared from the forebrain, which has a lower density of cell nuclei, had much less activity. Nuclear extracts from both areas were equally capable of restoring activity to extracts from two different NER-deficient cell lines, despite large differences in the ratio of neurons to nonneuronal cells in the cerebellum and forebrain. These results indicate that the NER pathway is functional in neuronal cells in the adult brain. The implications of this finding for XP and other neurodegenerative diseases is discussed.     

Respiratory syncytial virus infection of human respiratory epithelial cells up-regulates class I MHC expression through the induction of IFN-beta and IL-1 alpha

CD8+ T cells mediate some of the damage to the lung epithelium following respiratory syncytial virus (RSV) infection. Since CD8+ T cells recognize antigen-laden class I MHC molecules on the target cells, we examined in this study the expression of class I MHC by RSV-infected respiratory epithelial cells. Respiratory epithelial cell lines and bronchial epithelial cells from normal human tissue responded to RSV infection with an increased expression of class I MHC as determined by flow cytometry and immunoprecipitation of class I MHC from metabolically radiolabeled cells. The increase in class I MHC expression was dependent on infectious, replicating virus. UV-irradiated culture supernatants from RSV-infected A549 cells, when added to fresh A549 cell cultures, induced an increase in class I MHC expression by those cells. The class I MHC increasing activity within supernatants from A549 cells was due, in large part, to IFN-beta, and to a lesser extent to IL-1 alpha. The addition of neutralizing Abs to both cytokines completely blocked the increase in class I MHC expression by cells treated with the above-mentioned supernatants. These results demonstrate that RSV infection elicits IFN-beta production by respiratory epithelial cells, which in turn leads to an increase in their synthesis of class I MHC, which would facilitate their recognition and lysis by RSV-specific CD8+ T cells.