The missing M dwarfs

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The effect of cyclosporin on major histocompatibility complex-linked resistance to murine cytomegalovirus

The ability of mice to survive infection with murine cytomegalovirus (MCMV) is known to be influenced by genes of the major histocompatibility complex (MHC). One hypothesis to account for this association is that MHC-linked resistance to MCMV is an ‘immune response’ gene effect, caused by differences in the strength of the MHC-restricted T cell response of mouse strains with different MHC haplotypes. Therefore, removal of T cell responses in mouse strains differing only at the MHC should render them equally susceptible to the virus infection. To test this hypothesis, the immunosuppressive drug cyclosporin (CsA) was used to reduce T cell responses in inbred congenic mouse strains carrying either a resistant or susceptible MHC haplotype. CsA reduced the delayed-type hypersensitivity (DTH) response to MCMV in both resistant and susceptible mouse strains to background levels, equivalent to control uninfected mice. CsA treatment had little effect on the susceptibility of C57BL/10 and B10.BR mice to the virus and the differences in susceptibility between these strains remained. In contrast, CsA increased the susceptibility of the genetically susceptible BALB/c mice (H-2d) by 100-fold and increased the susceptibility of resistant BALB.K mice (H-2k) by 15-fold. Thus the H-2-determined difference in susceptibility between these strains was increased after CsA treatment. The results obtained with congenic strains show that MHC-linked resistance patterns to MCMV are not eliminated by CsA and suggest therefore that T cells are not responsible for this phenomenon. Interestingly, the mean time to death was delayed for CsA-treated BALB/c mice compared with untreated mice given equivalent virus doses. In addition, although CsA prevented DTH responses in both genetically susceptible A/J (H-2a) and resistant CBA (H-2k) mice, CsA treatment markedly increased the susceptibility of A/J mice (32-fold) but had little effect on the susceptibility of CBA mice to the virus

Estimating Lymphocyte Division and Death Rates from CFSE Data

The division tracking dye, carboxyfluorescin diacetate succinimidyl ester (CFSE) is currently the most informative labeling technique for characterizing the division history of cells in the immune system. Gett and Hodgkin [Nat. Immunol. 1:239–244, 2000] have pioneered the quantitative analysis of CFSE data. We confirm and extend their data analysis approach using simple mathematical models. We employ the extended Gett and Hodgkin [Nat. Immunol. 1:239–244, 2000] method to estimate the time to first division, the fraction of cells recruited into division, the cell cycle time, and the average death rate from CFSE data on T cells stimulated under different concentrations of IL-2. The same data is also fitted with a simple mathematical model that we derived by reformulating the numerical model of Deenick et al. [J. Immunol. 170:4963–4972, 2003]. By a non-linear fitting procedure we estimate parameter values and confidence intervals to identify the parameters that are influenced by the IL-2 concentration. We obtain a significantly better fit to the data when we assume that the T cell death rate depends on the number of divisions cells have completed. We provide an outlook on future work that involves extending the Deenick et al. [J. Immunol. 170:4963– 4972, 2003] model into the classical Smith–Martin model, and into a model with arbitrary probability distributions for death and division through subsequent divisions

Pre-mitotic genome re-organisation bookends the B cell differentiation process

During cellular differentiation chromosome conformation is intricately remodelled to support the lineage-specific transcriptional programs required for initiating and maintaining lineage identity. When these changes occur in relation to cell cycle, division and time in response to cellular activation and differentiation signals has yet to be explored, although it has been proposed to occur during DNA synthesis or after mitosis. Here, we elucidate the chromosome conformational changes in B lymphocytes as they differentiate and expand from a naive, quiescent state into antibody secreting plasma cells. We find gene-regulatory chromosome reorganization in late G1 phase before the first division, and that this configuration is remarkably stable as the cells massively and rapidly clonally expand. A second wave of conformational change occurs as cells terminally differentiate into plasma cells, coincident with increased time in G1 phase. These results provide further explanation for how lymphocyte fate is imprinted prior to the first division. They also suggest that chromosome reconfiguration occurs prior to DNA replication and mitosis, and is linked to a gene expression program that controls the differentiation process required for the generation of immunity.Wing Fuk Chan, Hannah D. Coughlan, Jie H. S. Zhou, Christine R. Keenan, Naiara G. Bediaga, Philip D. Hodgkin, Gordon K. Smyth, Timothy M. Johanson, Rhys S. Alla

Eight new T4.5-T7.5 dwarfs discovered in the UKIDSS large area survey data release 1

The definitive version is available at www.blackwell-synergy.com Copyright Blackwell Publishing DOI : 10.1111/j.1365-2966.2007.12023.xPeer reviewe