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Chemical exchange saturation transfer (CEST) is a novel contrast mechanism for magnetic resonance imaging (MRl). CEST MRI selectively saturates exchangeable protons that are transferred to MRI-detectable bulk water signal. MRI-CEST (pH)-responsive agents are probes able to map pH in the microenvironment in which they distribute. To minimize the confounding effects of contrast agent concentration, researchers have developed ratiometric CEST imaging, which investigates contrast agents containing multiple magnetically non-equivalent proton groups, whose prototropic exchange have different pH responses. However, conventional ratiometric CEST MRI imposes stringent requirements on the selection of CEST contrasts agents. In this study, a novel ratiometric pH MRI method based on the analysis of CEST effects under different radio frequency irradiation power levels was developed. The proposed method has been demonstrated using iobitridol, an X-ray contrast agent analog of iopamidol but containing a single set of amide protons, both in vitro and in vivo. [ABSTRACT FROM AUTHOR]

Herpesvirus entry functions of the conserved glycoproteins gB and gH-gL have been delineated, but their role in regulating cell-cell fusion is poorly understood. Varicella-zoster virus (VZV) infection provides a valuable model for investigating cell-cell fusion because of the importance of this process for pathogenesis in human skin and sensory ganglia. The present study identifies a canonical immunoreceptor tyrosine-based inhibition motif (ITIM) in the gB cytoplasmic domain (gBcyt) and demonstrates that the gBcyt is a tyrosine kinase substrate. Orbitrap mass spectrometry confirmed that Y881, central to the ITIM, is phosphorylated. To determine whether the gBcyt ITIM regulates gB/gH-gL-induced cell-cell fusion in vitro, tyrosine residues Y881 and Y920 in the gBcyt were substituted with phenylalanine separately or together. Recombinant viruses with these substitutions were generated to establish their effects on syncytia formation in replication in vitro and in the human skin xenograft model of VZV pathogenesis. The Y881F substitution caused significantly increased cell-cell fusion despite reduced cell-surface gB. Importantly, the Y881 F or Y881 /920F substitutions in VZV caused aggressive syncytia formation, reducing cell-cell spread. These in vitro effects of aggressive syncytia formation translated to severely impaired skin infection in vivo. In contrast, the Y920F substitution did not affect virus replication in vitro or in vivo. These observations suggest that gB modulates cell-cell fusion via an ITIM-mediated Y881 phosphorylation-dependent mechanism, supporting a unique concept that intracellular signaling through this gBcyt motif regulates VZV syncytia formation and is essential for skin pathogenesis. [ABSTRACT FROM AUTHOR]

Background. The susceptibility of infants to infections is well defined clinically, and immunologic abnormalities have been described. Immune maturation is complex, however, and the interval during which changes occur during childhood has not been identified. Methods. To assess age-related differences in the CD4+ T cell responses, we evaluated the frequency of CD4+ T cells that produced interferon (IFN) γ in response to staphylococcal enterotoxin B (SEB) stimulation in 382 healthy infants and children (2 months to 11 years of age) and 66 adults. Flow cytometry was used to assess SEB-induced CD69 and CD40 ligand (CD40-L) expression and IFN-γ production by CD4+ and CD45RO+CD4+ T cells. Results. CD69 and CD40-L expression by CD4+ and CD45RO+CD4+ T cells were similar to adult levels from infancy, but the frequency of activated T cells that produced IFN-γ remained lower than adult responses until children were 10 years of age. Conclusions. These observations indicate that the IFN-γ response of CD4+ T cells to SEB remains limited for a much longer interval than was reported elsewhere, extending to the second decade of life. Observed differences in CD45RO+CD4+ T cell function indicate that CD4+ T cells with the same phenotypes do not possess equivalent functional capabilities. [ABSTRACT FROM AUTHOR]

Background: The susceptibility of infants to infections is well defined clinically, and immunologic abnormalities have been described. Immune maturation is complex, however, and the interval during which changes occur during childhood has not been identified., Methods: To assess age-related differences in the CD4(+) T cell responses, we evaluated the frequency of CD4(+) T cells that produced interferon (IFN) gamma in response to staphylococcal enterotoxin B (SEB) stimulation in 382 healthy infants and children (2 months to 11 years of age) and 66 adults. Flow cytometry was used to assess SEB-induced CD69 and CD40 ligand (CD40-L) expression and IFN-gamma production by CD4(+) and CD45RO(+)CD4(+) T cells., Results: CD69 and CD40-L expression by CD4(+) and CD45RO(+)CD4(+) T cells were similar to adult levels from infancy, but the frequency of activated T cells that produced IFN-gamma remained lower than adult responses until children were 10 years of age., Conclusions: These observations indicate that the IFN-gamma response of CD4(+) T cells to SEB remains limited for a much longer interval than was reported elsewhere, extending to the second decade of life. Observed differences in CD45RO(+)CD4(+) T cell function indicate that CD4(+) T cells with the same phenotypes do not possess equivalent functional capabilities.