13 research outputs found

    Detailed Kinetics of the Direct Allo-Response in Human Liver Transplant Recipients: New Insights from an Optimized Assay

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    Conventional assays for quantification of allo-reactive T-cell precursor frequencies (PF) are relatively insensitive. We present a robust assay for quantification of PF of T-cells with direct donor-specificity, and establish the kinetics of circulating donor-specific T cells after liver transplantation (LTx). B cells from donor splenocytes were differentiated into professional antigen-presenting cells by CD40-engagement (CD40-B cells). CFSE-labelled PBMC from LTx-recipients obtained before and at several time points after LTx, were stimulated with donor-derived or 3rd party CD40-B cells. PF of donor-specific T cells were calculated from CFSE-dilution patterns, and intracellular IFN-γ was determined after re-stimulation with CD40-B cells. Compared to splenocytes, stimulations with CD40-B cells resulted in 3 to 5-fold higher responding T-cell PF. Memory and naïve T-cell subsets responded equally to allogeneic CD40-B cell stimulation. Donor-specific CD4+ and CD8+ T-cell PF ranged from 0.5 to 19% (median: 5.2%). One week after LTx, PF of circulating donor-specific CD4+ and CD8+ T cells increased significantly, while only a minor increase in numbers of T cells reacting to 3rd party allo-antigens was observed. One year after LTx numbers of CD4+ and CD8+ T cells reacting to donor antigens, as well as those reacting to 3rd party allo-antigens, were slightly lower compared to pre-transplant values. Moreover, CD4+ and CD8+ T cells responding to donor-derived, as well as those reacting to 3rd party CD40-B cells, produced less IFN-γ. In conclusion, our alternative approach enables detection of allo-reactive human T cells at high frequencies, and after application we conclude that donor-specific T-cell PF increase immediately after LTx. However, no evidence for a specific loss of circulating T-cells recognizing donor allo-antigens via the direct pathway up to 1 year after LTx was obtained, underscoring the relative insensitiveness of previous assays

    Contribution of stored pre-anthesis assimilate to grain yield in wheat and barley

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    Reserves of assimilate present in wheat and barley crops a flowering, and available for later translocation to the grains could buffer grain yield against environmental stresses durin; grain filling. This so-called pre-anthesis assimilate contributioi to grain yield can be expressed as a percentage of yield (Pj Archbold1, and later Thome2, concluded. that Px was small being no more than 20%2. But only one result (12 % for irrigate! wheat at Cambridge3) refers to a crop in the field as distinc from plants in pots, and no studies considered the effect o stress during grain filling. Recently Gallagher et a/.4,B reports substantial contributions: Px averaged 43% over six crops o wheat and barley at Nottingham; this amounted to more thai 300 g per ms of dry material in two crops and, in the sever drought of 1970, 39% of total dry matter present at anthesis They assumed, with some supporting evidence from one bade; crop8, that the pre-anthesis contribution was given by th decrease from anthesis to maturity in dry weight of non-graii parts of the crop. In situ labelling with 14C02 of the whole croj canopy at frequent intervals before and after anthesis woul« seem to be the least equivocal way of estimating Px. Using thi method we have determined i\ in wheat and barley. It averagei only 12% (watered crops) and 22% (draughted crops), and di* not agree with estimates for the same crops obtained by th method of Gallagher et a/.**6

    Die Fruchtbildung

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    Wnt Signaling and the Control of Human Stem Cell Fate

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