Reviewing research priorities in weed ecology, evolution and management: a horizon scan.

Weedy plants pose a major threat to food security, biodiversity, ecosystem services and consequently to human health and wellbeing. However, many currently used weed management approaches are increasingly unsustainable. To address this knowledge and practice gap, in June 2014, 35 weed and invasion ecologists, weed scientists, evolutionary biologists and social scientists convened a workshop to explore current and future perspectives and approaches in weed ecology and management. A horizon scanning exercise ranked a list of 124 pre-submitted questions to identify a priority list of 30 questions. These questions are discussed under seven themed headings that represent areas for renewed and emerging focus for the disciplines of weed research and practice. The themed areas considered the need for transdisciplinarity, increased adoption of integrated weed management and agroecological approaches, better understanding of weed evolution, climate change, weed invasiveness and finally, disciplinary challenges for weed science. Almost all the challenges identified rested on the need for continued efforts to diversify and integrate agroecological, socio-economic and technological approaches in weed management. These challenges are not newly conceived, though their continued prominence as research priorities highlights an ongoing intransigence that must be addressed through a more system-oriented and transdisciplinary research agenda that seeks an embedded integration of public and private research approaches. This horizon scanning exercise thus set out the building blocks needed for future weed management research and practice; however, the challenge ahead is to identify effective ways in which sufficient research and implementation efforts can be directed towards these needs.

Combining a weed traits database with a population dynamics model predicts shifts in weed communities.

A functional approach to predicting shifts in weed floras in response to management or environmental change requires the combination of data on weed traits with analytical frameworks that capture the filtering effect of selection pressures on traits. A weed traits database (WTDB) was designed, populated and analysed, initially using data for 19 common European weeds, to begin to consolidate trait data in a single repository. The initial choice of traits was driven by the requirements of empirical models of weed population dynamics to identify correlations between traits and model parameters. These relationships were used to build a generic model, operating at the level of functional traits, to simulate the impact of increasing herbicide and fertiliser use on virtual weeds along gradients of seed weight and maximum height. The model generated 'fitness contours' (defined as population growth rates) within this trait space in different scenarios, onto which two sets of weed species, defined as common or declining in the UK, were mapped. The effect of increasing inputs on the weed flora was successfully simulated; 77% of common species were predicted to have stable or increasing populations under high fertiliser and herbicide use, in contrast with only 29% of the species that have declined. Future development of the WTDB will aim to increase the number of species covered, incorporate a wider range of traits and analyse intraspecific variability under contrasting management and environments.

Cryopreservation disturbs stimulus-response coupling in a platelet subpopulation.

Cryopreservation of platelet suspensions leads to a severe reduction in the functional responses of these cells. This defect primarily resides in a subpopulation which consists of about half the total platelet mass and shows an increased susceptibility to the cryopreservation procedure. Following freeze-thawing this subpopulation failed to aggregate upon stimulation with collagen despite a normal appearance of membrane glycoproteins. Also the contents of alpha granules was similar to the whole suspension and since changes in alpha and dense granule contents often occur in parallel, the poor aggregability could not be attributed to a defect in secretion granules. In contrast, the generation of phosphatidyl-inositol metabolites, the increase in cytosolic Ca2+ content and the phosphorylation of proteins of mol wt 47,000 and 20,000 seen when normal platelets are activated, were completely absent in the subpopulation. These data reveal a severe defect in stimulus-response coupling mechanisms in about half of the platelets after freeze-thawing. The other half of the suspension endures this treatment relatively unharmed and may be used for transfusion.

Differences in the susceptibility of platelets to freezing damage in relation to size.

Previous studies have shown that cryopreservation of normal platelets induces a reduction in the contents of secretion granules, the generation of thromboxane B2, and aggregability. The present study investigates whether these changes in the total population occur to the same extent in four size-dependent subpopulations with mean platelet volumes of 4.2, 5.7, 8.0, and 11.1 microns 3, obtained by counterflow centrifugation. Cryopreservation reduced the contents of the alpha granule markers and the generation of thromboxane B2 in the platelets from the four fractions to the same extent as in the platelets from the total suspension. Maximal aggregation of the platelets in response to collagen was measured by optical aggregation. The average decrease in light transmission after freezing was 47 +/- 3 percent (SEM) for the platelets in the total population, 40 +/- 3 percent for the largest platelets, and 65 +/- 5 percent for the smallest platelets, which indicates that aggregability was better preserved in the larger platelets than in the smaller cells. It is possible that, in the smallest platelets, a decrease in thromboxane generation of approximately 70 percent becomes rate-limiting for aggregation. Further improvements in the clinical use of freeze-preserved platelets may be sought in the preparation of concentrates with relatively high counts of large platelets.

Ultraviolet irradiation modulates MHC-alloreactive cytotoxic T-cell precursors involved in the onset of graft-versus-host disease.

Ultraviolet B (UVB) irradiation of cellular blood components has been proposed as a new technology to prevent HLA sensitization in recipients. Earlier studies have shown that a dose of 2 J/cm2 abrogates the ability of lymphocytes to serve as stimulators in mixed lymphocyte cultures (MLC). In this study we have evaluated the effect of UV energy on T-lymphocytes for the prevention of transfusion-associated graft-versus-host disease (TA-GvHD). The response of cytotoxic T-lymphocyte precursors against host alloantigens was almost undetectable at a dose of 0.5 J/cm2. T-cell proliferation in MLC or in response to phytohaemagglutinin was inhibited by more than 95% at doses of 1 J/cm2 or higher. The data suggest that UV irradiation can be used to prevent both HLA sensitization and TA-GvHD in recipients.

Prevention of MHC-alloimmunization by UV-B irradiation in a murine model: effects of UV dose and number of transfused cells.

The optimal dose of UV-B radiation for prevention of in vivo alloimmunization (AI) against major histocompatibility complex (MHC) antigens was investigated in a murine transfusion model. Two groups with five C57BL/6 mice (H-2b) each were transfused at weekly intervals with 1 x 10(5) or 1 x 10(6) DBA/2 (H-2d) leucocytes. Both suspensions induced anti-H-2d antibodies in all mice after the second transfusion. The minimal UV-B dose required for abolition of alloreactivity in the mixed leucocyte reaction (MLR) was 0.6 J/cm2. This dose completely prevented the onset of MHC-AI in all five mice transfused with six suspensions containing 1 x 10(5) leucocytes. In contrast, suspensions with 1 x 10(6) leucocytes and exposed to 0.6 J/cm2 induced immunization in 4/5 mice. Further increase of the dose to 1.8 or 5.4 J/cm2 did not prevent the onset of MHC-AI. The use of UV radiation for prevention of secondary MHC-AI was investigated in five mice with a primed immune system. Transfusion of suspensions with 1 x 10(5) leucocytes and irradiated at a dose of 1.8 J/cm2 did not prevent booster reactions. We conclude that the number of leucocytes per transfusion determines the efficacy of UV irradiation for the prevention of MHC-AI. For UV irradiation of human platelet concentrates (PCs) we propose to reduce the number of leucocytes by centrifugation prior to UV exposure. UV-B irradiation of PCs with high numbers of leucocytes may not be effective for prevention of alloimmunization.

UVB irradiation of human platelet concentrates does not prevent HLA alloimmunization in recipients.

Exposure of platelet concentrates (PCs) to ultraviolet B radiation (UVB) has been advocated as an alternative method for prevention of the onset of HLA sensitization in recipients. In this study, pooled PCs were irradiated in a Haemonetics UV irradiator (Haemonetics Corp, Braintree, MA) at a dose that did not induce platelet activation. The effect of UVB irradiation on prevention of primary HLA sensitization was evaluated in a prospective controlled clinical study performed in cardiac patients undergoing cardiopulmonary bypass. Patients were treated with filtered red blood cells and a single transfusion of either standard (control group) or UVB-irradiated (UVB group) pooled platelets prepared from 12 donors. Five of 39 patients in the control group and 6 of 62 patients in the UVB group developed allo-antibodies against HLA antigens, which is not significantly different (P = .62). This unexpected finding prompted us to check the efficacy of UVB irradiation. We determined UVB-specific DNA damage in cells by measuring the fluorescence from a labeled specific monoclonal antibody against thymine dimers. With this novel flow cytometer technique, we estimated in UVB-irradiated leukocytes in saline that a mean fluorescence intensity (MFI) of 47 +/- 2 arbitrary units (n = 6) correlated with abolition of alloreactivity in mixed lymphocyte cultures and delayed cell death (within 72 hours). MFI in leukocytes suspended in plasma and exposed to the clinical dose of UVB was sixfold higher (310 +/- 41 arbitrary units) and resulted in early cell death (within 24 hours). We hypothesize that this high level of UVB radiation induces fragmentation of the leukocytes. As a consequence, the poor results of UVB irradiation may be explained by the onset of HLA-alloimmunization induced by soluble donor HLA class I antigens processed and presented by host antigen-presenting cells.

Irradiation of platelets with UV-B light exposes fibrinogen binding sites via an intracellular mechanism.

Previous studies have shown that ultraviolet irradiation (UVI) causes platelet aggregation. In the present study we exposed platelet suspensions to a relatively high dose of UV-B (8 J/cm2) under conditions comparable to those of UVI of platelet concentrates in order to obtain more insight into the UV-induced aggregation response and to evaluate the significance of this phenomenon for the clinical use of UV-irradiated platelet concentrates. This study provides evidence that UV-B induced aggregation is mediated by a Ca2(+)-dependent process of fibrinogen binding to an intact glycoprotein IIb-IIIa complex on platelet membranes. Although UV-induced platelet aggregation is independent of thromboxane A2 formation and ADP secretion, it requires metabolic energy, cytosolic Ca2+ and a low cyclic-AMP level. Thus, UV-B irradiation causes platelet aggregation by exposing fibrinogen binding sites via an intracellular mechanism. Since the amount of bound fibrinogen following UVI is relatively low (about 2,300 molecules platelet) and the binding remains reversible, its effect on platelet behaviour after transfusion may be minor.

Ultraviolet-B irradiation of platelets induces a dose-dependent increase in the expression of platelet activation markers with storage.

Ultraviolet B (UVB) irradiation of platelet concentrates (PCs) has been proposed as a novel technology to prevent HLA sensitization. We have recently reported that 2 J/cm2 of UVB radiation abolishes alloreactive lymphocyte responses in vitro. In order to increase the efficacy of UV irradiation for the prevention of HLA sensitization, we exposed PCs to 4 or 8 J/cm2 of UVB and evaluated the effect of UV radiation on platelet integrity during storage. We report here that UV exposed platelets show a progressive increase in the expression of activation markers P-selectin (GMP-140; CD62) and LIMP-CD63 (GP-53; CD63) on the platelet membrane over time in a dose-dependent manner compared to age-matched controls. Platelet metabolism was also enhanced as evidenced by significant changes in lactate and pH during post-irradiation storage. Based on these findings we transfused PCs within 4 h after UV irradiation. PCs exposed to 4 J/cm2 showed normal post-transfusion recoveries and haemostatic functions, while poor platelet recoveries were found after administration of PCs exposed to 8 J/cm2. We hypothesize that the rapid expression of P-selectin on platelets exposed to the higher dose of UVB leads to an increased binding of these platelets to leucocytes in the circulation resulting in poor platelet recoveries.

Evaluation of a new UVB source for irradiation of platelet concentrates.

The application of ultraviolet B (UVB) radiation has been proposed as a new technology to decrease immunogenicity of leucocytes in platelet transfusions. UV radiation also induces platelet aggregation, which occurs most effectively at wavelengths between 240 and 280 nm and falls off sharply above 300 nm. In order to minimize the effects of UV energy on the platelets we evaluated in this study the expected benefit of a new narrow-band UVB source, emitting a narrow peak around 312 nm. Exposure of platelet or lymphocyte suspensions to this source induced in the platelets both aggregation and functional defects at a dose of 12 J/cm2 and in the lymphocytes inhibition of in vitro function at a dose of 2 J/cm2. A conventional UVB source, emitting a broad spectrum between 280 and 340 nm, was more deleterious for the cells and induced similar defects in the platelets at a dose of 6 J/cm2 and inhibition of lymphocyte function at a dose of 1 J/cm2. These data indicate no benefit for the new UVB source, since the ratio of the doses to induce platelet defects and inhibition of lymphocyte function is identical for each of the two sources. Absorption of UV energy by plasma and the plastic material of platelet containers is another criterium for selection of UV sources. In view of the better transmission characteristics of long wavelength UV energy we propose that there is a preference for the new narrow-band UVB source.

Prevention of donor-specific T-cell unresponsiveness after buffy-coat-depleted blood transfusion.

The immunosuppressive effect of blood transfusions has been demonstrated in several clinical studies. The effect is probably mediated by HLA-class-II-bearing donor leucocytes, because results from laboratory tests show specific down-regulation of the recipient's T-Cell response after administration of blood from donors sharing one HLA haplotype with the recipient. In the present study we evaluated the immunosuppressive potential of buffy-coat-depleted red cell transfusions in patients waiting for renal transplantation, by measuring the frequency of cytotoxic precursor T cells before and after transfusion. The buffy coat was removed from whole blood by the Optipress system and resulted in > 97% depletion of lymphocytes and monocytes. A single transfusion of HLA-haplotype-matched buffy-coat-depleted red cells induced donor-specific down-regulation of T-cell responses in only two of 14 patients. Since HLA-class-II-bearing cells are also involved in the induction of anti-HLA antibodies, we evaluated retrospectively the incident of HLA alloimmunization after a single transfusion of buffy-coat-depleted red cells. No anti-HLA antibodies were found in 140 patients at risk for primary immunization. We conclude that the poor immunological responses found after a single transfusion of HLA-haplotype-matched buffy-coat-depleted red cells is due to the small number of residual HLA-class-II-bearing donor cells. This blood component should not be used for induction of immunosuppression.