Meta-analysis reveals that pollinator functional diversity and abundance enhance crop pollination and yield.

How insects promote crop pollination remains poorly understood in terms of the contribution of functional trait differences between species. We used meta-analyses to test for correlations between community abundance, species richness and functional trait metrics with oilseed rape yield, a globally important crop. While overall abundance is consistently important in predicting yield, functional divergence between species traits also showed a positive correlation. This result supports the complementarity hypothesis that pollination function is maintained by non-overlapping trait distributions. In artificially constructed communities (mesocosms), species richness is positively correlated with yield, although this effect is not seen under field conditions. As traits of the dominant species do not predict yield above that attributed to the effect of abundance alone, we find no evidence in support of the mass ratio hypothesis. Management practices increasing not just pollinator abundance, but also functional divergence, could benefit oilseed rape agriculture.

Development of a pathway model to assess the exposure of European pine trees to pine wood nematode via the trade of wood.

Pine wood nematode (PWN), Bursaphelenchus xylophilus, is a threat for pine species (Pinus spp.) throughout the world. The nematode is native to North America, and invaded Japan, China, Korea, and Taiwan, and more recently Portugal and Spain. PWN enters new areas through trade in wood products. Once established, eradication is not practically feasible. Therefore, preventing entry of PWN into new areas is crucial. Entry risk analysis can assist in targeting management to reduce the probability of entry. Assessing the entry of PWN is challenging due to the complexity of the wood trade and the wood processing chain. In this paper, we develop a pathway model that describes the wood trade and wood processing chain to determine the structure of the entry process. We consider entry of PWN through imported coniferous wood from China, a possible origin of Portuguese populations, to Europe. We show that exposure increased over years due to an increase in imports of sawn wood. From 2000 to 2012, Europe received an estimated 84 PWN propagules from China, 88% of which arose from imported sawn wood and 12% from round wood. The region in Portugal where the PWN was first reported is among those with the highest PWN transfer per unit of imported wood due to a high host cover and vector activity. An estimated 62% of PWN is expected to enter in countries where PWN is not expected to cause the wilt of pine trees because of low summer temperatures (e.g., Belgium, Sweden, Norway). In these countries, PWN is not easily detected, and such countries can thus serve as potential reservoirs of PWN. The model identifies ports and regions with high exposure, which helps targeting monitoring and surveillance, even in areas where wilt disease is not expected to occur. In addition, we show that exposure is most efficiently reduced by additional treatments in the country of origin, and/or import wood from PWN-free zones. Pathway modelling assists plant health managers in analyzing risks along the pathway and planning measures for enhancing biosecurity.

Quantification of motility of carabid beetles in farmland.

Quantification of the movement of insects at field and landscape levels helps us to understand their ecology and ecological functions. We conducted a meta-analysis on movement of carabid beetles (Coleoptera: Carabidae), to identify key factors affecting movement and population redistribution. We characterize the rate of redistribution using motility µ (L2 T-1), which is a measure for diffusion of a population in space and time that is consistent with ecological diffusion theory and which can be used for upscaling short-term data to longer time frames. Formulas are provided to calculate motility from literature data on movement distances. A field experiment was conducted to measure the redistribution of mass-released carabid, Pterostichus melanarius in a crop field, and derive motility by fitting a Fokker-Planck diffusion model using inverse modelling. Bias in estimates of motility from literature data is elucidated using the data from the field experiment as a case study. The meta-analysis showed that motility is 5.6 times as high in farmland as in woody habitat. Species associated with forested habitats had greater motility than species associated with open field habitats, both in arable land and woody habitat. The meta-analysis did not identify consistent differences in motility at the species level, or between clusters of larger and smaller beetles. The results presented here provide a basis for calculating time-varying distribution patterns of carabids in farmland and woody habitat. The formulas for calculating motility can be used for other taxa.

Scenario approach for assessing the utility of dispersal information in decision support for aerially spread plant pathogens, applied to Phytophthora infestans.

Opportunities exist to improve decision support systems through the use of dispersal information gained from epidemiological research. However, dispersal and demographic information is often fragmentary in plant pathology, and this uncertainty creates a risk of inappropriate action whenever such information is used as a basis for decision making. In this article, a scenario-based simulation approach is used to evaluate crop and economic risks and benefits in the use of dispersal information for decision making using the potato late blight pathosystem (Phytophthora infestans-Solanum tuberosum) as a case study. A recently validated spatiotemporal potato late blight model was coupled to submodels for crop growth, tuber dry matter production, and fungicide efficacy. The yield response of a range of management scenarios to a single influx of primary inoculum (the initial spore load) was calculated. Damage curves (relative yield loss versus initial spore load) from a range of combinations of varietal susceptibility and fungicide treatments were used to classify the various management scenarios as either sensitive to initial spore load or tolerant to initial spore load, thus identifying where a high degree of accuracy would be required in dispersal information for appropriate decision making, and where a greater degree of uncertainty could be tolerated. General epidemics, resulting from spatially homogeneous initial spore loads, responded more strongly to the size of the initial spore load than focal epidemics, resulting from an initial spot infection. Susceptible cultivars responded with sizeable yield losses even at low levels of initial spore load, regardless of the fungicide management regime used. These results indicated that, for susceptible cultivars (late cultivars in particular), the degree of accuracy that would be required in dispersal information for appropriate decision making is unlikely to be practically attainable. The results also indicated that, contrary to "folk wisdom," spore loads of a few hundred spores per square meter do not lead to appreciable crop loss in resistant cultivars and are therefore acceptable. We conclude that scope exists for including dispersal information in decision making for potato late blight with resistant potato cultivars but not for susceptible cultivars. The modeling framework used in this study can be extended to investigate the scope for inclusion of dispersal information in decision support for other aerially transmitted pathogens.

Parameterization and evaluation of a spatiotemporal model of the potato late blight pathosystem.

A spatiotemporal, integrodifference equation model of the potato late blight pathosystem is described. Formerly, the model was used in a theoretical context to analyze and predict epidemic dynamics in spatially heterogeneous mixtures of host genotypes. The model has now been modified to reflect a research interest in interactions between genotype, environment, landscape, and management. New parameter values describing host-pathogen interactions were determined and new environment-pathogen relationships included. A new analytical equation describing lesion expansion and associated necrosis has also been developed. These changes prompted a need to assess the quality of model predictions. Cultivar-isolate-specific interactions were characterized in the model using three quantitative components of resistance: infection efficiency, lesion growth rate, and sporulation intensity. These were measured on detached potato leaflets in the laboratory. Results of a sensitivity analysis illuminate the effect of different quantitative components of resistance and initial conditions on the shape of disease progress curves. Using the resistance components, the epidemic process of lesion expansion was separated from the epidemic process of lesion propagation providing two reference curves for diagnosing observed epidemics. The spatial component of the model was evaluated graphically in order to determine if realistic rates of focal expansion for potato late blight are produced. In accordance with theory, the radius of a predicted focus increased linearly with time and a constant focal velocity was reached that compared well with published experimental data. Validation data for the temporal model came from 20 late blight epidemics observed in field trials conducted in the Netherlands in 2002 and 2004. The field data and model were compared visually using disease progress curves, and numerically through a comparison of predicted and observed t(5) and t(50) points (time in days until 5 and 50% disease severity is reached, respectively) and relative areas under the disease progress curve values. Temporal model predictions were in close agreement with observational data and the ability of the model to translate measured resistance components, weather data, and initial conditions into realistic disease progress curves without the need for calibration confirms its utility as a tool in the analysis and diagnosis of epidemics.

Modeling the rejection probability in plant imports.

Phytosanitary inspection of imported plants and flowers is a major means for preventing pest invasions through international trade, but in a majority of countries availability of resources prevents inspection of all imports. Prediction of the likelihood of pest infestation in imported shipments could help maximize the efficiency of inspection by targeting inspection on shipments with the highest likelihood of infestation. This paper applies a multinomial logistic (MNL) regression model to data on import inspections of ornamental plant commodities in the Netherlands from 1998 to 2001 to investigate whether it is possible to predict the probability that a shipment will be (i) accepted for import, (ii) rejected for import because of detected pests, or (iii) rejected due to other reasons. Four models were estimated: (i) an all-species model, including all plant imports (136,251 shipments) in the data set, (ii) a four-species model, including records on the four ornamental commodities that accounted for 28.9% of inspected and 49.5% of rejected shipments, and two models for single commodities with large import volumes and percentages of rejections, (iii) Dianthus (16.9% of inspected and 46.3% of rejected shipments), and (iv) Chrysanthemum (6.9 and 8.6%, respectively). All models were highly significant (P < 0.001). The models for Dianthus and Chrysanthemum and for the set of four ornamental commodities showed a better fit to data than the model for all ornamental commodities. Variables that characterized the imported shipment's region of origin, the shipment's size, the company that imported the shipment, and season and year of import, were significant in most of the estimated models. The combined results of this study suggest that the MNL model can be a useful tool for modeling the probability of rejecting imported commodities even with a small set of explanatory variables. The MNL model can be helpful in better targeting of resources for import inspection. The inspecting agencies could enable development of these models by appropriately recording inspection results.

Spatial and temporal patterns of carabid activity-density in cereals do not explain levels of predation on weed seeds.

Seed predation is an important component of seed mortality of weeds in agro-ecosystems, but the agronomic use and management of this natural weed suppression is hampered by a lack of insight in the underlying ecological processes. In this paper, we investigate whether and how spatial and temporal variation in activity-density of granivorous ground beetles (Coleoptera: Carabidae) results in a corresponding pattern of seed predation. Activity-density of carabids was measured by using pitfall traps in two organic winter wheat fields from March to July 2004. Predation of seeds (Capsella bursa-pastoris, Lamium amplexicaule, Poa annua and Stellaria media) was assessed using seed cards at the same sites and times. As measured by pitfall traps, carabids were the dominant group of insects that had access to the seed cards. In the field, predation of the four different species of seed was in the order: C. bursa-pastoris>P. annua>S. media>L. amplexicaule; and this order of preference was confirmed in the laboratory using the dominant species of carabid. On average, seed predation was higher in the field interior compared to the edge, whereas catches of carabids were highest near the edge. Weeks with elevated seed predation did not concur with high activity-density of carabids. Thus, patterns of spatial and temporal variation in seed predation were not matched by similar patterns in the abundance of granivorous carabid beetles. The lack of correspondence is ascribed to effects of confounding factors, such as weather, the background density of seeds, the composition of the carabid community, and the phenology and physiological state of the beetles. Our results show that differences in seed loss among weed species may be predicted from laboratory trials on preference. However, predator activity-density, as measured in pitfall traps, is an insufficient predictor of seed predation over time and space within a field.

Production ecology of agroforestry systems: a minimal mechanistic model and analytical derivation of the land equivalent ratio.

In this paper, the yield and the land equivalent ratio (LER) of a silvo-arable agroforestry (SAF) system, containing one tree and one crop species, is analyzed analytically using a minimal mechanistic model describing the system dynamics. Light competition between tree and crop is considered using light extinction functions. The tree leaf area is driven by annual increase in the number of leaf-bearing shoots with a seasonal cycle of bud burst, leaf expansion and senescence. The crop leaf area dynamics is driven by the solar radiation, heat sum and the dry matter allocation to the leaves. As a consequence of this, the model consists of six state equations expressing the temporal dynamics of: (1) tree biomass; (2) tree leaf area; (3) number of shoots per tree; (4) crop biomass; (5) crop leaf area index, and (6) heat sum. The main outputs of the model are the growth dynamics and final yields of trees and crops. Daily inputs are temperature and radiation. Planting densities, initial biomass of tree and crop species and growth parameters must be specified. The main parameters are those describing light interception, conversion to dry matter and leaf area. Given the crop cover and the tree parameters, it is shown that under potential growing conditions the land equivalent ratio can be explicitly expressed in terms of these parameters.

A novel approach to bilateral hand-assisted laparoscopic nephrectomy for autosomal dominant polycystic kidney disease.

PURPOSE: Laparoscopic nephrectomy in patients with autosomal dominant polycystic kidney disease (ADPKD) is technically challenging. We describe our technique and present our experience with a transperitoneal hand-assisted laparoscopic (HAL) technique using a standard vacuum curettage system to reduce the size of the kidneys thereby facilitating nephrectomy. MATERIALS AND METHODS: A retrospective review was completed of 10 consecutive patients undergoing bilateral HAL nephrectomy between March 2002 and October 2004 using the following technique. A hand port is positioned through a 6-7 cm periumbilical incision and port sites are placed at the midclavicular line (12 mm) and anterior axillary line (5 mm) on the side of the initial nephrectomy. After the renal vessels are divided and the kidney is completely mobilized a 12 mm curette is inserted through the medial port site. The Berkeley VC-10 Vacuum Curettage System (ACMI, Southborough, MA) is used to morcellate and aspirate the kidney providing a significant decrease in the overall size and allowing easy extraction through the midline incision. The procedure is repeated for the contralateral side. RESULTS: All 10 patients underwent successful bilateral HAL nephrectomy with a mean operative time of 194 minutes. The average length of stay was 4.7 days. Patients with renal allografts had stable function at the time of discharge. The average size of the kidneys removed was 717 g and average length was 19 cm. All patients did well postoperatively with complete resolution of their presenting symptoms. CONCLUSION: In patients with symptomatic ADPKD, bilateral HAL nephrectomy using the vacuum curettage system to minimize the size of the kidneys is fast, safe and effective.

Host finding by Uscana lariophaga (Hymenoptera: Trichogrammatidae) in stored cowpea: the effect of distance, time interval, host patch size and spatial orientation.

Host finding and parasitization by Uscana lariophaga Steffan, a potential biocontrol agent of the storage pest Callosobruchus maculatus (Fabricius), were investigated in stored cowpea. Host finding was shown to be a function of distance, time, host patch size and the spatial position of U. lariophaga relative to the host patch. Uscana lariophaga females were able to find hosts up to 75 cm horizontal distance from the host patch, which was the largest distance tested. The probability that a host patch was found when an individual U. lariophaga female was released at 2.5 cm horizontal distance from the host patch ranged from 0.6 after 2 h foraging time to 0.9 after 8 h foraging time. At 10 cm from the host patch, host finding probability ranged from 0.2 to 0.45 at these respective foraging times. Finding probabilities doubled compared to horizontal distances when U. lariophaga was released below the host patch, and halved when it was released above the host patch. The negative geotaxic response was shown not to be an artefact of the release method. The median net displacement rate in the direction of the host patch was two beans per hour (1.4 cm h(-1)). The results suggest that U. lariophaga females start searching for hosts regardless of the quality of the olfactory information they receive. Additional observations indicated that U. lariophaga is adapted to a host with a patchy distribution, which implies that host finding over larger distances is relevant for U. lariophaga.

Influence of host diversity on development of epidemics: an evaluation and elaboration of mixture theory.

ABSTRACT A spatiotemporal/integro-difference equation model was developed and utilized to study the progress of epidemics in spatially heterogeneous mixtures of susceptible and resistant host plants. The effects of different scales and patterns of host genotypes on the development of focal and general epidemics were investigated using potato late blight as a case study. Two different radial Laplace kernels and a two-dimensional Gaussian kernel were used for modeling the dispersal of spores. An analytical expression for the apparent infection rate, r, in general epidemics was tested by comparison with dynamic simulations. A genotype connectivity parameter, q, was introduced into the formula for r. This parameter quantifies the probability of pathogen inoculum produced on a certain host genotype unit reaching the same or another unit of the same genotype. The analytical expression for the apparent infection rate provided accurate predictions of realized r in the simulations of general epidemics. The relationship between r and the radial velocity of focus expansion, c, in focal epidemics, was linear in accordance with theory for homogeneous genotype mixtures. The findings suggest that genotype mixtures that are effective in reducing general epidemics of Phytophthora infestans will likewise curtail focal epidemics and vice versa.

Modeling Spatial Characteristics in the Biological Control of Fungi at Leaf Scale: Competitive Substrate Colonization by Botrytis cinerea and the Saprophytic Antagonist Ulocladium atrum.

ABSTRACT A spatially explicit model describing saprophytic colonization of dead cyclamen leaf tissue by the plant-pathogenic fungus Botrytis cinerea and the saprophytic fungal antagonist Ulocladium atrum was constructed. Both fungi explore the leaf and utilize the resources it provides. Leaf tissue is represented by a two-dimensional grid of square grid cells. Fungal competition within grid cells is modeled using Lotka-Volterra equations. Spatial expansion into neighboring grid cells is assumed proportional to the mycelial density gradient between donor and receptor cell. Established fungal biomass is immobile. Radial growth rates of B. cinerea and U. atrum in dead cyclamen leaf tissue were measured to determine parameters describing the spatial dynamics of the fungi. At temperatures from 5 to 25 degrees C, B. cinerea colonies expanded twice as rapidly as U. atrum colonies. In practical biological control, the slower colonization of space by U. atrum thus needs to be compensated by a sufficiently dense and even distribution of conidia on the leaf. Simulation results confirm the importance of spatial expansion to the outcome of the competitive interaction between B. cinerea and U. atrum at leaf scale. A sensitivity analysis further emphasized the importance of a uniform high density cover of vital U. atrum conidia on target leaves.

Anti-interleukin-2 receptor therapy in combination with mycophenolate mofetil is associated with more severe hepatitis C recurrence after liver transplantation.

The pathogenesis of hepatitis C virus (HCV) recurrence after liver transplantation (LT) is poorly understood, but the cellular immune response is likely to have a major role. Daclizumab, an interleukin-2 receptor (IL-2R) antibody that blunts T-cell activation, leading to a decreased risk for cellular rejection, is used frequently in transplant recipients. The aim of this study is to evaluate the effect of daclizumab therapy on the incidence and severity of recurrent HCV. Forty-one liver transplant recipients (21 patients, HCV positive; 20 patients, HCV negative) at high risk for neurological or renal complications of calcineurin inhibitors were administered daclizumab, mycophenolate mofetil (MMF), and steroids in the early post-LT period, followed by tacrolimus and a steroid taper. All patients were followed up prospectively for graft function and disease recurrence with protocol liver biopsies day 7, month 4, and yearly. Compared with patients without HCV, patients with HCV administered daclizumab had greater 4-month serum alkaline phosphatase, total bilirubin, and alanine aminotransferase (ALT) levels. These biochemical differences resolved by 12 months, except for persistent elevation of ALT levels. Compared with a well-matched HCV control population, patients with HCV administered daclizumab were more likely to have an earlier onset of hepatitis, jaundice, and greater histological activity. Recurrent hepatitis progressed more rapidly in the daclizumab group; 45% developed advanced disease within 1 year. HCV viral load in the daclizumab group was significantly greater at both 4 months and 1 year. Results of this study suggest that the use of adjuvant IL-2R antibodies in combination with MMF in the early peritransplantation period may be associated with early recurrence of hepatitis C and more rapid histological progression of disease.

Resection of the inferior vena cava for hepatic malignancy.

Involvement of the inferior vena cava (IVC) by hepatic tumors, although uncommon, is considered to be unresectable by standard surgical techniques. Recent advances in hepatic surgery have made combined hepatic and vena caval resection possible. The purpose of this study is to describe the surgical techniques and early results of combined resection of the liver and IVC. From 1997 to 2000, 11 patients underwent resection of the IVC along with four to seven liver segments. Resections were carried out for hepatocellular carcinoma (four); colorectal metastases (four); and hepatoblastoma, gastrointestinal stromal tumor metastases, and squamous cell carcinoma in one patient each. Ex vivo procedures were performed twice, and total vascular isolation was used in the nine other cases. The IVC was reconstructed with ringed Gore-Tex tube graft (five), primarily (five), or with Gore-Tex patches (one). There were two early deaths: one from liver failure at 3 weeks and one from sepsis secondary to a perforated segment of small bowel 4 months postresection. One patient with a gastrointestinal stromal tumor died at 32 months of recurrent tumor and one patient with hepatocellular carcinoma is alive with recurrent tumor at 16 months. The remaining patients are alive and disease free with follow-up ranging from 3 to 40 months without evidence of IVC occlusion. Combined resection of the liver and IVC is a formidable undertaking with substantial surgical risk. However, this aggressive surgical approach offers a chance for cure in patients with tumors involving the IVC that would otherwise have a dismal prognosis.

What happens to renal transplant recipients who lose their grafts?

Little attention has been given to the fate of patients who lose their grafts. We reviewed outcomes of 438 recipients of first renal allografts who underwent transplantation at our institution between January 1, 1988, and December 31, 1997, and lost their grafts or died with a functioning transplant. Of the 438 patients, 168 patients died with a functioning transplant. The most common causes of death were cardiac disease, infection, and cancer. Patients who died with a functioning graft were older (>49 years, 64.3%) than patients who died after returning to dialysis therapy or who are still alive (>49 years, 25.9%). Eighty-six patients (39%) who returned to dialysis therapy were again placed on a cadaveric waiting list. Only 44 patients received a second transplant, of which 30 transplants (68.2%) are still functioning. Our study shows that relatively few patients who lose kidney transplants are returned to the cadaveric waiting list and even fewer undergo retransplantation.

Outcome of kidney transplants in patients known to be flow cytometry crossmatch positive.

BACKGROUND: The clinical significance of the flow cytometry crossmatch has been addressed in several retrospective studies, but the results have been controversial. There are no prospective studies in which patients known to be antibody positive underwent transplantation. METHODS: The flow cytometry crossmatch was performed prospectively in 1130 renal transplant recipients. A decision to perform transplantation was based on whether the positive results were on T or B cells, in the current or peak specimen, and taking into account the presence or absence of other immunological risk factors. One hundred antibody-positive patients received a transplant. Graft survival and rejection episodes were analyzed in this group and compared with 100 crossmatch-negative patients matched for age, sex, race, and time of transplantation. RESULTS: The incidence of rejection at 1 month was higher in antibody-positive patients (26%) than in antibody-negative patients (12%, P<0.01). Early rejection seemed to be more frequent in antibody-positive patients regardless of whether the antibodies were current or historic, or against T or B cells. There were more steroid-resistant rejections in antibody-positive than in antibody-negative patients. However, biopsy specimens showed that vascular lesions that can be associated with humoral rejection were not more frequent in the antibody-positive patients than in the controls. There were no differences in graft survival between the two groups. CONCLUSIONS: Low-level preformed alloantibodies detected by flow cytometry represent a risk of rejection even for patients purposely selected for having no additional immunological risk factors. The risk seems to be due to donor-specific memory rather than to a direct effect of the antibodies. The results indicate that flow cytometry provides useful information to assess donor-recipient compatibility.

Liver transplantation for hepatocellular carcinoma.

OBJECTIVE: To analyze patient and tumor characteristics that influence patient survival to select patients who would most benefit from liver transplantation. SUMMARY BACKGROUND DATA: The selection of patients with hepatocellular carcinoma (HCC) for liver transplantation remains controversial. METHODS: One hundred twelve patients with nonfibrolamellar HCC who underwent a liver transplant from 1985 to 2000 were reviewed. Survival was calculated using the Kaplan-Meier method, with differences in outcome assessed using the log-rank procedure. Multivariate analysis was then performed using a Cox regression model. RESULTS: Overall patient survival rates were 78%, 63%, and 57% at 1, 3, and 5 years, respectively. Patients infected with the hepatitis B virus had a worse 5-year survival than those who were not (43% vs. 64%), with most deaths being attributed to recurrent hepatitis B. However, patients with hepatitis B virus who underwent more recent transplants using antiviral therapy fared as well as those who were negative for the virus, showing a 5-year survival rate of 77%. Patients with vascular invasion by tumor had a worse 5-year survival than patients without vascular invasion (33% vs. 68%). Vascular invasion, tumor size greater than 5 cm, and poorly differentiated tumor grade were predictors of tumor recurrence by univariate analysis; however, only vascular invasion remained significant on multivariate analysis: the rate of tumor recurrence at 5 years was 65% in patients with vascular invasion and only 4% for patients without vascular invasion. CONCLUSIONS: For well-selected patients with HCC, liver transplantation in the current era can achieve equivalent results to transplantation for nonmalignant indications. Vascular invasion is an indicator of high risk of tumor recurrence but is difficult to detect before transplantation.

Susceptibility of liver allografts to high or low concentrations of preformed antibodies as measured by flow cytometry.

Liver grafts are more resistant to damage by HLA antibodies than other organ allografts, but it is not clear if the antibodies are associated with graft rejection or graft loss, or if different antibody concentrations have different effects. To explore potential associations between antibody concentrations and outcome, preformed IgG antibodies against donor cells were quantified by flow cytometry in 465 consecutive liver transplant recipients. Antibody-positive patients were classified according to whether they had high or low antibody concentrations and analyzed for possible correlation with graft rejection or graft loss. The results showed that the incidence of rejection was not significantly different between antibody-positive and negative patients. However, patients with high antibody concentrations had a higher incidence of steroid-resistant rejections (31% at 1 year) than patients with low antibody (4%) or no antibody (8%, p < 0.0004). These effects were mainly due to T-cell (HLA class 1) antibodies. The overall incidence of rejection at 1 year was 69% for high antibody patients, 51% for patients with low antibodies and 53% for patients with no antibodies (p not significant). In an apparent paradox, antibody-positive patients underwent fewer early graft losses. Thus, the associations of preformed antibodies and outcome depend, on the one hand, on antibody concentrations, and on the other hand on whether the outcome measured is steroid-sensitive rejection, steroid-resistant rejection or graft survival. These complex interactions may explain the controversial results observed in previous studies.