Allosensitization after transplant failure: the role of graft nephrectomy and immunosuppression - a retrospective study.

There are conflicting data about the role of transplant nephrectomy and immunosuppression withdrawal on the development of allosensitization and the impact on re-transplantation. We divided 109 first graft recipients into two groups according to whether they underwent nephrectomy (NX+, n = 61) or their graft was left in situ (NX-, n = 48). Sera were assessed for HLA-A/B/Cw/DR/DQ antibodies at the time of NX/transplant failure and after 3, 6, 12, 24 months. The NX+ group showed a higher rate of donor specific antibody (DSA) and non-DSA human leukocyte antigen (HLA) antibody production at all the time points. Multivariable analysis showed that nephrectomy was a strong, independent risk factor for the development of DSAs after 12 and 24 months (P = 0.005 and 0.008). In the NX- group, low tacrolimus levels correlated with DSA formation (AUC 0.817, P = 0.002; best cut-off level 2.9 ng/ml). Analysis with a standardized pool of UK donors showed a more difficult grade of HLA matchability following nephrectomy compared with the NX- group. Nephrectomy is followed by the long-term production of DSA and non-DSA HLA antibodies and negatively impacts on the chances of finding a HLA-compatible kidney. Tacrolimus levels ≥3 ng/ml are protective against the development of allosensitization and could facilitate re-transplantation in the NX- group.

Flower constancy in honey bee workers (Apis mellifera) depends on ecologically realistic rewards.

As first described by Aristotle, honey bee (Apis mellifera) workers show a strong tendency to visit flowers of only one type during a foraging trip. It is known that workers rapidly learn a flower colour when rewarded with artificial nectar (sucrose solution). However, some previous studies report that the degree of constancy after training is unaffected by reward quantity and quality when bees are tested in an array of artificial flowers of two easily distinguished colours, such as blue and yellow. One possible reason for this surprising result is that large reward volumes were compared. This is likely to mask the abilities of foragers to make adaptive decisions under more realistic conditions. To test this possibility, we offered untrained honey bee workers ecologically relevant rewards (0.5, 1 or 2 µl of 0.5 or 1 mol l(-1) sucrose solution) on one or two consecutive yellow or blue artificial flowers and then recorded which flowers the bees subsequently landed on in an array of 40 empty flowers. The results showed that an increase in all three factors (volume, concentration and number of rewards) significantly increased constancy (proportion of visits to flowers of the trained colour) and persistence (number of flowers visited) during the foraging bout. Constancy for the least rewarding situation was 75.9% compared with 98.6% for the most rewarding situation. These results clearly show that honey bee workers do become more constant to blue or yellow with increasing nectar rewards, provided that the rewards used are ecologically realistic. As the most rewarding conditions led to nearly 100% constancy, further reward increases during training would not have been able to further increase constancy. This explains why previous studies comparing large rewards found no effect of reward on constancy.