Comparison of immune response to nerve allograft segments in fetal and adult rabbits: A histological study

Fetuses, as opposed to adults, are immature immunologically and it has been proved that they can tolerate allograft materials much better than adults. In this study the rejection phenomenon of nerve allografts was compared hi stologically in fetuses and adults. The study was performed in 60 New Zeala nd rabbits (30 pregnant and 30 nonpregnant), and allograft nerve segments w ere obtained from Chinchilla rabbits. The animals were divided into fetal a nd adult groups. Each group was studied at various time periods. Nerve allo grafts were placed under the panniculus carnosus in the interscapular regio n of the fetuses and adults. In both fetal and adult groups, the nerve allo graft segments were assessed histologically after 1, 7, and 30 days. The cr iteria used during the evaluation were the degenerative findings in the mye linated axons (large, medium, and small axons), changes in Schwann's cells, and the quantity of infiltrating cells. The changes were graded microscopi cally from 0 (no change) to 3 (severe destruction and cellular infiltration ). Cellular infiltration was more extensive in the adult groups than in the fetal groups. Earlier fetal groups showed minimal infiltration, but the re sponse became more extensive in the later fetal groups. This is probably re lated to the removal of the fetuses from their intrauterine environment. Wh en comparing fetal and adult groups, the results were significant (p < 0.05 ). The fetuses tolerated the nerve allograft segments better than the adult s. This may be related to the immature immune system of the fetuses.