| Objective:Transplantation of peripheral nerve or Schwann cells can enhance neuronal survival,axonal regeneration and functional recovery after spinal cord injury (SCI).Microcapsulated technology is a kind of effective immune isolation means which has developed in recent years. It can isolate macromolecule immunologic active material and protect transplantation of xeno-or allograft in microcapsule against the attack of host immune system. But, whether microcapsules can forbid antigen presentation is rare be researched. This experiment is to observe the influence of the MHC II expression on the spinal cord half transection injury of adult rat after transplantation of the microencapsulated sciatic nerve tissue allograft, and study the effect of microcapsules to graft rejection and the possible repair mechanism of spinal cord injury.Methods:Experiments were performed in 32 adult Wistar rats and 96 adult Sprague-Dawley (SD) rats of either sex, weighing 200-250 g. Then all of the rats were randomly divided into four groups: Group A(transplantation of microencapsulated sciatic nerve tissue/cells, n=24), Group B (transplantation of tissue/cells suspension, n=24), Group C (empty microcapsules control,n=24 ), Group D (single injury control, n=24). After dividing, modified Tarlov score was enforced on right hindlimb of rats. Bilateral sciatic nerves pretreated from Wistar rats were dissected under sterile conditions and made into nerve tissue/cells suspension. Following centrifugation at a low speed, the tissue/cells were mixed with 1.5% sodium alginate solution, which was then extruded into 20mmol/L barium solution by using a droplet generation device, forming microencapsulated sciatic nerve tissue/cells suspension. Group A, B,C and D were performed a right hemisection injury of spinal cord at T8 level, where were transplanted with the gelatin sponge sticking 10μl microencapsulated nerve tissue/cells suspension, the gelatin sponge sticking 10μl tissue/cells suspension, sticking 10μl empty microcapsules and the gelatin sponge, respectively.. At 10d,21d,35d and 60d after SCI, six rats of each group were anesthetized and perfused transcardially with 4% paraformaldehyde (PH7.4), following modified Tarlov score on right hindlimb. The tissue of 10mm spinal cord arround the lesion site and its corresponding spinal ganglia was taken out. After the tissues got were performed the paraffin sections, which were dealed with Hematoxylin-eosin (HE) staining and anti-MHC II immunohistochemistry. .Results : Group B elicited high major histocompatibility complex(MHC)-II expressing within and around the allografts compared with other three groups at 10d,21d after grafting, especially at 21d(P<0.05), but significantly reduced after 35d(P<0.05). A large number of inflammatory cells could be seen in the tissue of spinal cord arround the lesion site at 21d,35d.At 60d, there were many infiltration of inflammatory cells and hyperplasia glial cells yet.Compared with Group B, the numbers of MHC-II immunopositive cells in Group A were significantly low (P<0.05). There was no remarkable inflammatory response evidence at 35d, and appeared some cells that had characteristics of neuron. But the number of MHC II immunopositive cells increased a small quantity after 60d(P>0.05), there were only a few leukocytes and macrophages infiltration around grafts. In addition, lots of neurons appeared. At 10d,21d there were some MHC II immunopositive cells in Group C and Group D, but significantly reduced after 35d(P<0.05), and disappeared at 60d. Group C had no obvious difference compared with Group D at every time(P>0.05). MHC-II immunopositive cells were not seen in spial ganglia of four groups rats at every time. The right hind limb modified Tarlov score of locomotive function of every group was normal before surgery, but it was low and no difference among every group at 10d after SCI. After that, it was gradually ascending. The comparison between Group A and Group B ,C or D existed the difference at 21d (P <0.05). The score of Group A was significantly superior to that of Group B ,C and D at 35d and 60d, whose difference was remarkable (P<0.01), but it didn't reach the normal level. The locomotive function of right hindlimbs in rats got recovered to a greater or less extent, but Group A was the best one.Conclusions:MHC II antigen molecules are highly expressed in transplanting sciatic nerve tissue allograft, it suggest that there is a rejection existing in sciatic nerve tissue allograft. The barium alginate membranes can protect allgraft from immunological rejection and down-regulate the MHC II expression to some extent. The changes of MHC II expression in spinal glial cells are in parallel with the degree of infiltration of inflammatory cells , it suggest that the changes of MHC II expression are correlated with immunological rejection around the allografts positively. The allotransplantation of microencapsulated sciatic nerve tissue/cells can improve the recovery of injured neuron.
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