Rat nigral xenografts survive in the brain of MHC class II-, but not class I-deficient mice

We hake examined the role of the indirect path a of antigen recognition and T cells in neural xenografts rejection by using major histocompatibility complex (MHC) class II-deficient mice as xenograft recipients. Dissociated embryonic ventral mesencephalic tissue from Sprague-DaMey rats was stereotaxically injected as a cell suspension into the striatum of MHC class II-deficient adult mice as well as MHC class I-deficient and wild-type mice as controls. All of the MHC class II-deficient mice had surviving grafts in the striatum 4 weeks post-grafting. In contrast, only a few of the MHC class I-deficient mice exhibited very small grafts and none of the wild-type mice had any surviving grafts. The mean number of surviving transplanted dopamine neurons in the MHC class II-deficient group was significantly larger than that observed in the other two groups. Moderate levels of MHC class I antigen expression were seen in the transplantation sites of some animals in the MHC class II-deficient group, No helper or cytotoxic T cells were observed infiltrating into the graft sites of this group. However, there were markedly increased levels of expression of MHC class I and class II antigens, and a number of T cells infiltrating in the graft sites in both the MHC class I-deficient and wild-type groups, These results show that rat embryonic nigral tissue can survive transplantation in the brain of the MHC class II-deficient mice for at least 4 cheeks without any overt signs of rejection. suggesting that the indirect path a of foreign antigen recognition mediated by host MHC class II molecules and helper T cells plays an important role in the rejection responses to intracerebral xenografts. (C) 2002 IBRO, Published by Elsevier Science Ltd. All rights reserved.