Studies of allotransplantation of bone using immunohistochemistry and radioimmunoassay in rats.

Immunohistochemistry and radioimmunoassay were used to study the rejection mechanism of allografted bone tissue in rats through changes in major histocompatibility complex (MHC) antigen expression by osteocytes in the allograft and in alloantibody levels in the serum of the host rats. Some osteocytes in normal rat bone tissue expressed MHC Class I antigen, and the degree of expression varied among the osteocytes. The expression of MHC Class I antigens on osteocytes of allografted bone tissue increased with time after allograft transplantation. When DA strain bone tissue was allografted to F344 strain host tissue, a marked decrease in the number of osteocytes was observed, and almost all of the remaining osteocytes strongly expressed MHC Class I antigens in the allografted bone tissue three weeks after transplantation. F344 strain rat recipients with DA strain rat bone grafts showed high titers of anti-Class I alloantibody. These titers increased two weeks after transplantation. Major histocompatibility complex Class I antigens on osteocytes may play an important role in allograft rejection, as has been observed in other transplanted organs in the rat.