In situ proliferating status of mononuclear cells in rat small bowel grafts

Rat small bowel transplantation was performed in three groups: syngeneic graft, Lewis to Lewis; allogeneic graft, Brown Norway to Lewis; and allogeneic graft with the immunosuppressant FK506 (1 mg/kg). Standard histology and bromodeoxyuridine (BrdU) labelling immunohistochemistry were applied to evaluate the in situ spontaneous proliferating status of the mononuclear cells in the graft lymphoid tissue. In untreated allograft, BrdU-labelling index (BLI) in lamina propria lymphocytes increased significantly on the 5th post-operative day (POD), when no sign of rejection was detected in the villous architecture, compared with isograft (11.8 +/- 2.0% vs 1.9 +/- 0.5%, P < 0.05). Changes in the BLI of lamina propria lymphocyte were also detected on the 3rd and 7th POD, although there were statistically less significant than on the 5th POD. In intraepithelial lymphocytes the changes in BLI were more probably caused by ischaemic damage than immunological reaction. In Peyer's patches and mesenteric lymph nodes, elevation of BLI was specific to rejection like that seen in lamina propria lymphocytes. By administration of FK506, both the elevation of BLI and the histopathological changes were suppressed successfully except for a transient elevation of BLI in Peyer's patches and mesenteric lymph nodes on the 3rd POD.