INCREASE IN INTRAEPITHELIAL LYMPHOCYTES AS AN EARLY MARKER OF REJECTION IN A FULLY ALLOGENEIC RAT SMALL-BOWEL TRANSPLANTATION MODEL

In a model of fully allogeneic heterotopic rat small bowel transplanta tion, the changes in intraepithelial lymphocyte (IEL) number and subpo pulations were analysed. During early phases of rejection (5th postope rative day) a 4-fold increase in the number of IEL was observed when c ompared with native small bowel (4.05 vs. 15.84 IEL/100 epithelial cel ls). When cyclosporine was given, counts were still as high as 11.4 an d 12.58 on the 5th and 10th postoperative days, respectively. The perc entage of CD8+ IEL, constituting a major population (84%) in the untre ated small bowel, was significantly decreased (46.4%) during early pha ses of rejection. At that time, the majority of intraepithelial mononu clear cells were both CD8- and CD4-. In cyclosporine-treated animals, this was not observed until the 10th postoperative day. Some 23 % of I EL in untreated animals expressed MHC class I antigens of the host; 17 .2% (5th postoperative day) and 19.8 % (10th postoperative day) did so in the cyclosporine-treated animals. Transmission electron microscopy revealed lymphocytes that bore cytoplasmic buds and pseudopods protru ding between the enterocytes. There was no morphological difference be tween the IEL of rejected allografts and native small bowel. Due to th e unspecific histologic changes associated with rejection, interpretat ion of histopathologic findings in mucosa biopsies of the allograft ca n be rather troublesome. An increase in the number of IEL is therefore a welcome additional marker of rejection.