We have shown, in a rat model of immunodeficiency, permanent alterations in the thymus and in the gut-associated lymphoid tissues. We observed by immunohistochemistry an increase in the number of gamma/delta+ T cells in the gut lamina propria and in the number of CD8alpha/alpha+, CD25+, gamma/delta+ subpopulations of intestinal intraepithelial lymphocytes (iIEL). The aim of the present study was to analyze the isolated rat iIEL by flow cytometry. Materials and Methods Cells from mesenteric lymph nodes were examined in parallel with isolated iIEL. After staining with different antibodies, samples were run on a FACScan flow cytometer. Background staining was evaluated using isotype controls. Data analysis was performed using Lysys II software (Becton Dickinson) and WinMDI 2.3 software.1) CD8alpha/beta populations do not express TCRgamma/delta, 2) CD8alpha/alpha+ populations express TCRgamma/delta, and its percentage is significantly increased in R21, 3) CD8alpha/beta and CD8alpha/alpha iIEL express TCRalpha/beta, being the percentage of CD8alpha/alpha+ TCRalpha/beta+ iIEL increased and the percentage of CD8alpha/beta+ TCRalpha/beta+ iIEL decreased in R21, and 4) CD8alpha/alpha as well as CD8alpha/beta iIEL do express CD25 only in R21.Considering the above results, we conclude that there exists an "in situ" origin and extrathymic maturation of the CD8alpha/alpha+ iIEL in the intestinal epithelium. The increase of TCRgamma/delta+ T cells may be triggered by the carbohydrate dextrin, to provide immune protection and control of inflammation at the intestinal level.