PROBLEM: Previous studies demonstrate increases in the number and granularity of gamma delta T cells within the sheep uterine interplacentomal epithelium during pregnancy. To further characterize their activation and function, gamma delta T-cell receptor (TCR)+ intraepithelial lymphocytes (IELs) from nonpregnant and pregnant uteri were phenotyped extensively. Cytokine mRNA expression in the epithelium and by gamma delta TCR+ IELs isolated from pregnant uteri was also examined. METHOD OF STUDY: Cell suspensions were prepared from the uterine interplacentomal epithelium and from the peripheral blood of nonpregnant and pregnant ewes (120-140 days of gestation). Surface marker expression was determined by two-color flow cytometry and cytokine expression determined by reverse transcriptase--polymerase chain reaction. RESULTS: Uterine gamma delta TCR+ IELs exhibited increased beta 1-integrin expression but decreased leukocyte function associated antigen (LFA)-1 and major histocompatibility complex class I expression during pregnancy. Major histocompatibility complex class II, CD44, CD2, and LFA-3 expression was unchanged during pregnancy, whereas CD25, VLA-4 and L-selectin were never expressed. The same cytokines were expressed in the pregnant and nonpregnant uterine interplacentomal epithelium with detectable mRNA for interferon (IFN)-gamma, tumor necrosis factor (TNF)-alpha, and interleukin (IL)-1 alpha, but not for IL-2 or IL-4. gamma delta TCR+ and CD8+ IEL purified from pregnant uteri expressed mRNA for IFN-gamma, TNF-alpha, transforming growth factor-beta, and IL-10. CONCLUSIONS: gamma delta TCR+ IELs from pregnant uteri have cytoplasmic granules, and express CD8 and cytokines indicative of cytotoxic potential. Phenotypic changes induced during pregnancy differed from those observed after activation of circulating naive cells and may represent further stimulation of fully differentiated effectors. gamma delta TCR+ IELs are present only in interplacentomal areas of pregnant uteri and may control trophoblast invasion within these areas.