ACTIVATED ALPHA-BETA-CD8-ALPHA-CD8+,TCR-ALPHA-BETA+ MURINE INTESTINALINTRAEPITHELIAL LYMPHOCYTES CAN MEDIATE PERFORIN-BASED CYTOTOXICITY, WHEREAS BOTH SUBSETS ARE ACTIVE IN FAS-BASED CYTOTOXICITY(, BUT NOT ALPHA)

CD8 single-positive (CD8(+)) T cells in murine intestinal intraepithel ial lymphocytes (iIEL) consist of alpha alpha-CD8+ and alpha beta-CD8( +) subpopulations. Cytotoxicity represents an important function of pe ripheral CD8(+) T cells, so we examined perforin-granzyme-based and Fa s-based cytotoxicity of activated CD8(+) TCR-alpha beta(+) ilEL subset s. We found that allospecific CTL activity was induced from alpha beta -CD8(+) ilEL but not from alpha alpha-CD8(+) ilEL even when allospecif ic TCR were present on the ilEL, as demonstrated by using 2C TCR trans genic mice. On the other hand, both CD8(+) iIEL subsets proliferated u pon allostimulation with a lower responder frequency than CD8(+) LN ce lls. The alpha alpha-CD8(+) TCR-alpha beta(+) iIEL appeared to lose th eir ability to perform perforin-based killing after activation through TCR because fresh cells lysed P815 cells coated with anti-TCR beta-ch ain (TCR-beta) mAb, whereas cells activated by plate-bound anti-TCR mA b did not. Of interest, both activated CD8(+) TCR-alpha beta(+) ilEL s ubsets, but not fresh cells, were able to mediate Fas-based killing wh en triggered with PMA and Ca2+ ionophore.