Development of CD8 alpha/beta(+) TCR alpha beta intestinal intraepithelial lymphocytes in athymic nu/nu mice and participation in regional immune responses

On the basis of the CD8 coreceptor expression, T-cell receptor (TCR)alpha beta-bearing intestinal intraepithelial lymphocytes (i-IEL) segregate into two populations. The CD8 alpha alpha(+) TCR alpha beta i-IEL develop thymus independently, whereas the CD8 alpha beta(+) TCR alpha beta i-IEL are generally considered to be thymus dependent. Flow cytometry analysis revealed a distinct population of CD8 alpha beta(+) TCR alpha beta i-IEL in individual athymic nu/nu mice. The i-IEL encompassing CD8 alpha beta(+) TCR alpha beta cells expressed potent cytolytic and interferon-gamma-producing activities. These findings demonstrate that CD8 alpha beta(+) TCR alpha beta i-IEL can develop in nu/nu mice independently from a functional thymus and suggest that these cells, directly or indirectly, perform biological functions in the gut.