Cutting edge: TCR alpha beta(+) CD8 alpha alpha(+) T cells are found in intestinal intraepithelial lymphocytes of mice that lack classical MHC Class I molecules

TCR alpha beta(+) intestinal intraepithelial lymphocytes (IEL) can express either the typical CD8 alpha beta heterodimer or an unusual CD8 alpha alpha homodimer, Both types of CD8(+) IEL require class I molecules for their di fferentiation, since they are absent in beta(2)m(-/-) mice. To gain insight into the role of class I molecules in forming TCR alpha beta(+) CD8(+) IEL populations, we have analyzed the IEL in mite deficient for either TAP, be ta(2)m, CD1, or K and D. We find that K-/-D-/- mice have TCR alpha beta(+) CD8 alpha alpha(+) IEL, although they are deficient for TCR alpha beta(+) C D8 alpha beta(+) cells. This indicates that at least some TCR alpha beta(+) CD8 alpha alpha(+) IEL require only nonclassical class I molecules for the ir development. Surprisingly, the TCR alpha beta(+) CD8 alpha alpha(+) IEL are significantly increased in K-/-D-/- mice, suggesting a complex interact ion between CDS' IEL and class I molecules that might include direct or ind irect negative regulation by K and D, as well as positive effects mediated by nonclassical class I molecules.