A population of murine gamma delta T cells that recognize an inducible MHCclass lb molecule

Although gamma delta T cells are implicated in regulating immune responses, gamma delta T cell-ligand pairs that could mediate such regulatory functio ns have not been identified. Here, the expression of the major histocompati bility complex (MHC) class Ib T22 and the closely related T10 molecules is shown to be activation-induced, and they confer specificity to about 0.4% o f the gamma delta T cells in normal mice. Thus, the increased expression of T22 and/or T'10 might trigger immunoregulatory gamma delta T cells during immune responses. Furthermore, the fast on-rates and slow off-rates that ch aracterize this receptor/ligand interaction would compensate for the low li gand stability and suggest a high threshold for gamma delta T cell activati on.