Age-dependent appearance of NK1.1+ T cells in the livers of beta2-microglobulin knockout and SJL mice.

NK1.1+ T cells, a specialized set of T cells that recognize CD1, are reportedly absent in young beta2-microglobulin-deficient (beta2m-knockout (KO)) and SJL mice. In this study, we show that a significant number of NK1.1+ T cells exist in the livers of older beta2m-KO and SJL mice, and that the number of liver NK1.1+ T cells increases as the animals age. The surface phenotypes of liver NK1.1+ T cells from beta2m-KO and SJL mice were similar to NK1.1+ T cells from C57BL/6 mice, except that the bulk of these cells were CD4- CD8-. After anti-CD3 injection in vivo, the cells promptly expressed IL-4 mRNA just as NK1.1+ T cells did in normal mice. Using L cells expressing CD1, liver NK1.1+ T cells from both beta2m-KO and SJL mice were stimulated to proliferate, although to a lesser degree than were such cells from C57BL/6 mice. Our studies show that some NK1.1+ T cells accumulate in the livers of older beta2m-KO and SJL mice, and that they appear to have functional properties similar to "normal" NK1.1+ T cells.