Prevention of superantigen-induced down-regulation of T-cell mediated cytotoxic activity by IL-2 in vivo

Administration of staphylococcal enterotoxin A (SEA) to mice induces profound activation, cytokine production and cytotoxic activity of both CD4(+) and CD8(+) T cells, but subsequently activated cells are deleted or become anergic. This study demonstrates that administration of interleukin-2 (IL-2) can prevent sea-induced hyporesponsiveness in CD8(+) cytotoxic T lymphocytes (CTL). Repeated injections with sea every fourth day resulted in severly reduced cytotoxic activity in the spleen, which correlated with a reduced number of sea-responsive T-cell receptor (TCR)-V beta 11(+)CD8(+) cells. Studies of purified TCR-V beta 11(+)CD8(+) cells showed that they possessed intact cytotoxic activity per cell compared with cells from mice given a single injection of SEA, indicating that deletion was the main mechanism for the reduced cytotoxic activity. Combined treatment with SEA and IL-2 increased the number of cytotoxic cells in the spleen after each SEA injection and prevented the down-regulation of cytotoxic activity. Increased cytotoxic activity could be related to increased number and proliferation of CD8(+)IL-2R alpha(+) cells, suggesting that administration of IL-2 maintained IL-2 responsiveness among CD8(+) cells. Studies of sorted TCR-V beta 11(+)CD8(+) cells demonstrated that combined treatment with SEA and IL-2 also increased cytotoxic activity per cell compared with treatment with SEA alone. Taken together, IL-2 administration in vivo augmented SEA-induced expansion of T cells as well as the cytotoxic activity per CTL, and prevented SEA-induced cell deletion.