Invariant natural killer T cells are a newly described kind of lymphocyte delineated first in mice and then in humans. They often express CD4 antigen, a few express CD8, and others (double-negative cells) express neither CD4 nor CD8. It is characteristic of invariant natural killer T cells that they express a restricted number of T-cell receptors, respond to glycolipid antigens, and on activation rapidly produce large amounts of both type 1 …