Interleukin-12 up-regulates perforin- and Fas-mediated lymphokine-activated killer activity by intestinal intraepithelial lymphocytes.

Human intraepithelial lymphocytes (IELs) comprise a unique compartment of memory T cell receptor (TCR)-alphabeta( +)CD8(+) T lymphocytes interspersed between intestinal epithelial cells. They develop potent lymphokine-activated killer (LAK) activity with interleukin (IL)-15, a cytokine that is found in excess in certain mucosal inflammatory states. IL-12, released by activated antigen-presenting cells, is known to potentiate perforin-induced cytotoxicity. This study evaluates the mechanism by which IL-12 up-regulates LAK activity. When IELs were stimulated with IL-15, the CD94(+) IEL subset expanded and carried out cytotoxic activity in redirected lysis against P815 cells as well as Fas ligand (FL)- and tumour necrosis factor (TNF)-alpha-mediated lysis of Jurkat and WEHI cells, respectively. IL-12 enhanced the perforin- and FL-, but not TNF-alpha-mediated events. In addition, the up-regulated killing of HT-29 cells by IL-12 was reduced by concanamycin (which targets perforin) and antibody neutralizing FL but not by anti-TNF-alpha antibody. Furthermore, IL-12 augmented IL-15-stimulated release of serine esterases as well as expression of perforin and FL by IELs, but not TNF-alpha. This study shows that LAK activity, carried out by the CD94(+) IELs, involves perforin, FL and TNF-alpha. IL-12 up-regulates the first two mechanisms of action, showing for the first time its effect on FL production and lytic activity.