LIGHT, a new TNF superfamily member, is essential for memory T helper cell-mediated activation of dendritic cells.

LIGHT is a recently identified member of the TNF superfamily that is up-regulated on activated T cells and can cooperate with CD40L to condition DC for the priming of CTL. In this report, we show that an intracellular pool of LIGHT is found selectively in some CD45RA-CD27+CD4+ "central" memory T cells and to a greater extent in some CD45RA-CD27-CD4+ effector memory T cells. LIGHT, like CD40L, is rapidly up-regulated on memory CD4+ T cells upon activation. Unlike CD40L, LIGHT up-regulation on naive T cells is delayed. Stimulation of DC with each subset of memory T cells in the presence of superantigen revealed that CD40L and LIGHT are required for optimal secretion of IL-12. Moreover, effector memory T cells, which can interact with DC in peripheral tissues, contribute to CCR7 induction on DC. LIGHT and CD40L can also regulate IL-12 production by CCR7+ DC capable of migration to lymph nodes. These data suggest that both LIGHT and CD40L may be involved in the maintenance or reactivation of secondary Th1 responses.