THE CHONDROITIN SULFATE FORM OF INVARIANT CHAIN CAN ENHANCE STIMULATION OF T-CELL RESPONSES THROUGH INTERACTION WITH CD44

Invariant chain (Ii) is a nonpolymorphic glycoprotein that associates with major histocompatibility complex class II molecules and has been shown to mediate several functions in class II-restricted antigen pres entation. A small proportion of Ii is modified by the addition of chon droitin sulfate (Ii-CS), and this form of Ii is associated with class II on the surface of antigen-presenting cells. In this report we show that expression of Ii-CS dramatically enhanced the ability of class II -positive EL4 transfectants to stimulate class II-dependent allogeneic and mitogenic T cell responses. Antibody blocking studies and the abi lity of CD44 to bind directly to Ii-CS suggest that Ii-CS can function as an accessory molecule during T cell responses through interactions with CD44.