To identify molecules that modulate T cell functions, we have established a monoclonal antibody that recognizes CD98 heavy chain; the next results showed that anti-CD98hc mAb can suppress fibronectin-mediated cell spreading but not amino acid transport. Furthermore, anti-CD98hc mAb significantly suppressed T cell proliferation in mixed lymphocyte reaction. Thus, these results indicated that anti-CD98 mAb may prevent and treat T cell mediated autoimmune diseases in the future.