CD98 is a 125 kD disulfide-linked heterodimer protein also known as 4F2 and FRP-1. It is broadly expressed on activated and transformed cells (hematopoietic and non-hematopoietic), and at low levels on quiescent cells. CD98 has been characterized as a potential amino acid transporter (neutral and dibasic amino acids) that is involved in lymphocyte activation and integrin signaling. CD98 is composed of a light chain (45 kD) and a heavy chain (80 kD). Studies with knock-out mice indicate that the CD98 heavy chain is involved in integrin-dependent cell spreading and protection against anchorage deprivation-induced apoptosis. The MEM-108 antibody is useful for flow cytometry and immunoprecipitation.