MOUSE CD4 BINDS MHC CLASS-II WITH EXTREMELY LOW-AFFINITY

Interaction of CD4 with MHC class II molecules plays a crucial role du ring thymic development and activation of single-positive CD4 T lympho cytes. The quantitation of this interaction is, therefore, important f or understanding the role of CD4 during these events. To this end, we have developed a rosette assay, which enabled us to study this molecul ar interaction. By coupling soluble mouse CD4 onto beads, we could sho w specific binding of CD4 to MHC class II molecules on A20 B lymphoma cells. These binding studies revealed an extremely low affinity (K(a) less-than-or-equal-to 10(4) M-1) between CD4 and MHC class II molecule s in mouse.