The role of the A and E molecules as restriction elements was examined in the F antigen system. In the mouse the only responder haplotype known to date is k, and blocking studies with a monoclonal antibody show that in vitro T-cell proliferation is restricted by the Ak molecule. The (CBA X DBA/2)F1 hybrid, which is a responder X nonresponder cross, is itself a nonresponder in terms of F-specific antibody production. Up to 10 days after priming, (CBA X DBA/2)F1 T cells exhibited an F-specific proliferative response, but this diminished rapidly at later times VSports手机版. This diminution could be blocked with an E-specific monoclonal antibody, suggesting that suppression is restricted by the E molecule. .