these results are compatible with a two-signal requirement for the activation of b cells and may be explained as follows : ( a ) the mitogen , in absence of immunogen , stimulates those clones which have received a specific signal from cross-reacting structures in the environment : ( b ) instead , no cross-reaction are available for the conformation-controlled structure of the `` '' activating '' '' determinant ;
C1155003
activation
C0003320
immunogen