Perhaps more important is that the secondary response of antibodies has a higher affinity binding for these antigens. These latter antibodies will bind to antigen even when complexed to antibody and help clear the antigen more effectively from the circulation. It is important remember, however, that B cells alone do not respond to antigen directly, even in the presence of APC cells. They must have a second signal, normally provided by the T cells. This point was elegantly shown in a series of transfer experiments using irradiated recipient animals.