CD4 helper T cell recognized a processed protein antigens displayed by professional APC ,and are activated to proliferate and differentiate into effector cells. These T effector cells begin to migrate toward lymphoid follicles. Naive B lymphocytes, which reside in the follicles, recognize antigens in this site and are activated to migrate out of the follicles.The two cell populations come together at the edges of follicle and interact.In the activated B cell , how is the Ig molecule on B cell surface related to what is presented on MHC11. And what are these Ig doing?