During its development, each B-lymphocyte becomes genetically programmed, through a process called gene translocation, to make a unique antibody molecule that will function as a B-cell receptor. Molecules of that antibody are then placed on the cell's surface where it can react with epitopes of an antigen. A B-lymphocyte with an appropriately fitting B-cell receptor can now react with epitopes of an antigen having a corresponding shape. This activates the B-lymphocyte. Cytokines from an activated T4-lymphocyte now enable the activated B-lymphocyte to proliferate into a large clone of identical B-lymphocytes. During this time, "fine-tuning" of the B-cell receptor occurs as a result of affinity maturation. The B-lymphocytes now differentiate into antibody-secreting B-lymphocytes and plasma cells that secrete large quantities of antibodies "fitting" the original epitope. Some B-lymphocytes differentiate into B-memory cells capable of anamnestic response.