And let's suppose the APC is a B lymphocide. In such a case, the helper T cell, which is our CD four T cell, will stimulate that B lymphocyte, our APC to actually begin to undergo mitosis and create more clone cells, identical cells that contain the same exact B cell receptor. And they can also stimulate those B lymphocytes to actually undergo the process of differentiation and differentiate into plasma cells and memory B cells. So plasma cells are those cells that produce antibodies while memory B cells store a copy of that antibody in case reinfection ever takes place. Now, instead of the CD four being a helper T cell, let's suppose we have some other type of T lymphocyte that binds to, let's say, a macrophage. In such a case, we can actually stimulate the cell mediated immunity.