Choose the most accurate characteristic of Class II MHC proteins. A)They dampen the responses of other T cells and of B cells. B)They divide to produce memory cells and more active helper T cells. C)They are found in the plasma membranes of all nucleated cells. D)They consist of circulating proteins that assist antibodies in the destruction of pathogens. E)They are found in the membranes of lymphocytes and antigen-presenting cells.