Final answer:
CD4 cells are also known as helper T cells, which are essential in activating immune responses and aiding in the differentiation of B cells.
Step-by-step explanation:
The cells that are also called CD4 cells are helper T cells (E). Helper T cells play a vital role in the immune response by activating both the antibody and the cell-mediated immune responses. They release cytokines that are crucial for immune system communication and help in the differentiation of B cells into plasma cells that produce antibodies.
It is important to note that cytotoxic T cells, which are CD8+, have a different function of killing infected cells, while helper T cells are focused on assisting other cells in the immune response.