Your patient is living with HIV infection and has not developed AIDS. She knows that her CD4 count is carefully monitored, and she asks why this test is important. How would you explain the role of CD4 cells?

A."CD4 cells are special lymphocytes (white blood cells) that activate other immune cells and direct your body's response to invaders."
B."CD4 cells produce complement, which enhances several processes in the immune response."
C."CD4 cells attack and kill bacteria as they enter the body."
D."CD4 cells produce antibodies that disable antigens if they breach the body's first line of defense