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

"1. it should be, it has been for about 20 years, and it's really not much different in the end than breeding animals to have particular traits. there are always concerns about genetically engineered animals/plants affecting the environment in unexpected negative ways, but i can't think of an example where the fears didn't turn out to be baseless.  

first, as you point out, it would be a great advance in pharmacology, to be able to tailor drugs and their doses to me. the pros involve better medical treatment. the cons involve privacy issues like insurance companies denying coverage to people with genetic risk factors. looking at dna markers wouldn't affect the frequency of genetic diseases, but it would allow detection of them earlier. and ok, actually i suppose that if people used this information to avoid having children with genetic diseases, some might decrease in frequency."

producers: apple trees, potatoes, carrots, grains, acorns, cabbage, grass, corn, lettuce

consumers: deer, mice, rabbits, chickens, squirrels, horses, worms, cows

predators: eagles, frogs, wolves, owls