There is ever more evidence that the loss of CD4 cells in people with HIV is sometimes prompted by immune activation—the process whereby a stimulus such as a parasite or HIV itself trips the immune system and viruses replicate more quickly. Michael Lederman, MD, director of the Center for AIDS Research at Case Western Reserve University in Cleveland, says unraveling this process could help identify strategies to help slow or even halt progression to AIDS, including the use of drugs that suppress the immune system.