AIDS: New research shows how the host's response to HIV infection may affect the progression of the disease in an individual. When exposed to HIV, the body responds by producing cytokines, which appear to inhibit HIV replication. Two cytokines, IL-2 and IL-6, have been studied in vitro, and two newly discovered receptors, CCKR5 and fusin, also appear to play a significant role in disease progression. Further testing in humans is needed to fully understand the interplay of these substances.