Dipyridamole for Immune Activation in HIV

Background: * Since HIV-infected individuals started taking anti-HIV medications, illnesses from AIDS have decreased, but other serious diseases have increased. Researchers think this may be caused by an increase in activity of the immune system that fights infection, leading to inflammation. Inflammation is a normal body reaction to any infection. However, if inflammation lasts a long time, like in HIV infection, it may lead to complications such as heart disease, cancer, liver disease, lung disease, and problems with thinking. Many HIV researchers are studying the harmful effects of this prolonged immune system activity and inflammation and possible ways to prevent these complications. * A drug called dipyridamole is approved by the Food and Drug Administration (FDA) under the trade name Persantine® for use with other drugs to reduce the risk of blood clots after heart valve replacement. Laboratory studies have shown that dipyridamole also lowers the level of immune system activity and inflammation measured in the blood. Objectives: * To see how dipyridamole affects blood and lung tests to measure immune system activity and inflammation and to look at the safety and tolerability of dipyridamole in people infected with HIV. This use of dipyridamole is investigational, or not approved by the FDA; however, the dose to be used in this study, 100mg four times a day, is the dose approved by the FDA. Eligibility: * Individuals 18 years of age and older who have HIV infection and are taking medications to treat it, and have a low viral load (HIV-1 RNA \<50 copies/mL) for a minimum of 12 months. Design: * Participants will be screened with a physical exam, blood test, and medical history. Women of reproductive age will also receive a pregnancy test. * Participants will take either Dipyridamole or a placebo for 12 weeks. Then they will take Dipyridamole for 12 weeks. * During the study, participants will have frequent blood and urine tests. Dipyridamole drug levels, and liver and kidney function tests will be performed. HIV viral load (the amount of virus in the blood) will also be studied. * Participants will have a final follow-up visit after an additional 4 weeks. * Four brachial artery ultrasound images will be taken. * Four pre- and post-bronchodilator spirometry tests will be performed by participants enrolled under Version 2.0: after each pre-test spirometry, participants will be asked to inhale 4 puffs of albuterol, and then to repeat the spirometry for post-testing. * Participants will receive rectal swabs at screening, and four flexible sigmoidoscopies with rectal biopsies of the sigmoid colon throughout the study. These studies of the lower colon and samples of the rectum will be used to explore the effects of Dipyridamole. Participants can, however, opt out of all rectal procedures.