It is the central hypothesis of the investigators study that HIV disease is a pro-inflammatory condition, and that years of inflammation result in premature "aging' of the immune system ("immunosenescence"). Just as these changes are thought be causally associated with heart disease in the very old,the investigators postulate that these changes will be associated with early heart disease in the untreated and perhaps treated HIV disease. To address this hypothesis, the investigators will measure immunosenescence in a large cohort of patients who span the entire disease process.

Inclusion Criteria:

• HIV controllers: positive for HIV by standard antibody serological determinations with undetectable HIV RNA level (< 75 copies RNA/mL) in absence of therapy
• HIV non-controllers: detectable HIV RNA levels in absence of therapy
• Highly active anti-retroviral therapy responders (HAART responders): on combination antiretroviral therapy with undetectable HIV RNA levels.
• HIV-seronegative participants will also be studied.

Exclusion Criteria:

• Treated individuals that changed antiretroviral regimen within 12 weeks prior to study enrollment.
• Individuals who have started or stopped antihypertensive medication or lipid lowering medication or changed doses of these drugs within 12 weeks of the study will be excluded.
• As nitroglycerin is administered to assess endothelium-independent vasodilation, we also plan to exclude patients who have taken sildenafil, vardenafil, or tadalafil within 72 hours of the endothelial function study, or who are hypotensive (systolic BP <100).

Treated and untreated HIV-infected individuals and HIV-uninfected individuals.