Inclusion Criteria:

• Documentation of HIV infection with a positive HIV ELISA and confirmatory Western Blot.
• Age equal to or greater than 18 years.
• CD4 cell count > 350/µL at screening.
• No receipt of any antiretroviral therapies within the six months prior to screening.
• No anticipated need for any antiretroviral therapies during the course of this study, as determined by the principal investigator or by the subject's HIV caregiver.

Note: There is no HIV-1 RNA level eligibility criterion.

Exclusion Criteria:

• Inability to complete written, informed consent.
• Incarceration at the time of any screening or main study visit.
• Diagnosed vascular disease (history of angina pectoris, coronary disease, peripheral vascular disease, cerebrovascular disease, aortic aneurysm, or otherwise known atherosclerotic disease).
• Diagnosed disease or process, besides HIV infection, associated with increased systemic inflammation (including, but not limited to, systemic lupus erythematosis, inflammatory bowel diseases, other collagen vascular diseases).

Note: Hepatitis B or C co-infections are NOT exclusionary

• History of bleeding diathesis, gastrointestinal ulceration or bleeding, cerebrovascular aneurysm or bleeding, or retinal hemorrhage.
• Known or suspected malignancy requiring systemic treatment within six months of screening.
• History of ADA-defined diabetes mellitus [134]

Note: History of gestational diabetes is not exclusionary if the potential subject does not have current ADA-defined diabetes.

• History of migraine headaches.
• History of Raynaud's phenomenon.
• History of cardiac arrhythmias or cardiomyopathy.
• History of hypothyroidism or hyperthyroidism, even if treated.
• Known allergy or intolerance to pentoxifylline or other methylxanthines (e.g. theophylline, caffeine, theobromine).

Note: Use of caffeinated products, except on the mornings of the study visits, is not exclusionary.

• Known allergy or intolerance to nitroglycerin.
• History of carotid bruits.
• Creatinine clearance < 50mL/min (using the Cockcroft-Gault equation, see Appendix 1) using a serum creatinine level measured within 28 days prior to screening or at screening.
• Hemoglobin < 9.0mg/dL within 28 days of screening or at screening.
• Alanine aminotransferase (ALT) level or aspartate aminotransferase (AST) > 3 times ULN within 28 days of screening or at screening.
• Total bilirubin > 2.5 times ULN within 28 days prior to screening or at screening.
• Fever, defined as T ≥ 38.0C within 48 hours prior to screening.

Note: Fever within 48 hours prior to each main study visit will require postponement of that study visit until the patient has defervesced (T < 38.0C) for at least 48 hours; fevers continuing past the allowed study visit timeframe will result in study discontinuation.

-Therapy for acute infection or other serious medical illnesses within 14 days prior to screening.

Note: Therapy for acute infection or other serious medical illnesses that overlaps with a main study visit will result in postponement of that study visit until the course of therapy is completed; postponement outside of the allowed study visit timeframe will result in study discontinuation.

• Pregnancy or breastfeeding during the course of the study.
• Hypotension, defined as systolic blood pressure < 90mmHg, at time of screening.

Note: Hypotension noted prior to brachial artery reactivity testing on each main study visit will result in study visit postponement of at least one day until systolic pressure is ≥ 90mmHg the morning of brachial reactivity testing; postponement outside of the allowed study visit timeframe will result in study discontinuation.

• Hypertension, defined as the receipt of any antihypertensive medication within 28 days prior to screening or systolic blood pressure > 160mmHg at screening.
• Receipt of anti-inflammatory agents (including, but not limited to, plaquenil, infliximab, etanercept, mycophenolate mofetil, sirolimus, tacrolimus, cyclosporine, pentoxifylline, thalidomide) within 28 days of screening.
• Receipt of investigational agents, cytotoxic chemotherapy, systemic or topical glucocorticoids (of any dose), or anabolic steroids within 28 days of screening.

Note: Physiologic testosterone replacement therapy is not exclusionary.

• Receipt of lipid-lowering drugs, aspirin, other NSAIDS, acetazolamide, anticoagulants, anticonvulsants, or thyroid replacements within 28 days prior to screening.
• Use of sildenafil, vardenafil, or tadalafil within 72 hours (before or after) of each main study visit.
• Active drug or alcohol use or dependence that, in the opinion of the investigator, would interfere with adherence to study requirements.