Characteristics of Immunity in Gut Mucosa, Spinal Fluid, Lymph Node and Blood of HIV Negative Thais and Thais With HIV Infection

Inclusion Criteria: 1. Age 18 to 50 years old 2. HIV negative subjects must have negative results by 4th generation EIA and NAT (Aptima) 3. HIV positive subjects must have a positive 4th generation EIA and a positive less sensitive EIA. 4. Understand the study and sign informed consent form. Persons who cannot read will have the consent form read to them by a study staff and they can give informed consent by using thumb print. Exclusion Criteria: 1. Have gastrointestinal disorders or gastrointestinal symptoms that require endoscopy for diagnostic purposes or have systemic disorders, which include but may not be limited to autoimmune diseases such as rheumatoid arthritis, systemic lupus erythematosus or psoriasis, that in the judgment of investigators could cause colon mucosa to be abnormal on biopsy 2. Active AIDS-defining opportunistic infection (OI) within 30 days prior to entry for HIV-positive subjects. Subjects must be off all acute treatments for OI for at least 14 days prior to entry. Subjects on maintenance or prophylactic therapy for AIDS-related OIs will be eligible. 3. Have platelet count \< 150,000 count/ml or PT, PT/PTT \> the upper limit of normal (ULN) or INR \> 1.1 4. Have self-reported bleeding disorder 5. Untreated syphilis infection 6. Abnormal screening neurological examination suggestive of central neurological findings if planning to participate in the lumbar puncture 7. Positive urine pregnancy test 8. Persons who have a history of a medical or psychiatric disorder by investigator's interview and physical examination according to standard practices, that in the judgment of the investigator(s), would interfere with or serve as a contraindication to adherence to the study protocol or ability to give informed consent.