Immune Response to Influenza Vaccine in HIV-Infected Individuals

This study will evaluate how HIV infection, including CD4 cell count and viral load, affects the patient's ability to produce antibodies in response to vaccination with the influenza (flu) vaccine. Earlier studies have shown that people with HIV infection do not respond as well as healthy subjects to flu vaccine; that is, they don't make as many antibodies in response to the vaccine. Before the use of current anti-HIV medications, antibodies made to flu vaccination in HIV-positive individuals was related to their CD4 cell count. This trial will examine how CD4 counts and the amount of virus in the blood affect how much and what kind of antibodies the body makes to the flu vaccine. HIV-infected patients and healthy normal volunteers between 18 and 60 years of age may be eligible for this study. Healthy subjects will serve as controls to make sure the flu vaccine works (i.e., stimulates production of enough antibody to protect against the flu), and to compare the amount of antibodies made by HIV-positive and HIV-negative people. Candidates will be screened with a medical history and blood tests (see below). Women who are able to have children will have a pregnancy test. Pregnant women are excluded from the study. Participants will undergo the following procedures: 1. Blood drawing for the following tests: * Routine tests (complete blood count, kidney and liver functions, electrolyte levels). * CD4 cell count. * HLA typing (a genetic marker of the immune system) if it has not already been done at the NIH. This test may be used to try to identify factors associated with the rate of progression of HIV disease or related conditions. Determining HLA type is necessary to be able to perform certain research studies. Some HLA types have been associated with an increased risk of certain diseases like arthritis and other rheumatologic problems. * Viral load (HIV-infected patients only). * Influenza antibody levels. * B cell levels. 2. Flu vaccination 3. Fo