The purpose of this study is to learn more about some of the immune cells in the blood (CD4 cells, for example) of healthy children in order to better understand the differences in the blood cells of children infected with HIV.

Because children's bodies are still developing, their cells are different from those of adults, and their bodies respond differently to infections such as HIV. In order to understand how immune cells grow and mature so that they can fight HIV, it is important to see how these cells behave in normal children.

Early in life, the cells involved in immune selection differentiate into CD4+ and CD8+ cells. Currently there is insufficient information on the cell maturation and activation of these peripheral blood mononuclear cell (PBMC) subsets in normal children. The critical need for this information has been brought about by the pediatric HIV/AIDS epidemic, which requires the measurement of peripheral blood CD4+ T cells and other cells types for interpretation of HIV disease progression. The immunopathogenesis of pediatric HIV infection differs from that in adults but is not well understood. In order to better understand HIV disease progression in HIV-infected children, these PBMC subsets must be studied in normal children so that control values can be established.

Healthy infants, children, and adolescents presenting for routine care or elective surgery have a single blood sample obtained. Blood is used for complete blood count, peripheral blood mononuclear cell flow analysis for surface markers, and plasma and cell storage. Demographic information including age, sex, race, and ethnicity is obtained at the time of the blood draw. The reason for the patient's visit is also documented. No study drugs are administered or supplied as part of this study. Statistical analysis is used to estimate the median distribution of each CD4 and CD8 subset.

Inclusion Criteria

A child may be eligible for this study if he/she:

• Is 0 - 18 years old.
• Is HIV-negative and is born to an HIV-negative mother.
• Is healthy (no serious infection or disease).
• Has signed informed consent of a parent or legal guardian if under 18.

Exclusion Criteria

A child will not be eligible for this study if he/she:

• Is pregnant or breast-feeding.
• Has already completed this study once before.
• Is taking prescription medications other than prescription vitamins.