Figure 3.

Examples of the changes in cell surface phenotype of CD4⁺ (top) and CD8⁺ (bottom) T lymphocytes that occur with age. Note that in early childhood the majority of CD4⁺ T cells have a CD4⁺ CD45RA⁺CD45RO⁻ naive phenotype, whereas in older adults most CD4⁺ T cells have a CD45RA⁻CD45RO⁺ memory phenotype. Similar changes occur in CD8⁺ T cells. Boxed areas indicate windows that were used to sort cells with the indicated phenotype as well as the gates that were used to calculate the percentage of cells with a given phenotype shown in Table .