Increased T-cell division in healthy children and children infected with HIV. (A) The proportion of dividing naive and memory CD4⁺ T cells was high in healthy infants (○) and declined with increasing age. In children infected with HIV (•), the proportion of dividing T cells was significantly higher than in healthy children. (B) The observed age-related decline in Ki67 expression in children infected with HIV most likely reflects a selection bias. Longitudinal analysis in a subset of older patients of whom cryopreserved samples of earlier time points were available showed that Ki67 expression by CD4⁺ T cells was already low at those earlier time points. See Table 2 for nonparametric Spearman correlation coefficients.