Age-Related Increase in the Frequency of CD4+ T Cells That Produce Interferon-γ in Response to Staphylococcal Enterotoxin B during Childhood

Background. The susceptibility of infants to infections is well defined clinically, and immunologic abnormalities have been described. Immune maturation is complex, however, and the interval during which changes occur during childhood has not been identified. Methods. To assess age-related differences in the CD4(+) T cell responses, we evaluated the frequency of CD4(+) T cells that produced interferon (IFN) gamma in response to staphylococcal enterotoxin B (SEB) stimulation in 382 healthy infants and children (2 months to 11 years of age) and 66 adults. Flow cytometry was used to assess SEB-induced CD69 and CD40 ligand (CD40-L) expression and IFN-gamma production by CD4(+) and CD45RO(+)CD4(+) T cells. Results. CD69 and CD40-L expression by CD4(+) and CD45RO(+)CD4(+) T cells were similar to adult levels from infancy, but the frequency of activated T cells that produced IFN-gamma remained lower than adult responses until children were 10 years of age. Conclusions. These observations indicate that the IFN-gamma response of CD4(+) T cells to SEB remains limited for a much longer interval than was reported elsewhere, extending to the second decade of life. Observed differences in CD45RO(+)CD4(+) T cell function indicate that CD4(+) T cells with the same phenotypes do not possess equivalent functional capabilities.