Comparison of T cell functional changes during childhood with the ontogeny of CDw29 and CD45RA expression on CD4+ T cells.

The ontogeny of the peripheral blood mononuclear cells' responsiveness to various activators during childhood was studied and compared to the expression of CDw29 and CD45RA molecules at the surface of CD4+ T cells. The results show that newborn peripheral blood mononuclear cells are characterized by a responsiveness to mitogens that is higher than that observed in adults, at least shortly after stimulation. This contrasts with a clear decreased response to CD2 and CD3 MAb at any time after stimulation. These functional characteristics correlate with a low density of CDw29 antigen on virtually all CD4+ T cells and a high density of CD45RA antigen on most CD4+ T cells at birth. These patterns of reactivity and phenotype are similar to those found among naive adult T cells. When ageing, the response to mitogens becomes rapidly similar to the adult's values, whereas the responses to CD2 or CD3 MAb are more gradually acquired. This slow rate of functional changes grossly parallels the increase of CDw29+ CD4+ and the decrease of CD45RA+ CD4+ T cell subsets. These changes finally lead to the immunophenotypic and functional characteristics that are typical of adult memory T cells. These results suggest that iterative antigenic stimulations both induce memory T cells and create the conditions to improve the overall immune competence.