Age-related changes of immunophenotypically immature lymphocytes in normal human peripheral blood

The presence of phenotypically immature lymphocytes in umbilical cord blood has been a controversial topic. Moreover, their changes with age have not been systematically evaluated. In the present study, relative and absolute numbers of CD34+, CD10+CD19+, and CD4+CD8+ cell subsets were determined in umbilical cord blood from 12 full-term normal newborns, 43 children aged 1 month to 6 years, and 10 young adults. The samples were processed by whole-blood lysis and monoclonal antibody staining, and cells were analyzed by flow cytometry. Immature cells were present in cord blood and progressively declined in both absolute and percentage numbers with age, each according to a particular curve, reaching youth values roughly at age 2-4 years. These results demonstrate that phenotypically immature cells normally circulate at low levels in peripheral blood, mostly at birth and during infancy, but also during youth.