Lymphocyte subpopulations in pediatric age. Definition of reference values by flow cytometry

In the present paper we have analyzed the age-related changes in the distribution and numbers per cubic millimeter of the circulating lymphocyte subpopulations. Lymphocyte subsets have been examined by monoclonal antibodies specific for surface antigens (namely CD2, CD3, CD4, CD8, CD16, CD20 and CD57) and flow cytometry in lysed peripheral blood of normal neonates (1-3 days old), 1-6 month, 7-12 month, 1-2 year old babies and 3-5 year, 6-10 year old children and young people up to 17 years of age. The results confirm the lymphocytosis at birth and at later stages of life and indicate that major changes in the distribution of lymphocyte subsets occur during the first two years of life; namely we have observed sharp increase of circulating B lymphocytes and prevalence of CD4+ T lymphocytes with high CD4/CD8 ratios in babies up to two years of age, compared to the values observed in normal adults. Very few CD8+ CD57+ lymphocytes were present at birth; cells bearing this phenotype appeared later in life. Lymphocytes expressing the CD16 antigen were already present in newborns. The authors discuss the functional meanings of the age-related changes observed in the distribution and in the numbers of circulating lymphocytes. The presented data represent valuable normal ranges of lymphocyte subsets to compare with values observed in sick babies or children.