• flow cytometry;
  • immunophenotyping;
  • lymphocyte subsets

In an attempt to establish the reference ranges for lymphocyte subsets in children, the distribution of lymphocyte population-bearing surface markers such as CD3 (T cells), CD 19 (B cells), CD4 (T helper/inducer cells), CD8 (T suppressor/cytotoxic cells), and CD 16 and/or CD56 on CD3” cells (NK cells) has been studied among healthy Saudi Arabian infants and children. Normal adult blood donors were used for comparison. Anticoagulat-ed peripheral blood was stained with monoclonal antibodies and the lymphocytes were analyzed by flow cytometry for the expression of the above markers. Absolute and percentage values for most lymphocyte populations differed substantially not only between children and adults but also among children from different age groups. Absolute numbers of all the lymphocyte subsets decreased with age from 1 month to 13 years; the median value declined from 4.1 to 1.9 (T cells), 1.6 to 0.6 (B cells), 0.5 to 0.3 (NK cells), 2.7 to 1.0 (CD4+ T cells) and 1.5 to 0.8 times 103 cells/mm3 (CD8+ T cells). HLA-DR+ T cell counts changed significantly from 0.3 to 0.2 times 103cells/mm3 during the same age period. In contrast, the lymphocyte percentage increased in all the subsets except B cells and CD4+ T cells with time. The percentage values increased from 66 to 74 (T cells), 8 to 11 (NK cells), 23 to 39 (CD8+ T cells) and 4 to 9 (HLA-DR+ T cells). The values changed from 24 to 12 and 46 to 39 for B cells and CD4+ T cells, respectively, with age from 1 month to 13 years. The variations in CD4+ and CD8+ T cells resulted in a decrease in CD4+/CD8+ ratio from 2.0 to 1.1 with age. These data should be useful as reference values for lymphocyte subsets in various diseases of infants and children.