Phenotypic immaturity of T and B lymphocytes in cord blood of full-term normal neonates. Analysis of cell surface markers by using conventional techniques and monoclonal antibodies.

We examined mononuclear cell subsets in cord blood of normal newborns by surface marker analysis. The percentages of T lymphocytes (E-rosetting and T3+ cells) were lower in cord blood than in peripheral blood (PB) from adults, while the percentage and absolute number of T6+ cells were higher in cord blood. As the sum of T4+ and T8+ cells exceeded the values of E-rosetting lymphocytes in cord blood, we suggest that immature lymphocytes with the phenotype of 'common' thymocytes (T6+, T4+, T8+) are present in cord blood of full-term newborns. Higher percentage and absolute number of B lymphocytes were detected in cord blood. More than 50% of B cells in cord blood formed rosettes with mouse erythrocytes, a surface marker of functional immaturity. Finally, cells bearing receptors for IgG-Fc fragments or C3 and expressing Ia-like and M1 antigens were uniformly increased in cord blood, suggesting higher percentages of cells of the monocytic lineage.