T and B lymphocytes in the ontogenetic development of man.

Cord blood lymphocytes of premature and mature fetuses and peripheral blood of infants and adults were studied by rosette techniques and membrane immunofluorescence. Percentage of lymphocytes carrying surface immunoglobulins, receptors for complement and receptors for uncoated sheep erythrocytes or receptors for Fc IgG was determined. T lymphocyte receptors were found to appear later in ontogeny than the receptors typical of B lymphocytes. Receptors for Fc IgG were the earliest to appear: already in premature fetuses the percentage of lymphocytes resembled the one seen in healthy adults. However, the absolute number of T cells increased during development of fetuses and infants and slightly decreased in adults. On the other hand, the absolute number of B lymphocytes were highest in mature fetuses and decreased in subsequent age groups. In the course of human ontogeny a progressive increase was found in lymphocytes carrying full sets of T or B lymphocyte receptors, paralleled by a corresponding decrease in mean values of "null" lymphocytes free of detectable receptors.