Suppressor Activity of T Lymphocytes from Infants Assessed by Co-Culture with Unfractionated Adult Lymphocytes in the Pokeweed Mitogen System

T lymphocytes were isolated by E rosette sedimentation from cord blood lymphocytes and from the peripheral blood lymphocytes of healthy children of various ages. Fc(IgG) receptor-bearing T lymphocytes were enumerated by rosette formation with ox erythrocytes coated by IgG fraction of rabbit antisera. Relative proportions of Fc(IgG) receptor-bearing T cells in T cell-enriched populations of cord blood and newborn infants were higher than those in later life and decreased to near healthy adult levels by 3 months of age. Only a few of lymphocytes in cord blood were differentiated into immunoglobulin(Ig)-producing cells in vitro by poke-weed mitogen-(PWM) stimulation. The generation of Ig-producing cells in peripheral blood lymphocytes increased with age and reached about half the adult mean at 3 years of age. The suppressor activity of T lymphocytes were evaluated by co-culture with unfractionated adult lymphocytes on PWM-system. The PWM-induced differentiation of adult B lymphocytes into Ig-producing cells was markedly suppressed by the addition of T lymphocytes from cord blood. The suppressor activity of cord T lymphocytes was dose dependent to some extent and appeared to be equally effective on the generation of Ig-producing cells of three major classes, IgG, IgA, and IgM. Such suppressor activity of T lymphocytes was observed throughout infancy and gradually decreased with age. At 2 years of age or later, the suppressor activity of T lymphocytes, as evaluated by co-culture with adult lymphocytes, was not consistently demonstrated.