Newborn T cell suppression: early appearance, maintenance in culture, and lack of growth factor suppression.

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Abstract
Human newborn T lymphocytes suppress the responses of adult lymphocytes to several stimuli, including the T dependent differentiation of adult B cells to plasma cells (PC) by pokeweed mitogen (PWM) stimulation. We tested blood from premature babies to show that the suppressor activity for PWM-induced B cell differentiation appeared by 26 weeks' gestation. Cord blood from full term babies delivered by Caesarean section also suppressed PC differentiation showing that maternal labor is not a prerequisite for suppression. Eleven percent of freshly isolated newborn T cells bore the putative suppressor phenotype OKT 8 and 81% had the putative helper phenotype OKT 4, so the increased suppression and diminished help of newborn T cells was not associated with an imbalance of phenotypic helper or suppressor cells. The function of newborn T cells was further investigated by establishing the cells in continuous culture with T cell growth factors. The polyclonal lines obtained suppressed adult PWM-induced PC differentiation and were inefficient helpers so their functional characteristics appear to be maintained in culture without changes in the balance of help and suppression. PHA-stimulated newborn lymphocytes were themselves efficient producers of T cell growth factors. We conclude that newborn T cells can suppress without lectin activation and that the suppressor activity that is found is a stable intrinsic characteristic of the cell.