Ontogeny and postnatal persistence of a strong suppressor activity in man

We report here on the ontogeny and postnatal persistence of an inhibited human immune response in which lymphocytes from human newborns strongly suppress the proliferation of adults' lymphocytes stimulated by phytohemagglutinin (PHA) or alloantigens in vitro. For this research we used a 2-way mixed lymphocyte culture (MLC) supplemented with PHA, with sex chromosomes acting as markers for dividing male and female cells, or alternatively a double chamber system. The proliferation of maternal lymphocytes was significantly suppressed by fetal lymphoid cells from the liver as early as the 8th week of gestation and by those from fetal blood at the 14th week or later during gestation. This strong suppressor activity persisted in 11-mo-old infants but usually disappeared after that time.