Phytohaemagglutinin-induced proliferation of human T lymphocytes: differences between neonate and adults in accessory cell requirements.

The accessory cell requirements of human neonatal T lymphocytes were compared with those of adult T lymphocytes in lectin-induced polyclonal activation. It was found that purified neonatal Esh rosette positive lymphocytes were not activated into a proliferative response by the lectin phytohaemagglutinin (PHA), by phorbol ester (TPA) or by conditioned medium containing T cell growth factor activity (TCGF-CM). A proliferative response to PHA was obtained in the presence of a suitable accessory cell (AC) such as the plastic adherent, monocyte enriched population or the sIg positive lymphocyte population, both of which were shown by cellular titrations to be equally effective. Optimal proliferative responses to PHA could also be obtained, in the absence of accessory cells, by addition of TPA or TCGF-CM. Neonatal T lymphocytes gave highly reproducible responses and this could be achieved effectively by simple separation procedures not involving further subfractionation of the responding Esh+ lymphocyte population. The exquisite accessory cell dependence of these cells demonstrated in this investigation provides a readily available human model system for the evaluation of the variables involved in T lymphocyte activation and a sensitive assay for measuring accessory cell activity.