Abstract
The functional capacity of human neonatal B lymphocytes has been investigated by in vitro methods using T lymphocyte‐dependent (pokeweed mitogen, PWM) and‐independent (Epstein‐Barr virus, EBV) polyclonal B cell activators. B cell activation of single cells was detected by class‐specific immunoglobulin (Ig) secretion using a reversed hemolytic plaque assay.
It was found that neonatal B cells were triggered to secretion of IgM by EBV, with a magnitude comparable to adult levels, but that, in contrast to B cells from adults, they did not secrete any IgG. Cord lymphocytes did not secrete Ig although they displayed a sizable DNA synthetic response to PWM. Using cell separation and coculture experiments, it was shown that (allogeneic) adult T lymphocytes could restore cord B cell responsiveness to PWM and that cord T lymphocytes could not cooperate with adult B cells.
In addition to this immaturity of cord T helper function for antibody synthesis, we found cells in the cord T cell‐enriched fraction which inhibited the polyclonal response of adult lymphocytes to both PWM and EBV. These lymphocytes suppressed adult B lymphocytes directly but appeared ineffective against neonatal B lymphocytes themselves. The nature of these suppressing cells and their possible role in the fetal/maternal relationship are a matter of speculation.