38 FAILURE OF INHIBITION OF LYMPHOCYTE PROLIFERATION BY HUMAN NEWBORN MONOCYTES CORRELATED WITH A LOW PGE2 SECRETION

Abstract

We showed that an excess of autologous or allogeneic monocytes, isolated from adult blood, added to mitogen or antigen-induced lymphocyte cultures inhibited their proliferative responses. Similarly, adult monocytes reduced the generation of Pokeweed mitogen-induced plasma cells. These suppressive effects were, both, mostly reverted by adjunction of Indomethacin (5.10−7M). In contrast, newborn (NB) monocytes did not exert any effect on proliferation and generation of plasma cells. Adherent NB monocytes were shown to secrete 10 times less prostaglandin E2 (PGE2) during a 24hrs incubation than adult monocytes. (2.300 vs 24 000 pg/m/106 monocytes). After activation by zymosan, NB monocytes secreted 6 to 10 times more PGE2. The same effect was obtained by incubation in supernatant of allogeneic leukocyte cultures and NB monocytes became able to suppress T and B in vitro functions. Also monocytes from late pregnant women did not suppress T lymphocyte proliferation. Our observations suggest that absence of suppressive effect of NB monocytes is due to an inhibition of PGE2 secretion rather than to an intrinsic immaturity. This phenomenon, which seems correlated with an excess of suppressor activity exerted by NB T lymphocytes on B lymphocyte maturation might play a role on immune responses in neonatal period.