Spontaneous IgM Autoantibody Production In Vitro by B Lymphocytes of Normal Human Neonates

Human neonate B lymphocytes display unique phenotypic and functional characteristics: in addition to CD1c antigens, CD5+ and CD5‐ subsets both express activation markers such as CD23 and Bac‐1. They proliferate strongly in the presence of various lymphokines (rIL‐2, rIL‐4, low molecular weight BCGF), but differentiate poorly in the presence of the same lymphokines, pokeweed mitogen and Epstein Barr virus. It has also been reported that human neonate B lymphocytes produce polyreactive autoantibodies after in vitro activation by Staphylococcus aureus Cowan I and transformation by Epstein Barr virus. We now show that, in the absence of in vitro stimulation, human neonate B lymphocytes produce polyreactive antibodies of the IgM isotype against several autoantigens. The B lymphocytes involved expressed membrane IgD, IgM, CD23 and CD11b molecules; CD5 expression was variable. This phenotype was consistently found on a minority of B lymphocytes and is similar to that of polyreactive autoantibody‐producing B cells in mice. We also found that autoantibody production in vitro could occur in the absence of any T helper effect The function of these autoantibodies is not clearly established, but their occurrence in a large proportion of human neonates strongly suggests that they play an important role in the development of the immune system. Copyright © 1992, Wiley Blackwell. All rights reserved