Expression of the costimulator molecules, CD40 and CD154, on lymphocytes from neonates and young children

Differential expression of the costimulator molecules CD40 and CD154 on neo natal lymphocytes may be one explanation for limited T-dependent antibody r esponses in human neonates. CD40 was expressed at similar levels on resting B cells from adults, young children (2-20 months of age) or cord blood. CD 40 expression was higher on cord blood B cells compared to adult B cells af ter stimulation with PMA and ionomycin, but similar on adult and cord blood B cells activated by CD3-stimulated T cells. In contrast to previous repor ts, cord blood T cells stimulated with PMA and ionomycin expressed adult le vels of CD154 initially, but this expression was more transient on cord blo od T cells. When adult and cord blood mononuclear cells were stimulated wit h CD3 mAb, T cells from some card blood specimens showed different kinetics of CD154 expression compared with adult T cells. However some cord blood s pecimens showed adult patterns of T cell CD154 expression. When mononuclear cells were depleted of B cells and monocytes prior co stimulation with CD3 mAb, the MFI and percentage of T cells expressing CD154 increased, with ad ult and cord T cells showing similar patterns of expression. These results show some differences in expression of CD40 and CD154 between neonatal and adult lymphocytes, bur do nor directly account for the relative deficiencie s of humoral immunity in neonates. (C) American Society for Histocompatibil ity and Immunogenetics, 2000. Published by Elsevier Science Inc.