EXPRESSION OF CD45R0 ANTIGEN ON THE SURFACE OF RESTING AND ACTIVATED NEONATAL T-LYMPHOCYTE SUBSETS

Expression of CD45R0 antigen has been evaluated on the surface of T ly mphocyte subsets obtained from cord blood and on peripheral blood lymp hocytes (PBL) from both term and preterm neonates. In some experiments , expression of the same antigen has also been evaluated after in vitr o activation of cord blood lymphocytes (CBL) with phytohemagglutinin ( PHA) or in mixed lymphocyte culture. The CD45R0 molecule was found to be present on a significantly lower percentage of CD3+, CD4+ and CD8CBL as compared with the same subsets evaluated in adult individuals. Moreover, at variance with adult PBL, the great majority of CBL displa yed a low level of fluorescence when stained with UCHL1 (CD45R0-specif ic monoclonal antibody), and both PHA and allogeneic stimuli were able to strongly increase the expression of the CD45R0 molecule on CBL. Th e percentage of CD45R0+ PBL obtained from both term and preterm neonat es on the Ist day of life was comparable to that of CBL, however the e xpression of this molecule increases remarkably within a few days in t he majority of term neonates, while it seems to take more time for the antigen to be fully expressed in preterm infants.