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 lymphocyte subsets obtained from cord blood and on peripheral blood lymphocytes (PBL) from both term and preterm neonates. In some experiments, expression of the same antigen has also been evaluated after in vitro 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 CD8+ CBL as compared with the same subsets evaluated in adult individuals. Moreover, at variance with adult PBL, the great majority of CBL displayed a low level of fluorescence when stained with UCHL1 (CD45R0-specific monoclonal antibody), and both PHA and allogeneic stimuli were able to strongly increase the expression of the CD45R0 molecule on CBL. The percentage of CD45R0+ PBL obtained from both term and preterm neonates on the 1st day of life was comparable to that of CBL, however the expression of this molecule increases remarkably within a few days in the majority of term neonates, while it seems to take more time for the antigen to be fully expressed in preterm infants.