Natural cytotoxicity in the neonate: high levels of lymphokine activated killer (LAK) activity.

In 28 healthy full-term newborns the percentage of circulating cells expressing the Leu7 antigen, the marker of natural killer (NK) cells, was significantly lower than in healthy adults. However, newborns and adults did not differ with regard to the percentage of cells reacting with the Leulla, Leullc and TEC NK-1, monoclonal antibodies directed against the IgG Fc receptor of killer cells. Spontaneous NK activity of neonatal cells was profoundly reduced compared to the adult. In contrast, antibody dependent cellular cytotoxicity and NK-like activity generated in mixed lymphocyte cultures were similar in the two groups and lymphokine-activated killer cell (LAK) activity was high in the neonate. Natural killing is thought to play an important role in antiviral immunity since the neonate has a deficient capacity to deal with viral infections. Consequently, the present data indicate either that spontaneous NK is the most informative in vitro measure of newborn natural cytotoxicity in vivo, or, alternatively, that natural killing is not as important in antiviral immunity as previously suggeste

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

In vivo activated cord blood lymphocytes express high affinity interleukin-2 receptor: evaluation of their responsiveness to in vitro stimulation with recombinant interleukin-2.

We report the phenotypical and functional characterization of a cord blood mononuclear lymphocyte subset (CBMC) which expresses the p55 chain of interleukin-2 receptor (IL-2R, CD25). The great majority of CD25-positive CBMC are activated CD3-positive T lymphocytes in that most of them are HLA-DR-positive, coexpress both CD4 and CD8 antigens and at least a part of them display high affinity IL-2R. In keeping with the expression of both chains of IL-2R (p55 and p75), enriched CD25-positive CBMC are able to display strong IL-2-induced proliferation and lymphokine-activated killing activity. The percentage of CD25-positive cells is higher in cord blood than in adult peripheral blood and their presence could be peculiarly important in the neonatal period, when specific T-cell-mediated immune responses are still on their way to full maturation

Colostral T lymphocytes detected by intracytoplasmic and membrane markers.

Colostral lymphocytes were studied using two established T-cell markers: intracytoplasmic alpha-naphtyl-acetate esterase (ANAE) staining and membrane receptors for sheep erythrocytes (E rosettes). ANAE staining allowed counting and identification of T-cell subsets independently of the status of membrane structures and receptors frequently altered in colostral cells. The fact that a sizeable number of colostral lymphocytes had the same phenotype as the majority of mature circulating peripheral blood lymphocytes supports the hypothesis that colostral lymphocytes may play a role in protecting neonates against infections, in transferring immune information to the newborn, or in modulating the immune response via release of soluble factors. A considerable percentage of colostral T lymphocytes are ANAE-negative. This phenotype is similar to that observed among thymocytes