Natural killing (NK) potential of cord blood lymphocytes.

Different parameters of natural killing were evaluated in newborn cord lymphocytes using a 51Cr-release assay, a single cell cytotoxicity technique and an immuno-fluorescence method with HNK-1 monoclonal antibody. Cord blood lymphocytes expressed a positive natural killer (NK) activity although the level of this overall NK activity was lower than that of adult control (p less than 0.05). In neonates the number of cells bearing surface HNK-1 differentiation was very low (0.7 +/- 0.3). Contrary to this finding, newborns showed only a marginal decrease in the percentage of cells capable of recognizing and binding NK-sensitive target cells. However, the killing potential of these lymphocytes was impaired more profoundly (p less than 0.05) compared to adult controls. We conclude that in the neonate two distinct populations of effector cells participate in spontaneous killing. The first group is represented by classically defined NK cells (HNK-1 positive) while the second group represents. NK-like effector cells which lack the HNK-1 antigen. It seems that in newborns the latter type of cells represents the larger factor in spontaneous killing.