Analysis of natural killer (NK) cell activity and adhesion molecules on NK cells from umbilical cord blood

The activity of natural killer (NK) cells in human umbilical cord blood (CB) has been reported to be low, compared with that in adult peripheral blood (PB) in vitro . To examine the cause of this, after dividing the CD56(+) /CD3(-) cells in CB and PB into CD56(bright) and CD56(dim) NK cells, the NK cell activities and the expression of various surface antigens were assayed for each fraction. The NK cell activity of CD56(dim) NK cells in CB was significantly lower than that in PB (P = 0.0003), whereas, there was no significant difference between the NK cell activity of CD56(bright) NK cells in PB and CB. The expression levels of adhesion molecules (CD2, CD11a, CD18, DNAX accessory molecule-1), CD16, and CD57 for CD56(dim) NK cells in CB were significantly lower than those in PB, and approximately one-third of CB CD56(dim) NK cells were capable of forming conjugates with K562 cells, compared with PB CD56(dim) NK cells. Furthermore, the inhibition of both the NK cell activities and binding of CD56(dim) NK cells in PB and CB by monoclonal antibody against each of these adhesion molecules suggests that they play an important role in NK cell activity. These findings show that the low NK cell activity in CB is caused by the low NK cell activity of CD56(dim) NK cells and that the low expression level of adhesion molecules on CB CD56(dim) NK cells may contribute to this low NK cell activity.