Umbilical-cord-blood-derived suppressor cells of the human natural killer cell activity are inhibited by interferon.

The natural killer (NK) activity of umbilical-cord-derived lymphocytes was studied. The general level of activity was lower than with adult lymphocytes against K-562 cells and fetal fibroblasts. The activity could be boosted by interferon pretreatment of effect or cells, fractionated with Percoll density gradient centrifugation, and the suppressive activity of different fractions was tested on highly enriched adult buffy-coat-derived NK cells. Allogeneic adult NK cell activity could be inhibited in 9 of 20 cases tested with small and medium-sized T lymphocytes (Percoll fractions 4-5) from the umbilical cord. The suppressive capacity was further enriched in fractions forming rosettes (RFC) with antibody-coated human erythrocytes (EA). Such EA-RFC of percoll fraction 4-5 from umbilical cord exerted a strong suppressive activity in each case tested. Pretreatment of EA-RFC with interferon regularly abolished the suppressive effect. We conclude that there are Fc-receptor-positive small/medium-sized T lymphocytes in the umbilical cord blood which can efficiency suppress the cytotoxic activity of NK cells and that the suppressive activity can be abolished by interferon pretreatment of the suppressor cells.