Immunosuppressive activity of cord blood leukocytes.

The in vitro effects of cord blood cells from term and preterm infants on cell-mediated immune responses by adult lymphocytes were studied. The experiments showed that cord blood cells were potent suppressors of antigen- and mitogen-induced proliferation of adult T cells. In contrast to the previously reported observations with adult suppressor cells, the cord blood cells did not require mitogenic activation to exert their suppressive activity. It was also found that a similar, if not identical, suppressive activity was released into the fluid phase when cord blood cells were placed in tissue culture for three to five days. Studies with subpopulations of cord blood cells showed that the suppressive factor was released from rosette-forming T lymphocytes, but not from cell populations that were depleted of T cells. In addition, the production of and the action of the soluble suppressive factor was inhibited by indomethacin.