Suppressor cells of natural killer activity in normal and tumor-bearing individuals

Suppressor cells of the human natural killer activity were found in normal peripheral blood and in the blood of patients with untreated primary carcinomas. When lymphocytes from healthy donors were fractionated by Percoll density gradient centrifugation, small lymphocytic, high-density cells inhibited K562 killing in 9/55 consecutively tested cases, and lymphocytes from tumor patients in 1/25 consecutively tested cases. Further fractionation of the suppressor cells was achieved by EA rosetting, since strong suppressor cell activity was seen in the population of cells forming EA rosettes with antibody-coated erythrocytes, whereas the nonrosette-forming cells did not generally suppress. Out of the 33 further fractionated samples from healthy donors, 20 rosette-forming lymphocytic cell fractions exerted strong suppression and out of the 7 samples from tumor patients 2 exerted suppression after EA rosetting. The increase in suppression after EA rosetting was partly due to enrichment of suppressor cells, and partly due to activation of FcR-positive suppressor cells after exposure to immune complexes. The involvement of soluble immune complexes, possibly retained on the suppressor cell surface, was ruled out by the following criteria (i) trypsin and pronase treatment of suppressor cells did not inhibit suppression, (ii) protein A had no effect on the level suppression, and (iii) suppression was also seen with cells which had not been exposed to immune complexes.