Enriched natural killing and antibody-dependent cellular cytotoxicity in lymphocyte populations adherent to tumor cell monolayers.

We have previously shown that human peripheral blood lymphocytes that do not adhere to natural killer (NK)-sensitive target cell monolayers are at least partially depleted of NK activity. To demonstrate directly that NK effector cells adhere to the monolayers, we have now recovered the adherent populations by treatment with ethylenediaminetetraacetic acid. When tested immediately after isolation, these adherent populations show NK activity that is intermediate between that of the nonadherent and control cells. When antibody-dependent cellular cytotoxicity is tested concomitantly, the adherent fractions are consistently found to be enriched relative to control, unfractionated lymphocytes. In further studies, control populations and fractions nonadherent and adherent to HSB monolayers are incubated overnight at 37 degrees C and then tested for NK activity. We find that the adherent fractions are selectively enhanced in activity, causing the NK activity of the adherent fractions to exceed that of control populations. The possible involvement of interferon in the augmentation of NK activity is considered.