Purified human NK cells do not function as accessory cells in T-cell proliferative responses.

In the present study we investigated the accessory function of natural killer (NK) cells in PHA, anti-CD3 (OKT3) and solid-phase-bound anti-CD3-induced T-cell proliferative responses, as well as in allogeneic mixed lymphocyte reaction (MLR). Although NK cell-enriched Percoll fraction cells showed accessory activity in all of the studied T-cell responses, the accessory function in anti-CD3 and allogenic responses were always found to be strictly dependent on the proportions of contaminating monocytes (Mo) and dendritic cells (DC). Purified CD16+ NK cells were totally incapable of inducing T-cell proliferation in anti-CD3, solid-phase-bound anti-CD3 and in allogeneic MLR responses, whereas these NK cells could support PHA-induced T-cell proliferation, although to a very low extent. Growing evidence suggests an inhibitory role of NK cells in various immune responses, but in the studied T-cell responses NK cells did not suppress either Mo or DC accessory ability.