The cell populations mediating natural killing-(NK) and antibody-dependent cell-mediated cytotoxicity are only partially identical.

A cold target inhibition assay has been used to investigate the relationship between the effector cells responsible for NK and ADCC activity. Two models of ADCC have been studied in parallel with NK, one involving in vivo armed effector cells and the other involving normal effector spleen cells tested on antibody-precoated target cells. Bivalent effector cells active in ADCC and NK as well as monovalent NK cells and monovalent FcR-positive ADCC killer cells appear to exist concomitantly. However, the variability from experiment to experiment of the blocking efficiency displayed by the heterologous cold targets, suggests that the proportions of monovalent to bivalent cells may vary between batches of mice depending on their immunological status at the time of the test. This should be taken into careful consideration when interpreting the results of this type of investigation.