NK‐patterned binding expressed by non‐NK mouse leukocytes

Previous studies demonstrated that NK‐cell‐enriched spleen cells bind to sensitive but not to resistant mouse lymphoma targets, measured by a single‐cell target binding assay. In the present report we further analyzed this “NK‐patterned” binding using effector cells with high, low or no NK activity. In agreement with previous results, nylon‐wool‐passed spleen cells as well as a cloned cytotoxic cell line with NK activity bound tumor targets largely according to their NK sensitivity; NK‐sensitive tumors had a higher frequency of binders than the more resistant ones. The correlation coefficient relating the percentage target binding cells (TBC) for each tumor with the ability of the same tumor to inhibit lysis in cold target competition assays was consistently higher than that relating percentage TBC with direct NK lysis. A non‐lytic variant of the cloned cytotoxic cell line had a binding pattern identical to that of the lytic line, demonstrating that “NK‐patterned” binding occurred in the absence of lysis. Thymocytes, which are totally devoid of NK activity, also bound preferentially NK‐sensitive targets, and their binding was decreased after trypsin treatment or in the presence of EDTA. Peritoneal macrophages also showed “NK‐patterned” binding, thus demonstrating that this was not restricted to cells in the T‐cell lineage. Variants from a mouse lymphoma selected for decreased NK sensitivity bound a lower frequency of NK‐active (nylon‐wool‐passed spleen cells) and inactive cells (thymocytes, peritoneal macrophages). This study therefore showed that the membrane property conferring NK‐binding selectivity exists on several types of non‐NK leukocytes.