Analysis and enrichment of murine natural killer cells with the fluorescence-activated cell sorter.

The antiserum anti-NK 1.1 defines an alloantigen specific for natural killer (NK) cells on normal C57BL/6 spleen cells (SC). With complement this antiserum lysed an insignificant percentage of SC, yet could deplete SC suspensions of NK effector cells. The antiserum was also used in this study to indirectly fluorescein label NK cells. The anti-NK 1.1 serum labeled 10 to 15% of nonadherent, nylon column passed SC. The labeled cells were analyzed on the fluorescence-activated cell sorter (FACS), by using flow fluorometry, and were found to be small to medium-sized cells. SC were sorted on the FACS into labeled (NK-1+) and unlabeled (NK-1-) populations, and assayed for NK activity on YAC-1 cells. When compared with control SC, labeled NK-1+ cells were enriched 4- to 13-fold in lytic activity, whereas unlabeled NK-1- cells had little if any NK effector function. Thirty to 60% of the labeled SC adhered to YAC-1 tumor cells in a visual target binding cell assay. The percentage of lymphocytes in the sorted NK-1+ population that bound YAC-1 cells was over 3-fold greater than in unsorted control SC preparations. NK-1- sorted cells did not bind YAC-1 targets. In a preliminary experiment NK-1+ sorted SC inhibited outgrowth of YAC in A/J mice, whereas NK-1- sorted cells did not.