Target-induced anergy of natural killer cytotoxic function is restricted to the NK-target conjugate subset.

This study examined the characteristics of functional anergy of natural killer cells (NK) following their interaction with target cells. Purified NK cells were cocultured with K562 for 15 min or 4 hr to allow for binding of targets to NK cells. The resulting NK-target conjugates were then dissociated by EDTA, and the unbound NK cells were separated from the targets by flow cytometry and cell sorting. Compared to untreated NK cells, the K562-dissociated NK cells were inhibited for cytotoxic function as assessed by the 51Cr release assay and by the single killer frequency assay and also responded poorly following activation by IL-2 or IFN-alpha. The inactivated NK cells had a diminished ability to reform conjugates with the target cells. Following cell sorting of the NK subsets, the conjugate subset had the least cytotoxic activity when compared to both the free NK subset or the unfractionated NK population. The IL-2 response observed with the unfractionated anergic NK cells was found to be due to the activation of the NK free cell subset while the conjugate subset was poorly responsive to IL-2. The cell surface CD16, CD2, and CD56 antigen expression was downmodulated in the conjugate subset but not in the free cells. However, the CD69 surface expression was significantly upregulated on the surface of the NK conjugate subset and was potentiated following treatment with IFN-alpha and IL-2. These results demonstrate that target-mediated anergy of NK cells is restricted to the NK-target conjugate subset while sparing the remaining free cell subset. Further, the findings demonstrate that the anergic NK cells express the phenotype CD16dimCD2dimCD56dimCD69brightCD11bbright.