Characterization of antigens recognized by natural killer cells in cell-culture supernatants

Inhibitors of natural killer (NK) cell activity in cell-culture supernatants, believed to be antigens recognized by NK cells, were defined by their ability to inhibit NK cells in 51Cr-release cytotoxic assays. Supernatants from cultures of melanoma cells and Chang cells were used as the source of the antigen. Partial characterization by a number of sequential separation procedures suggested that the antigens were glycoproteins in the size range 120-140,000 daltons which had affinity for both concanavalin A and wheat germ lectin. Inhibitory activity was destroyed by trypsin digestion, but was resistant to neuraminidase and a number of physical procedures. Addition of supernatants to NK assays against a number of different target cells indicated that inhibition was restricted to certain target cells. This indicated that the inhibition of NK cells was not non-specific, and that the antigens were not expressed on all target cells. These studies provide a basis for further analysis of antigens recognized by NK cells, and allow investigation of their role in vivo in tumour-bearing hosts.