Abstract
The sensitivity of colorectal tumors to NK‐cell‐mediated cytotoxicity and their expression of major histocompatibility complex (MHC) class‐I antigens were studied in an attempt to determine whether such antigens play a role in the susceptibility of colorectal tumors to NK‐cell lysis. In a rat colon‐carcinoma model, 2 clones differing in their sensitivity to NK‐cell‐mediated cytotoxicity were tested for class‐I expression; it was seen that the more sensitive cells (REGb) expressed less class‐I products than did the resistant cells (PROb). However, when MHC class‐I antigen expression was increased by IFN‐γ treatment, no change in NK‐cell lysis was found with the PROb cells, while an increase in cytotoxicity was obtained with the REGb cells. After in vivo or in vitro selection of NK‐resistant REGb cells, we observed in the selected cells an important decrease in RT‐I class‐I antigen expression. Fifteen different human colorectal cell lines were also studied for HLA class‐I expression and NK‐cell susceptibility, and no quantitative correlation between these 2 features was seen. However, cell lines which were deficient in HLA class‐I antigens were more sensitive than class‐I‐positive cells.