Final answer:
The statement that NK cell receptors must inhibit the NK cell from killing healthy self-cells is true. NK cells identify healthy cells through MHC I molecules which inhibit the NK cell's cytotoxic activity, while infected or tumor cells lacking MHC I are targeted for destruction.
Step-by-step explanation:
The statement that NK cell receptors must inhibit the NK cell from killing healthy self-cells is true. Natural killer (NK) cells play a critical role in the innate immune response by identifying and eliminating cells that have been infected by viruses or have become cancerous. They do this by recognizing the presence or absence of MHC I molecules on the surface of cells.
Healthy cells typically present MHC I molecules, and when NK cells encounter these cells, the interaction inhibits the killing sequence, allowing the healthy cell to survive. On the other hand, when a cell is infected or becomes a tumor cell, it may downregulate the expression of MHC I to evade the immune response. In such cases, the absence of MHC I signals to the NK cells that the cell is abnormal, triggering the release of cytotoxic granules containing perforin and granzymes that induce apoptosis in the target cell.