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The natural killer cells or the NK cells identify and destroys the infected cells. These are the lymphocytes, which kill cells infected with tumor cells or viruses.

The normal self or the healthy cells are not identified or attacked by the NK cells.

The altered self or the non-self also known as the foreign proteins will be identified and attacked by the immune system of the body. The MHC II molecules are present primarily on the cells comprising non-self-proteins or antigens. The association of MHC II molecules takes place with the helper T cells to instigate the appropriate immune response that may comprise the inflammatory response.

Thus, the options a, c, and d are incorrect.

The NK cells determine the intracellular infections mainly from viruses, by the changed expression of MHC (major histocompatibility class) I molecules on the surfaces of the infected cells. Thus, the NK cells identify the missing self-pattern.

Hence, the correct answer is option b.