Which of the following are cells of the adaptive immune system?

The story behind the answer

Cytotoxic T cells are adaptive immune cells because they use a specific T-cell receptor (TCR) to recognize peptide antigens presented on MHC I molecules and then kill infected or cancerous cells using perforin and granzymes. They undergo clonal expansion and form memory—hallmarks of adaptive immunity. In contrast, natural killer (NK) cells are innate lymphocytes that don’t require antigen-specific priming, dendritic cells are innate antigen-presenting sentinels that activate T cells, and “white blood cells” is a broad category that spans both innate and adaptive cells.

Remember it this way: T for Targeted—Cytotoxic T cells are trained, specific assassins; NK cells are Natural and nonspecific. CD8+ pairs with MHC I to clear intracellular threats (viruses and tumor cells). This specificity and memory are key reasons vaccines can generate durable T-cell responses.