| Criteria | Marks |
|---|
| Describes similarities and differences between natural killer cells and cytotoxic T cells. | 4 |
| Outlines similarities and differences between these cells. | 3 |
| Describes similarities or differences between these cells. | 2 |
| Outlines similarities or differences between these cells. | 1 |
Sample answer:
Natural killer cells are part of the innate/second line of defence. They do not require antigen presentation to be activated. They act early in the immune response / rapid response. NK cells respond quickly to infections, providing an immediate defense during the early stages of viral invasion, before the adaptive immune response fully takes effect. They are non-specific. By eliminating infected cells early in the infection, NK cells help limit viral replication and prevent the spread of the virus to neighboring cells.
Cytotoxic T cells are part of the adaptive/3rd line of defence. They act later in the immune response. They are specific/targeted to the pathogen. Their antigen receptors bind specifically with the antigen displayed on the infected cell.
Both cells recognise virally infected cells displaying antigen on their MHC-I marker, resulting in cell death or apoptosis.
Both release granules containing perforin and granzymes. These substances create pores in the target cell's membrane, leading to cell death.