Question

NK cells arise from the adaptive linage, but play a key role in innate immune responses to viral infection.

a. What are the three different ways inflammatory cytokines make NK cells cytotoxic?
b. What molecule does CD94:NKG2A recognize on target cells? How does this act as a go, no-go signal for NK cells?

Answer 1

NK cells can become cytotoxic through various mechanisms induced by inflammatory cytokines. CD94:NKG2A on NK cells recognizes HLA-E on target cells and acts as a go, no-go signal.

Step-by-step explanation:

NK cells arise from the innate immune system but play a key role in innate immune responses to viral infection. Inflammatory cytokines can make NK cells cytotoxic through three different ways:

1. By inducing the expression of the Fas ligand on the surface of NK cells, which can bind to the Fas molecule on the target cell, triggering apoptosis.
2. By secreting perforin, a protein that creates pores in the target cell's membrane, allowing entry of other cytotoxic molecules into the cell.
3. By releasing granzymes, proteases that can enter the target cell through the pores created by perforin and induce apoptosis.

CD94:NKG2A is a receptor on the surface of NK cells that recognizes HLA-E, a molecule expressed by healthy cells. When CD94:NKG2A binds to HLA-E, it acts as a go signal, signaling the NK cell not to kill the healthy cell. However, when the expression of HLA-E is downregulated, for example, during viral infection, CD94:NKG2A cannot bind to it, indicating a no-go signal and allowing NK cells to kill the infected cell.