Describe two distinct mechanisms by which naive CD8 T cells can be activated

Question

What will be an ideal response?

Answer 1

(i) Virus-infected dendritic cells provide adequate co-stimulation (via B7) and can activate CD8 T cells directly without the involvement of CD4 T cells. CD8 T cells receive signal 1 (MHC:T-cell receptor) and signal 2 (B7:CD28), synthesize IL-2 and the high-affinity IL-2 receptor, and proliferate and differentiate into cytotoxic T cells.
(ii) In some cases, virus-infected dendritic cells cannot on their own fully activate naive CD8 T cells but the CD8 T cell begins to express IL-2 receptors. With the provision of help from effector CD4 T cells in the form of IL-2 secretion, these CD8 T cells are fully activated. For this to occur, simultaneous interaction with both the naive CD8 T cell and the effector CD4 T cell must occur.