first aid immuno picture confusing

[Fungi121]

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So this first aid picture is conflicting with other sources of information (lol the internet).

Do CD8 cells need to have the costimulatory B7-CD28 binding to get activated? If yes, this confuses me, because only APCs have B7, but all cells have MHC I. So once again, if you need B7, how could a normal cell (epithelial cell, for example) activate a CD8 cell?

 

[Alacran]

CD8 cells do need to have a co-stimulatory signal but it is not the B7-CD28.

B7-CD28 is used by APCs, which express MHC II also, as a secondary signal to activate CD4 pos T-cells. MHC I cells bind to CD-8 pos T-cells and the secondary signal comes from IL-2 released from CD4 Th1 cells. To help remember this, use CD4*B7 = CD28 and IL2 * CD4= CD8

 

[scoKraz4]

Naive CD8 cells can be activated in 3 ways:
1) CD8 interacts with dendritic cell (APC) via an MHC-I - TCR interaction and co-stimulation provided by B7-CD28 which is already highly expressed on the APC-->activated CD8 then secretes Il-2 which drives its own proliferation and differentiation
2) APC stimulates an effector CD4 cell that then activates the APC-->APC expresses B7 that can interact with CD28 on the CD8 cell
3) APC activates CD4 cell to make IL-2 and activates CD8 to express IL-2R-->IL-2 activates CD8 cell

So do they 100% need B7-CD28 interaction to be activated..no. But they can still be activated through that mechanism. So if an epithelial cell is infected, the CD8 will need the IL-2 to become activated.

 

[Fungi121]

ohhhh sweet It'll about the IL-2! Gotcha! Thanks guys