APCs and B Cells

[RosieBritney]

My question relates to the role of the B cell in role in being an APC.

I understand that dendritic cells are normally the main type of APC, and that the B7 protein has to be present on the APC in order to activate the T cell to become a helper T cell.

However when this activated t cell activates the B cell in order for the b cell to differentiate, it must bind to the B cells’ MHC class II and antigen combination on the b cell to ensure it is stimulating the right b cell.

But what I am confused about is, during this process of the b cell internalising antigen and presenting to the activated t cell, dose the B cell produce the B7 proteins as well?

Because surely if it did, the dentdritic cell would not be needed in the frist place to activate the t cell and only the b cell would have been needed, as the 2 signals needed by the T cell (antigen on MHCII and B7) would have been given by the B cell.

Therefore wouldn’t there be no use for the other apcs in this type of immune reponse, because the b cell can always provide both signals to activate the t cell?

When are B7 proteins expressed on APCs?

Can you also tell me whether I have got this concept right about whether B cells must internalise atigen via their BCR and express it via their MHCII in order for the T cells to respond to them?

 

Thankyou very much, I am so confused!!

[mavis]

Both dendritic cell and B cells have B7. B7-CD28 interaction is a co-stimulatory signal for the activation of Naive T cells instead of memory cells.

 

When antigen is internized into B cells, then expressed to MHC II and presented to Th cells. The B7-CD28 costimularoty signals are needed too.

 

http://www.ask4biology.com