Question

Regarding T cell and antigen presenting cell (APC) interactions, name a pair of proteins that mediate the initial interaction between these cells.  In your answer, indicate which protein is expressed by the T cell and which protein is expressed by the APC.

Answer Part b i and ii.

The interaction between these proteins becomes stabilized in some cases, thereby prolonging the cell-cell contact.

i.  What event triggers the interaction between these proteins to become stabilized?

ii. How does the interaction between these proteins become stabilized i.e. what’s the mechanism?

This is how the question was asked... im not sure how he wants it exactly but anything will help.

Answer 1

i)

The T cell receptor (TCR) on both CD4+ helper T cells and CD8+ cytotoxic T cells binds to the antigen on the surface of the APC. This triggers initial activation of the T cells. The CD4 and CD8 molecules then bind to the MHC molecule too, stabilising the whole structure.

ii)

In addition to TCR binding to antigen-loaded MHC, both helper T cells and cytotoxic T cells require a number of secondary signals to become activated and respond to the threat. In the case of helper T cells, the first of these is provided by CD28. This molecule on the T cell binds to one of two molecules on the APC – B7.1 (CD80) or B7.2 (CD86) – and initiates T-cell proliferation.

This process leads to the production of many millions of T cells that recognise the antigen. In order to control the response, stimulation of CD28 by B7 induces the production of CTLA-4 (CD152). This molecule competes with CD28 for B7 and so reduces activation signals to the T cell and winds down the immune response. Cytotoxic T cells are less reliant on CD28 for activation but do require signals from other co-stimulatory molecules such as CD70 and 4-1BB (CD137).