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Flashcards in TCRs & Antigen Presentation Deck (13)
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T-cell receptor

The TCR binds linear arrays of amino acids

It does not recognise native antigen

There are two types of TCR



TCR signalling

The TCR itself does not carry out any signalling

Instead, it uses CD3; a molecule of 6 polypeptides, each with one ITAM

CD4 and CD8 also play a role in T-cell signalling


CD8 T-cells

Recognise MHC class I molecules


CD4 T-cells

Recognise MHC class II molecules


T-cell activation

T-cell activation occurs when the TCR interacts with the MHC/antigen complex

CD4/ CD8 then join this complex

CD3 then initiates intracellular signalling


Antigen processing

The antigen fragments are then loaded into an MHC complex


MHC class I

Found on all nucleated cells and platelets

Involved in antigen recognition of virally infected cells or altered self-material

Present to CD8 T-cells


MHC Class II

Found on professional antigen presenting cells

Present to CD4 T-cells


Dendritic cells

Dendritic cells are a key link between innate and adaptive immunity

When they encounter antigen, they translocate to the lymph nodes where they activate T-cells


MHC Class I - loading mechanism

Carry out the endogenous pathway

Antigens come from within the cell

They are processed by the proteosome and then imported into the ER by TAP proteins

The antigen fragments are then loaded into the MHC with the help of calnexin and ERp57


MHC Class II - loading mechanism

Carry out the exogenous pathway

Antigens come from outside the cell

MHC is produced in the ER and packed into vesicles; invariant chain (Li) blocks the binding site

The vesicles fuse with endocytosed vesicles containing antigen

Li is partially degraded, leaving behind CLIP which is then displaced by the peptide with the help of DM


Non-classical T-cell activation

y/d T-cells make up 5% of all T-cells in the body

They are found in epithelial-rich tissues

They recognise antigen presented by CD1

Function unknown



Proteins secreted by extremely virulent bacteria and viruses

Able to bypass normal antigen recognition and bind non-variable regions of the TCR, causing activation

High effective even at low doses