DR Medhat MRCP

Expression
Structure
MHC I
- In all nucleated cells (ie not on
RBCS) e.g
‣ T- cells
‣ B-cells
‣ Phagocytes & APCs
MHC II
- Only in APCs
‣ Macrophages
‣ Dendritic cells.
- Has one peptide limb bound to
phospholipid membrane of all
nucleated cells.
- Composed of 4 microglobulin
molecules one of them never
change its structure (βmicroglobulin)
& the upper 2
molec(α1 &α2) form a groove
acting as a cleft which is the
binding site of specific antigen.
- When an antigen is presented on
MHC I of certain cell , the
outcome is death of this cell as it
will be presented to cytotoxic T-
- Has 2 peptide limbs bound to
phospholipid membrane of
APCs .
- Composed of 4
microglobulins, one side
(α1&α2) & the other side
(β1&β2)
- Antigen-binding groove is
formed by α1 &β1
- When an antigen is presented
on MHC II , this will activate T-
helper cells (CD4+) which in
turn activates B-cell receptors.
cell (t-killer cells)(CD8+)
- Most commonly studied HLAs genes are :
‣ Class I : HLA-A , HLA-B, HLA-C
‣ Class II : HLA-DP, HLA-DQ , HLA-DR.
‣ Class III : they are not structurally or functionally related to class I&II and it
include genes of complement proteins & tumour necrosis factor.
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