1. ANTIGEN
PROCESSING AND
PRESENTATION
Dr. Ahmed M. Salih

5.  Professional APC
 Macrophages, dendritic cells, and B cells,
which can express MHC class II molecules.
 Other cell type capable of expressing MHC
class II molecules
eg. Endothelial cells, EC
Fibroblasts
Activated T cell

6. 1. Binding and uptake of antigen
 depends on the physical state of the antigen and
the cell type involved.
2. Antigen processing
 MHC class I processing pathway
 MHC class II processing pathway
3. Antigen presentation
Antigen processing

7. 1 Binding and uptake of antigen
 exogenous antigens
 Bacteria, cells and soluble proteins
 processed by APC
 endogenous antigens
 Produced within the cells, Such as viral proteins or
tumor proteins
 processed by host cell

9. Uptake antigen by immature DC
 Pinocytosis
 Liquid or small granule
 Receptor-mediated endocytosis
 effective
 selective
 saturated
 FCR, R
 Phagocytosis
 Large molecular or microbe

10.  Phagocytosis
 Large solid or molecular complex, such as
bacteria, fragment of cells, etc.
 Phagecyte (mf, granulocyte)
 Pinocytosis
 Receptor-mediated pinocytosis
 Endocytosis
 Low levels of particulate or soluble antigens
 exocytosis
Uptake antigen by MPC

11.  nonspecifically engulfed
 BCR-mediated
Uptake antigen by B cells

12. 2 Antigen processing
 Degradation of externally- or internally- derived
antigen into short peptide sequences
 Association of the peptide with MHC molecules

13. Two antigen-processing pathways
MHC class I MHC class II
Major antigen
sources
endogenous
antigen
exogenous antigen
Processing
machinery
proteasome lysosomal enzymes
Cell type where
active
all nucleated cells professional APCs
Site of antigen-
MHC binding
endoplasmic
reticulum
lysosome and
endosome
MHC utilized MHC class I MHC class II
Presents to CD8+ T cell (Tc) CD4+ T cells (Th)

14. MHC class I
processing pathway

15. MHC class I processing pathway
Antigenic protein - proteosome - peptide fragment
released into cytosol - binds to TAP protein
moves to endoplasmic reticulum(ER)
Newly synthesized Class I a chain and b2
microglobulin - move to ER calnexin binds to a
chain peptide fragment and b2m bind to a chain
release of a chain from calnexin complex moves
to Golgi apparatus glycosylation in Golgi
apparatus secretory vesicle plasma membrane

21. proteasome
 LMP, low molecular weight polypeptide or large
multifunctional protease
 Structure:
 20S - 26S
 Function:
 Degradation of protein

23. 26S protease cmplex
20S proteasome
twin 19S cops

24. TAP, transporter associated with
antigen processing
 structure:
 TAP-1 and TAP-2
 function:
 transports small peptides (8-13 aa) to the ER

25. Molecular chaperones: calnexin,
calreticulin,tapasin

26. MHC class II
processing pathway

28.  Antigenic protein - endosome/lysosome
peptide fragment
 Newly synthesized class II molecules move to
ER and associate with invariant chain protein
molecule move to Golgi apparatus move to
endosomes/lysosomes release of invariant
chain from class II molecule class II binds
antigenic peptide fragment transport to cell
surface
MHC class II processing
pathway

29. Endosome & lysosome
 acidic protease & lysosome enzymes
 Function
 Degrade protein into peptide fragments (10-30 aa)

30. invariant chain, Ii
 Function
 Promote the formation of MHC II a b dimer
 Directs the movement of newly synthesized
class II molecules into the Golgi and then the
late endocytic compartment of the cell
 Prevent the binding of antigenic peptides to
class II molecules, at least until the class II
molecule reaches the late endocytic
compartment

32. 3 Antigen presentation
 Antigen presentation
 The activation of T cells via T cell receptors, which
specifically recognize antigenic peptide in association
with either MHC class I or II molecules on the
surface of APC.

34. Thank You