1. Antigen Processing and Presentation, Self MHC Restriction

2. What Does The B Cell Immunoglobulin (Ig) Receptor Recognize?
Proteins (conformational determinants, denatured or proteolyzed determinants)
Nucleic acids
Polysaccharides
Some lipids
Small chemicals (haptens)

3. Antigen Processing and Presentation
Fragmentation of protein into peptides
Association of peptide with an MHC molecule
Transport to cell surface for expression
Different cellular pathways for association of peptide with MHC class I and class II molecules

4. Proteasome degrades protein to protein moves peptide into ER
Class I MHC Pathway
Peptide is presented
by MHC-I to CD8
cytotoxic T cell
Viral protein is made
on cytoplasmic
ribosomes
Plasma membrane
Globular viral
protein - intact
Peptide passes
with MHC from Golgi
body to surface
Proteasome degrades protein to
peptides
rER
Peptide associates
with MHC-I complex
Peptide transporter
protein moves peptide into ER
MHC class I alpha
and beta proteins
are made on the rER
Golgi body
Peptide with MHC
goes to Golgi body

5. Class II MHC Pathway Plasma membrane Peptide MHC-II
complex is presented
to CD4 helper T cell
CD4 helper T cell
Globular protein
Plasma membrane
Fusion of endosome
and exocytic vesicle
Endosome
Endosome fuses with
plasma membrane
Endocytosis
Immunodominant
peptide binds
to class II MHC
Lysosome
Exocytic vesicle fuses
with endosome
releasing Ii from αβ dimer
Protein is processed to
peptides in endosome
or lysosome
Golgi
body
Class II MHC
Synthesis
3 chains: α,β and Ii α β Ii
Endoplasmic reticulum

7. Structure of Class I MHC
NH2
Alloantigenic
sites
CHO
COOH P α1 α2 α3 β2 OH
Plasma membrane
Disulfide bridge
Papain cleavage
Cytoplasm

8. Structure of Class II MHC
Plasma membrane
Cytoplasm
CHO
NH2
COOH α1 α2 β2 β1

9. Points Concerning Antigen Processing and Presentation
1. Location of pathogen
viruses in cytosol, MHC class I pathway, Tc response
extracellular bacteria, MHC class II pathway, TH2 response, Ab formation
intracellular bacteria, MHC class II pathway, TH1 response

10. Points Concerning Antigen Processing and Presentation
Peptides derived from both self and non-self proteins can associate with MHC class I and class II molecules.
Chemical nature of MHC groove determines which peptides it will bind.

11. Aspects of MHC
MHC molecules are membrane-bound. Recognition by T cells requires cell-cell contact.
Peptide from cytosol associates with class I MHC and is recognized by Tc cells. Peptide from vesicles associates with class II MHC and is recognized by TH cells.

12. Aspects of MHC (continued)
Although there is a high degree of polymorphism for a species, an individual has maximum of six different class I MHC products and only slightly more class II MHC products.
A peptide must associate with a given MHC of that individual, otherwise no immune response can occur. That is one level of control.

13. Aspects of MHC (continued)
Mature T cells must have a T cell receptor that recognizes the peptide associated with MHC. This is the second level of control.
Each MHC molecule has only one binding site. The different peptides a given MHC molecule can bind all types to the same site, but only one at a time.

14. Animation oh MHC I & II

15. Lymphatic Tissues Primary Lymph Tissues Secondary Lymph Tissues Bone
Marrow
Thymus Gland
Spleen
Lymph
Nodes
Bursa of
Fabrices
Bayer’s
Patches

17. Types of Abs
Against Same Ag
Allotype
Isotype
Idiotype
Different
Amimals
e.g.: Horse
to Human
Different classes
IgG, IgM, IgA
IgD, IgE
Different Variable
For the same Ag
On Same Class