MHCI and MHCII- role in antigen presentation

1. Sushma Ahirwar
Roll No.-Y17194425
Submitted By-
Dr. Deepali Jat
2019-20
DR.HARISINGH GOUR CENTRAL UNIVERSITY
SAGAR(M.P.)
TOPIC – Antigen processing and
presentation
Submitted To-
Class-B.Sc.B.Ed
semester-Vth
section-D1

2. CONTENT
 Basic Introduction to- Antigen, APCs and
MHC Complexes.
 What are antigen processing and
presentation?
 Types of pathways for antigen processing and
presentation
 Brief discussion of endogenous pathway or MHC
class I antigen presentation
 Brief discussion of exogenous pathway or MHC
class II presentation

3. Antigen Presenting cells(APCs)- These are specialized
cells,which includes macrophages,B cells and dendritic cells etc.
These cells are distinguished by following properties: APCs firstly
internalize the antigen by phagocytosis and display a part of that
antigen to TH-cells on their membrane ,bound to MHC molecule.
 Antigen- A toxin or other foreign substance which
induces an immune response in the body.Especially
the production of antibodies.
INTRODUCTION TO FOLLOWOING ASPECTS-
Macrophage Dendritic cell

8. Endogenous Pathway / Intracellular Pathway
OR
MHC Class I presentation
 In this pathway processing and presentation occur of
intracellular pathogen/antigen.
 Intracellular antigen- Antigen or pathogen which
replicate inside the host’s cells, Ex. viruses etc.
 This pathway is mediated by MHC Class I molecules. Before
initiation of pathway these MHC I molecule associated in ER
(endoplasmic reticulum). The heavy chain of MHC I is stabilized by
chaperone proteins -: Calreticulin, Erp57 , protein disulfide
isomerase(PDI) and tapasin .This complex is known as PLC (peptide
loading complex).

9.  Steps involve in endogenous pathway-:
Entering of pathogen inside the host’s cell. The pathogenic
protein degraded into smaller peptide (8- 16 peptide) by
cytosolic or nuclear proteosome.
Tapasin interacts with the transport protein TAP (transporter associated
with antigen presentation) which translocates peptide from cytoplasm into
the ER (endoplasmic reticulum).
Additional processing of protein done by ERAAP (ER
aminopeptidase associated with antigen processing).
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10. Peptide fragment bind to MHC I, then the chaperone
proteins are released and this peptide MHC-I complex
leave the ER and migrate to Golgi apparatus.
Peptide MHC-I complex move to the cell surface via golgi
apparatus through secreatory vesicles.
Peptide presented in complex with MHC-I can only be
recognized by CD-8+, T cells.
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11. ENDOGENOUS PATHWAY
TAP- Transporter
associated with antigen
presentation
ER- Endoplasmic
Reticulum
ERAD- ER associated
protein degradation
system
ERAAP- ER-
Aminopeptidase associated
with antigen processing

12.  Exogenous Pathway / Extracellular Pathway
OR
MHC Class II presentation
 In this pathway processing and presentation occours of
extracellular pathogen which replicate outside the host’s cell or
in body fluids.
 This pathway is mediated by MHC II molecules, that is
expressed by APCs like macrophages and dendritic cells , formed
in ER (endoplasmic reticulum) .
 Alpha and beta chain of MHC II molecule stabilizes By
Invarient chain.

13.  Steps involve in Exogenous Pathway
Internalization of pathogen through phagocytosis by APCs
and formation of endosome occours.
Lysosome of APCs fused with endosome and formation of
endolysosome takes place.
The proteolytic/ lysozymatic enzymes degraded the antigen
into peptide fragments ( 8-15 amino acids).
MHC class II two molecules transported from endoplasmic
reticulum to Golgi apparatus
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14. In Golgi apparatus due to acidic pH, proteases cathepsin S
and capthesin L are activated and digest invarient chain
and leave residual called CLIP (Class II associated invarient
chain peptide) in the peptide binding groove of MHC II.
5.
CLIP-MHC II COMPLEX released from from golgi apparatus through
secreatory vesicles. This vesicle fused with endolysosome and
release CLIP -MHC II complex. Here CLIP is replaced by pathogen’s
peptide fragment and formation of MHC II-peptide complex takes
place.
6.
Through exocytosis this MHC II-peptide complex reach to
cell surface (antigen presenting cell) and MHC II present
the peptide fragment of antigen to CD 4+ ,T-helper cells.
7.

15. MHC II ANTIGEN PRESENTATION PATHWAY Or EXOGENOUS PATHWAY
CLIP- Class II Associated
Invarient chain peptide

16. THANK YOU