The document discusses antigen processing and presentation pathways. It explains that antigen presenting cells digest proteins from inside or outside the cell and display the resulting peptide fragments on MHC class I or II molecules. MHC class I presents endogenous antigens processed via the cytosolic pathway, while MHC class II presents exogenous antigens processed via the endocytic pathway for recognition by T cells. This process allows the immune system to detect signs of infection or abnormal growth.

1. Submitted To –
Dept.of Biotechnology
Presented By –
Sonika Chouhan
M.Sc. II Sem

2.  Introduction
 Major Histocompatibility factor (MHC)
 Class I MHC molecule
 Class II MHC molecule
 Endogenous antigen
 Exogenous antigen
 Role of antigen presenting cells (APCs)
 Processing and presentation pathway
 The cytosolic pathway for endogenous antigen
 The endocytic pathway for exogenous pathway

3.  The process by which antigen presenting cells digest proteins
from inside or outside the cell.
 It display the resulting antigenic peptide fragments on the cell
surface MHC molecules for recognition by T cells is central to
the body’s ability to detect signs of infection or abnormal
growth.
 Antigen recognition by the T cells and B cells require
appropriate and processed antigens displayed on the cleft of
different MHC molecules.

4.  The B cells & T cells recognizes antigen process by different
pathways.
 The B cell recognizes the soluble form antigens like – protein ,
nucleic acid , some lipids and small amount chemical .
 T cells recognizes mainly protein as antigen.
 T cells recognizes whether Ag is in cytosol or in vesicular
system .
 T cells require the Ag should degraded in small peptides
(process called Ag processing).
 Then associated with MHC molecule intracellular then
peptide- MHC complex is displayed on cell surface ( process
called Ag presentation).

5.  Ag processing splits the protein into small fragments
or subunits about 8-10 aa and present them to T cells
.
 The cell presenting the Ag peptide acts as single
information about the origin of cell and pathway by
which the Ag processed and on MHC class I or II
molecule.

6. The MHC is a set of all cell surface proteins essential for
acquired immune system to recognize foreign molecules
in vertebrate which in turn determine histocompatibility.
Function-
MHC molecule Peptide
fragments
Cell surface (Display)
Recognize by T
cell

7.  It contain a large alpha
associated with beta2
microglobulin molecule
form heterodimer
 Alpha chain consists of
three extracellular domain
(a1,a2,a3)
 The class I MHC molecule
higher conc. Found on B
cells , T cell
&macrophages
 It consists of two
polypeptide chain alpha &
beta.
 Each contain external
domain (a1,a2)(b1,b2).
 The distal domain of both
form the Ag binding cleft
for processed Ag.
Class I MHC Molecule Class II MHC Molecule

8.  K.Ziegler and E.R Uranuae obseved that the Ag processing
is necessary for TH cell activation.

9.  Almost all nucleated cells express class I MHC
molecule and
 Displayed the processed Ag to CD8+ Tc cells
 These are also referred as target cells.
 Class II MHC molecule display processed Ag to CD4+
TH cells .
 These are referred as antigen presenting cells (APCs).

10.  If Ag present in cytosol i.e. endogenous Ag
 Ag is processed and presented on Class I MHC by a
pathway known as cytosolic pathway .
 The peptide - Class I MHC present on the target cell
interact with TCR and CD8 receptor of Tc cells.
 If Ag present in vesicular i.e. exogenous Ag
 It is processed and presented on Class II MHC by
endocytic pathway.

14.  Pathogen and Ag need to be partially degraded into
peptides before they before they bind MHC
molecules and are presented on the surface of an
APC.
 Newly synthesized MHC molecule either the
endocytic (MHC class II) , cytosolic (MHC class I) and
bind the Ag derived protein to the cell surface.

15.  Kuby Immunology
 Life – The science of biology.