50 ĐỀ LUYỆN THI IOE LỚP 9 - NĂM HỌC 2022-2023 (CÓ LINK HÌNH, FILE AUDIO VÀ ĐÁ...
MAJOR HISTOCOMPATIBILITY COMPLEX
1. PRESENTED BY: PRADDUM KUMAR NAMDEV
BSc (Hons) ZOOLOGY 6th sem.
MAJOR HISTOCOMPATIBILITY
COMPLEX
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2. THIS PRESENTATION INCLUDES:
What are MHCs?
What do MHC do
Types of MHC
MHC class І
MHC class ІІ
MHC class ІІІ
MHC molecules and antigen presentation
Features of MHC class I and II
Peptides of MHC class I and II
Important aspects of MHC
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3. WHAT ARE MHCS?
Discovered by Peter Gorer in 1930
Major histocompatibility complex (MHC) is tightly linked
cluster genes present in every vertebrate species, the
product of which play in intercellular recognition and in
discrimination between self and nonself.
MHC is located on chromosome 6 in humans and
chromosome 17 in mice (HLA – Human leukocyte
antigen) complex and H-2 (histocompatibility- 2)
respectively.
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4. CONTD…
MHC genes are organized 3 classes
A. Class І MHC genes
Glycoproteins expressed on all nucleated cells
Major function to present peptide Ags to Tc cells
B. Class ІІ MHC
Glycoproteins expressed on Mф, B cells, DCs
Major function to present processed Ags peptide to TH cells
C. Class ІІІ MHC
Class III molecules are not membrane proteins, are not related
structurally to class I and class II molecules, and have no role in
Ag presentation, although most play some role in immune
response. e.g. C2, C4a, C4b, factor B21-hydroxylase enzymes,
TNFα, TNFβ, heat shock proteins (HSP).
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5. WHAT DO MHCS DO?
MHCs bind to peptide fragments (parts of chopped
up through phagocytosis by APCs) and
display/present them on the surface of the cell.
The T cells monitor the MHCs for evidence of an
invasion of a cell or for foreign cell.
B cells do not interact with MHCs directly but come
into action after stimulation by T cells.
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6. TYPES OF MHCS…
CLASS І MHC molecules
Molecular weight 45KD
Found on almost all nucleated cells (except RBCs)
Bonds to portions of antigens (peptide fragments )
Presents them on the cell surface.
Cytotoxic T cells can recognize and begin specific
defense.
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7. CONTD…
It is membrane spanning molecule approx. 350 amino
acids in length, 75 amino acids comprising the
transmembrane and cytoplasmic portions. The
remaining 270 amino acids are divided into three
globular domains α-1, α-2 and α-3
The alpha chain is trans membrane glycoprotien
encoded by A,B and C regions of human HLA
complex and within the K and D regions of mouse H-2
complex
The second portion of the molecule is globular protein
called β-2 microglobulin associactes with the α-3
domain and is necessary for MHC stability.
Microglobulin is a protein encoded by highly
conserved gene located on different chromosomes.
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8. CONTD…
the β2 microglobulin is non covalently associated with the
α3 domain.
The α1 and α2 domains interact to form 8 antiparallel β
strands spanned by 2 long α helical regions. The region is
capable of binding (via non-covalent interactions) as small
peptide of 10 amino acids. This small peptide is
“presented” to a T-cell and defines the antigen “epitope”
that the T-cell recognizes.
The peptide-binding cleft is located on the top surface of
the MHC class І molecule and it is enough to bind a
peptide 8 to 10 amino acids. 8
9. STRUCTURE OF MHC І
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Fig.1 MHC I molecules are composed of a polymorphic
chain non covalently attached t a non polymorphic
microglobulin (β2m). The α-chain is glycosylated
10. CONTD…
Between the α-1 and β-2 domains lies a region very
similar to that seen in the class І molecule. This region,
bounded by a β- pleated sheet on the bottom and two
alpha- helices on the sides, is capable of binding (via
non-covalent interactions) a small peptide of about 10
amino acids, this small peptide is presented to a T-cell
and defines the antigen “epitope” that the T-cell
recognise.
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11. CLASS ІІ MHC MOLECULE
Class ІІ molecules are composed of two polypeptide
chains.
These polypeptides (alpha and beta) are about 230 and
240 amino acids long respectively, and are glycosylated,
giving molecular weights of about 33 kDa 28 kDa.
The polypeptides fold into two separate domains; α1 and
α2 for the alpha polypeptide, and β-1 and β-2 for the beta
polypeptide.
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12. STRUCTURE OF MHC ІІ MOLECULE
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Fig.2 MHC II molecules are composed of a polymorphic α-chain
non-covalently attached to a polymorphic β-chain. Both are
glycosylated
14. MHC CLASS ІІІ MOLECULE
These are heterogeneous molecules
Include complement component C2, C4 and factor
B (components responsible for formation of C3
convertase)
They also include heat shock proteins and tumour
necrosis factor.
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15. MHC MOLECULES AND ANTIGEN
PRESENTATION
Both type of membrane glycoproteins (class I and class II
MHC) function as highly specialised antigen-presenting
molecules.
The class I and class II MHC molecule present antigen to T-
cells.
Antigen recognition is mediated by αβ or γδ T-cell antigen
receptors (TCR).
T-cell recognize only combined with MHC molecules.
Class I molecule present processed endogenous Ag to CD8 T-
cells.
Class II molecule present processed exogenous Ag to CD4 T-
cells.
Exogenous antigens are those antigens that originate outside
the organism or cell whereas endogenous antigens originates
within the organism or cell. 15
18. PEPTIDES OF MHC I & MHC II
Class I MHC molecule present a peptide of 8-10
amino acids and are endogenous.
Peptide bind MHC due to presence of specific a/a
found at the ends of peptide.
e.g. Gycine @ position 2.
Class II MHC molecules bind and present slightly
longer peptides of 13-18 amino acids, processed
through endocytic pathway.
Non peptide antigens (such as glycolipid,
phospholipid) are presented by members of the
CD1 family related to non classical class MHC I.
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19. IMPORTANT ASPECTS OF MHC
MHC molecules (class I and class II) are membrane
bound; recognition by T- cells requires cell-cell contact.
Because each MHC molecule can bind to many different
peptide, binding id termed degenerate.
Although there is high degree of polymorphism for a
species, an individual has maximum 6 different class I
MHC products and only slightly more class II MHC
products (considering only the major loci).
Each MHC molecule has only one binding site.
The different peptides can bind to a given MHC molecule
to the same site, but only at a time.
MHC polymorphism determined only in the germline.
There are no recombination mechanism for generating
diversity, 19
20. CONTD…
Alleles for MHC genes are codominant.
Each MHC gene product is expressed on the cell
surface of an individual nucleated cells.
Cytokines (especially interferon-γ) increase level of
expression of MHC.
Endogenous peptide associate with class I MHC are
recognised by TC cells.
Exogenous peptide associate with class II MHC are
recognised by TH cells.
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21.
LIFE SCIENCES
FUNDAMENTALS AND PRACTICES -1
(PATH FINDER PUBLICATION)
BY- PRANAV KUMAR
www.slideshare.com
www.immunologynotes.com
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References