Download 203.transplantation

Major Histocompatibility Complex
and Transplantation
• Major histocompatibility complex (MHC) proteins were
discovered for the first time with the beginning of tissue
transplantation
• The success of tissue and organ transplantation depends
upon the donor’s and recipient’s “human leukocyte
antigens” (HLA) encoded by HLA genes
• These proteins ( MHC ) are allo-antigens which means :
the same gene locus ( site ) in different individuals of the
same species will express different antigens ( proteins ) ,
so when one antigen of one individual is transported to
another who doesn’t have it , it will induce immune
response against it ] like blood groups [
Major Histocompatibility Complex
and Transplantation
• Genes for HLA proteins are
clustered in the MHC complex
region located on the short arm
of chromosome 6
• Three genes HLA-A, HLA-B and
HLA-C code for Class I MHC
proteins
• HLA-D loci encode for Class II
MHC proteins ie, DP, DQ and
DR
Major Histocompatibility Complex
and Transplantation
• Each individual has two “haplotypes” ie, ( two sets of
these genes one paternal and one maternal )
• These genes are very diverse “polymorphic”
– There is about 47 HLA-A genes
– There is about 88 HLA-B genes
- There is about 29 HLA-C genes
– There is about More than 300 HLA-D genes
So the child will have a different combination of genes different
from his parents and from any other person ( except for
identical twins )
Major Histocompatibility Complex
and Transplantation
•
•
•
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Minor HLA genes – are unknown
They mount a weak immune response
Play role in chronic rejection of a graft
There are no laboratory tests to detect minor
antigens
• Class III MHC locus found between MHC I & II
regions
• Encode for TNF, lymphotoxin, complement
proteins ( C2 and C4 )
MHC Class I, II & III Genes
MHC Class I Proteins
• They are glycoproteins found on surface of virtually all the
nucleated cells
• The A locus which have HLA-A genes encode 20 different
proteins , B locus having HLA-B genes will encode 40
different proteins and C locus will encode 8 different
proteins
• So the different proteins will make the individuals differ from
each other
• all class I proteins are composed of a heavy chain (α1 + α2 +
α3 ) bound to a 2-microglobulin molecule
• The heavy chain is highly polymorphic and has a
hypervariable region at N-terminal
– Polymorphism – self and non-self recognition
– Constant regions react with CD8 protein of
Tcytotoxic
MHC Class I Protein
The polymorphism happen
in the α chain ( heavy
chain )
And the α chain (
specially α3 domain ) has
transmembrane part which
contact with the
intracellular part of α chain
Class II MHC Proteins
• They are glycoproteins normally found on the surface
of antigen presenting cells such as ( marophages, B
cells, dendritic cells of spleen and Langerhans cells of
skin
• They are highly polymorphic
• Composed of two polypeptide chains bound noncovalently
• They have hypervariable regions leading to
Polymorphism
MHC Class II Protein
Here the polymorphism
found in both α and β
chains
And both α and β chains
have a transmembrane part
to contact it’s intracellular
part
Major Histocompatibility Complex
and Transplantation
• Both chains of Class II MHC proteins are
encoded by the MHC locus
• Constant regions of both the peptides
interact with CD4 proteins of helper T cells
Biologic Importance of MHC
• Tc kills virus infected cells in association
with class I MHC proteins
• Helper T cell recognize antigen in
association with class II MHC proteins
• This is called MHC restriction
• Success of organ transplant is determined
by compatibility of the MHC genes between
the donor and the recipient
Transplantation antigens
Compatible ,
so there is no
immune
response
against the
graft
Non –
compatible
, so there is
immune
response
against the
graft
Transplantation
Transplantation
• Types of transplants:
– Autografts or ( Autologous grafts )
• Donor and recipient are the same person
• Common in skin grafting; bone marrow
– Syngeneic grafts or ( isograft )
• Donor and recipient are genetically
identical
• Animal models; identical twins
Transplantation
• Types of transplants:
– Allogeneic grafts ( allograft ) very imp
• Donor and recipient are in the same species,
but genetically unrelated
• Common : heart, lung, kidney, liver graft
– Xenogeneic grafts ( xenograft )
• Donor and recipient are different species
• Like graft from Animal to humans
– Artificial grafts
Like artificial joints and skin
Transplantation
• Major Barrier to transplantation is the immune
response
– T cells play primary ( main ) role in graft rejection
– B cells can/do play a role
– Classic adaptive/acquired immune response
• Memory
• Specificity
1st set versus 2nd set reactions
Transplantation
In the previous picture :1- in column ( a ) there is in autograft of epidermis from the same
person , so there will be no immune response against it and no
rejection
2- in column ( b ) there is allograft from human to another human ,
there will be a rejection if they don’t match , but it will take long time
( up to 14 days ) because he exposed to it for the first time ( hens
called first- set rejection )
3 – in column ( c ) we repeat the step 2 but the rejection happen faster
because there is memory cell which directly get activated ( called
second-set rejection ) it is always faster ( up to 6 days )
1st set versus 2nd set reactions
Role of cell mediated responses
Unprimed syngeneic
recipient
Transplantation
In the previous slide
There is 2 syngeneic mice ( like identical twins ) , the first one get skin
graft that doesn,t match , so after 14 days the grafted skin get rejected
by the first-set rejection
Now the T cells have memory cells , if we transplant another skin graft
to the same mouse the rejection will happen in 6 days due to the
memory cells
If we transport the T memory cells to the other mouse who didn’t have
skin graft , and then give him a skin graft it will reject it in 6 days due
to the presence of T memory cells
And that tells that T cells have a main role in graft rejection
Role of CD4+ versus CD8 T+ cells
Injecting recip. mice with mab to
deplete one or both types of T cell
Transplantation
] In the previous slide [
This slid will tell you which type of T cell is dominant or have the
main function in graft rejection :
1- when we transplant a graft that doesn’t match and give the recipient
an ( anti CD8 ) the graft will stay intact for about 15 days before it get
rejected
2 – when we transplant a graft that doesn’t match and give the
recipient an ( anti CD4 ) the graft will stay intact for about 30 days
before it get rejected
That tells you that the CD4 cell have the main function in graft
rejection
And if we block both CD4 and CD8 the grafr will persist for 60 days
Transplantation
• T cells play primary role in 1st and 2nd set
rejection reactions
– Nude mice ( don’t have T cells ) accept allografts
– B cell deficient mice reject allografts , because they still
have T cells
A Nude
mouse has
a transplant
of rabbit
skin
Mechanisms involved in Graft Rejection
Sensitization stage = = = = Effector stage
Rejection Response
Clinical manifestations of graft rejection
I.
Hyperacute rejection: very quick ( within minutes )
II.
Acute rejection: about 10 days (cell mediated)
III. Chronic rejection: months-years (both) by minor HLA gene
Clinical manifestations of graft rejection
Hyperacute rejection ( mediated by humoral immunity ) :
In this condition , the recipient already have antibodies against the graft
even before the transplant , so when we transplant the organ the preexisting antibodies will attach to the organ and activate the complement
system to destroy the organ within minutes
Acute rejection ( cell mediated ) :
In this condition , the graft persist for about 10 days ( in contrast to
hyperacute which is in minutes ) and that due to the action of T cells
this reaction is cell mediated so take longer time to multiply and arrive
to the site of graft
Chronic Rejection
( cell mediated and humoral immunity )
– This occurs months to years after engraftment
– Main pathologic finding in chronic rejection is
atherosclerosis of the vascular endothelium
– Main cause of chronic rejection is not known
• Minor histocompatibility antigen miss match
• Side effects of immunosuppressive drugs
Graft-versus-Host (GVH) Reaction
• Some times the patient need a transplanted bone marrow or
thymus which are have a large number of lymphocytes from
the donor
• So when the graft is allograft ( from the same species but not
identical ) the transplanted lymphocyte ( specially T cells ) will
lock around in the recipient body if it didn,t find a match in the
MHC it will attack the recipient body because it look foreign
bodies for it
• so in this case instead of making the patient healthier , he will
become worse
Graft-versus-Host (GVH) Reaction
The donor’s cytotoxic T cell will play a
major role in destroying the recipient’s
cells
Symptoms are: maculopapular rash,
jaundice, hepatosplenomegaly and
diarrhea
GVH reactions usually end in infections
and death
So in brief the transplanted organ will
work against or versus the host
Maculopapular rash
HLA Typing in the Laboratory
• Prior to transplantation , laboratory test commonly
called as HLA typing or tissue typing is performed
to determine the closest MHC match between the
donor and recipient is performed
• Methods applied in this test is :
–
–
–
–
DNA sequencing by Polymerase Chain Reaction (PCR)
Serologic Assays
Mixed Lymphocyte Reaction (MLR)
Crossmatching – (D) lys + (R) serum + complement ( very
important )
Tissue Matching
Effect of HLA class I & II matching on survival of kidney grafts
Zero = means no difference
So the MHC match
Notice that class II is more
important than class I
So when it is zero or close
to zero the survival rate
increase
Tissue Matching
Serological Method
In this test you take the recipient’s
serum which contain antibodies
and then add to it the donor’s
HLA antigens
Then add complement to them , if
the antibodies bind to the HLA
antigens the complement will be
activated and will attack the
donor’s cells and then add a dye
to confirm the lysis
If the dye radiate ( visible ) that
mean the recipient will reject the
graft , if not he will except it
Tissue Matching
Mixed Leukocyte Reaction (MLR)
In this test we will take leukocytes from the recipient and the donor and but them in
tube , if the MHC in the different leukocytes don’t match they will be activated
against each other and proliferate , then we add a radioactive material ( thymidine )
which will be incorporated into the DNA and it will radiate ( become visible ) , if the
MHC match ther will be no proliferation and the thymidine will not be taken by the
cell’s DNA
Tissue Matching
Very important
General Immunosuppression Therapy
After the transplantation
1) Mitotic inhibitor : azathioprine ( pre & post )
2) Corticosteroids: (+ 1)
3) Cyclosporin A, FK506: IL-2 and IL-2R
4) Total lymphoid irradiation
Immunosuppresive Therapy
Immunosuppresive Therapy
Cyclosporin
FK506
Immunosuppresive Therapy
Here you see the
survival of the graft
with and without the
immunosuppresive
therapy
The blue = with
The black = without
Specific Immunosuppression
Therapy
a) Mabs (Monoclonal antibody ) to T cell components or
cytokines
b) Agents that blocking co-stimulatory signal
Immunosuppresive
Therapy
• Downsides
– Must be maintained for life
– Toxicity
– Susceptibility to infections
– Susceptibility to tumors ( due to inactivation of CD8 )