Because a foreign graft or tissue is recognized
as being non-self by the immune system,
immunology has a very important role to
play in the science of transplantation.
So transplantation is the transfer of cells, tissue or an organ
between different parts of the body
or between different individuals.
Let’s look at some of the problems and
solutions that confront transplantation.
With a solid organ transplant, unless the transplant comes from
an identical twin, there will be immunological rejection.
With a bone marrow transplant or
other type of hematopoietic stem cell
transplantation, not only is there the
risk of the recipient rejecting the graft.
But because immunological cells are being given, there
is a risk of the graft reacting against the recipient.
In other words, graft-versus-host.
Tissue typing technology will allow
the matching of the donor and the
recipient with a reduced risk of rejection
and of graft-versus-host reactions.
Immunosuppressive drugs can dampen down the
recipient’s immune response against the foreign graft.
One of the major problems in
transplantation is availability.
There are many more people require
transplants than available organs.
So ways of developing increased
availability are very important.
One way which is being explored
is the use of a xenotransplant.
For example, a pig heart
into a human recipient.
Let’s have a look at the four different types
of way in which transplants can be classified.
An autograft is a graft from one part of the body
to another part of the body in the same individual.
For example, a skin graft or a saphenous
vein graft to replace a coronary artery.
An isograft is between genetically
identical, in other words monozygotic twins.
An allograft is the most common type of transplant, where
the graft is between different members of the same species.
A xenograft is between
members of different species.
As I’ve already mentioned, pig heart
valves for example, into human.
There are certain rules that govern whether
or not a transplant will be accepted.
These were initially developed
using inbred strains of mice.
We can see here two genetically
identical strain A mice.
You can transfer skin from one strain
A mouse to another strain A mouse.
And because they are genetically identical,
the skin graft will be accepted.
There will be no
However, if you take skin from a B strain mouse and transfer it
onto an A strain mouse, or from an A strain mouse and transfer
it onto a B strain mouse, then there will be foreign antigens
on the graft that will be recognized by the recipient mouse.
There will be an immunological reaction,
and the skin graft will be rejected.
Looking at the F1 hybrid of an A x B strain mouse, you
can see that A skin would be accepted on the F1 hybrid.
And B skin would also be
accepted on the F1 hybrid.
But if you took skin from the hybrid
mouse, the AB mouse, that would be
rejected if transferred either onto an
A strain mouse or a B strain mouse.
Because half the antigens in the F1
hybrid will be foreign to the recipient.
These kinds of experiments in inbred strains of mice led
the foundations of transplantation as we know it today.