TRANSPLANTATION:1

TRANSPLANTATION

• it is the act of transferring cells, tissues and organs from one site to another.
• joseph murray in boston performed transplantation for the first time of a kidney between identical twins.
•  Today, kidney, pancreas, liver, heart, lungs, bone marrow, and cornea are transplanted between nonidentical individuals too.
• the barrier making transplantation a routine treatment is the immune system.; because it treats the transplanted cells, tissues or organs as foreign .For this, a variety of immunosuppressive treatment is used but due to their effect on the whole immune system; their prolong or intensified use can be deleterious to the recipient.
• So, methods are being developed to induce tolerance to the graft without compromising with the immune responses overall.

Types of Transplants: Degree of immune response to a graft varies with the type of graft.
following are the type: 1) autograft, 2)isograf, 3)allograft, 4)xenograft.

Autograft-it is the transfer of cells or tissues from one place to another within an individual .e.g. transferring healthy skin from one site to another in the burnt patient, and use of healthy blood vessels to replace blocked coronary arteries.

Isograft-in this case, transplantation is carried out between genetically identical individuals. i.e. monozygotic twins in humans or syngeneic mouse.

Allograft-in this case, transplantation is carried out between genetically different members of the same species..e.g.  different strains of mouse, two different individuals in humans.

Xenograft-this is the transplantation between different species.. e.g. graft of a baboon heart into a human.
Due to shortage of organs, raising animals for donating organs is under serious consideration.

Graft rejection:

• Autograft and isograft show negligible or no intolerance at all to the graft.
• An allograft  being genetically dissimilar generate immune response and is rejected.
• Xenograft exhibit the greatest genetic difference and a vigorous graft rejection.

• The immune response leading to graft rejection shows the attributes of specificity and memory.

Experimental demonstration:

• suppose strain A is grafted with skin from strain B. then at first, it might take 12 to 14 days for rejection to occur ; because at first the graft becomes vascularized in few days ;followed by infiltration of graft by immune cells leading to immune response and then decreased vascularization and  visible necrosis.
•  But, rejection takes only 5-6 days to occur when strain A is again transplanted with skin from strain    B; this proves development of memory.
•  But these memory cells are specific in their action and this becomes evident when a totally different      strain C skin is grafted to strain A; strain C is genetically different from both A and B; and in this case,  again strain A mouse takes 12-14 days to reject the graft from strain C because strain A mouse had     not developed memory for strain C as it was their first encounter.