Question

Why are the transplanted tissues rejected and what are the means to prevent rejection?

Answer 1

The transplanted organ contains about 40 antigens (HLA proteins) which act as self-markers. The recipient's body recognises these as foreign (non-self) antigens and produces antibodies and T-cells against them, which destroy the transplanted organ. This is called rejection.

Means to prevent rejection

(i) Use of immunosuppressants: Drugs such as cyclosporin A counteract the immune system and stop the production of antibodies against the transplanted organ. They are expensive and also make the patient prone to infections, so they must be taken throughout life. 

(ii) Transplant from a sibling: If the organ is taken from a brother, sister or identical twin, the chances of acceptance are greater as they have a similar genetic constitution (matched HLA). 

(iii) Use of X-irradiation on bone marrow and lymph tissues: This suppresses blood cell production and slows the phenomenon of rejection. 

(iv) Tissue typing: Proper matching of the HLA antigens of donor and recipient before transplantation. The preference order is identical twin > sibling > parent > unrelated donor.

Transplantation is successful only when HLA matching is good and immunosuppressants are used to prevent rejection of the graft.