Mechanisms of allograft rejection

allograft rejection immunology

1. Mechanisms of Allograft Rejection By M.sri aravind lal B841018 M.sc genomics

2. Introduction Transplantation refer to the act of transferring cells, tissues or organs from one site to another . Disease can becured by implanation of a healthy organ, tisssues or cells (a graft) from one individual to another. The first successful human transplant which was between identical twins accomplished in boston in 1954.

3. Immunological basis of allograft rejection Allograft is tissue transferred between genetically different memberof the same species.In mice,an allograft is performed by transferring tissue or an organ from one strain to another. In humans,organ grafts from one individual to another are allografts unless the donor and recipient are identical twins.

4. Allograft rejection display specificity and memory The rate of allograft rejection varies according to the tissues involved.skin graft is faster than other tissue such as kidney or heart. If an inberd mouse of strain A is grafted with skin from strain B,primary graft rejection,known as first set rejection occurs. The vascularized transplant becomes infiltrated with lymphocytes,monocytes,neutrophils , other inflammatory cells.

5. CONT……… There is decreased vascularization of the transplanted tissue by 7-10 days, visible necrosis by 10 days and complete rejection by 12-14 days. Immunologic memory is demonstrated when a second strain Bgraft is transferred tona grafted strain A mouse. Complete rejection occur within 5-6 days – second set rejection

6. Graft rejection occurs in two stages Graft rejection is caused by a cell mediated immuno response to alloantigen expressed on cells of graft SENSITIZATION STAGE CD4+ and CD8+ T cells recognize alloantigen exprssed on cells of foreign graft and induces Tcell proliferation in the host. EFFECTOR STAGE Immune destruction of graft take place.

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8. Graft rejection reaction HYPERACUTE REJECTION REACTIONS Occurs within 24 hours of transpolantation Preexisting host serum antibody specific for antigen of graft. ACUTE REJECTION REACTIONS Mediated by Tcell responses and begin about in 10 days after tranplantation . CHRONIC REJECTION REACTION occurs from months to years after transplantation by both humoral and cell mediated responses by the recipient

9. Steps in hyperacute rejection