The rate of allograft rejection varies according to the

- Tissue involved, e.g. skin grafts are rejected faster than other tissues such as kidney or heart

- Genetic distance between the donor and recipient— More the genetic distance; faster is the rejection. Autografts and isografts are well accepted

- Immunological memory: Rejection is faster when another graft is placed to a recipient from the same donor. This occurs due to the memory cells produced against the first graft would differentiate quickly into effector cells; and that in turn reject the second graft faster.

An example is given below which describes the pathological sequences that take place when a skin graft is placed: (1) as an autograft to the same donor (leads to acceptance), (2) as an allograft to a recipient for the first time (leads to first set rejection), (3) as an allograft to the same recipient for the second time (leads to second set rejection).

Autograft Acceptance

When a skin graft is transplanted to the same individual at a different site, revascularization takes place by day 3–7; followed by healing (within day 7–10) and then resolution and acceptance of the graft (by day 12–14) (Fig. 1A)

Fig1. A to C: Graft acceptance and graft rejection.

first-set Rejection

 When an allograft is placed for the first time from a donor to a recipient, the type of primary graft rejection that develops is known as, first-set rejection (Fig. 1B).

- The skin first becomes revascularized between days 3 and 7; as the reaction develops, the vascularized transplant becomes infiltrated with lymphocytes, monocytes, neutrophils, and other inflammatory cells

- There is decreased vascularization of the transplanted tissue by 7–10 days, visible necrosis by 10 days, and complete rejection by 12–14 days.

Second-set Rejection

If, in a recipient who has rejected a graft by the first set response, another graft from the same donor is transplanted, it will be rejected in an accelerated fashion.

- Though vascularization starts but is soon interrupted by the inflammatory response

- Necrosis sets in early and the graft sloughs off by the sixth day (Fig. 1C).

اخر الاخبار

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مواضيع ذات صلة

Cancer Immunotherapy

Tumor Antigens

Mechanism Of Graft Rejection

Types of Graft Rejection

Histocompatibility Antigens

Disorders of Phagocytosis

Combined Immunodeficiencies (B and T Cells Defects)

Cellular Immunodeficiency (T Cell Defects)

Neuropathies

Humoral Immunodeficiency (B Cell Defects)

Type IV Hypersensitivity Reaction

Type III Hypersensitivity Reaction