Graft rejection is classified into hyperacute, acute, and chronic, on the basis of time taken for the rejection, types of immune response mounted against the graft and clinical and pathologic features (Table 1).

Table1. Comparison of various types of graft rejection.

hyperacute Rejection

This occurs within minutes to hours of transplantation and is characterized by thrombosis of graft vessels and ischemic necrosis of the graft.

- It is mediated by circulating antibodies that are specific for antigens on the graft endothelial cells and that are present before transplantation

- In an individual, exposure to foreign HLA antigens can occur as a consequence of previous blood transfusions, pregnancy, or organ transplantation. Following which, the individual develops antibodies against these antigens. These preformed antibodies may be anti-ABO or anti HLA specific for allogenic (i.e. graft’s) MHC molecules. If an individual with these pre-existing antibodies to a foreign HLA antigen receives a graft (containing same foreign HLA antigen), then the graft will be rejected earlier and more vigorously (Fig. 1)

- Hyperacute rejection is not a common problem in clinical transplantation, because it can be avoided by matching the donor and the recipient. Potential recipients are tested for antibodies against the prospective donor’s blood group antigens (by cross matching) and HLA antigens (by HLA typing).

Fig1. Hyperacute graft rejection.

Acute Graft Rejection

 Acute graft rejection occurs within days or weeks after transplantation. It is due to an active immune response of the host stimulated by alloantigens in the graft.

- Acute graft rejection is mediated by T cells (mainly cytotoxic T cells, occasionally helper T cells) and antibodies specific for alloantigens in the graft

- Cytotoxic T cells directly destroy the graft cells, or cytokines secreted by the helper T cells induce inflammation, which destroys the graft

- Antibodies contribute especially to the vascular component of acute rejection. Antibody-mediated injury to graft vessels is caused mainly by complement activation by the classical pathway (Fig.2)

- Current immunosuppressive therapy is designed mainly to prevent and reduce acute rejection by blocking the activation of alloreactive T cells.

Fig2. Acute graft rejection.

Chronic Graft Rejection

Chronic graft rejection is an indolent form of graft damage that occurs over months or years, leading to progressive loss of graft function.

- Chronic rejection may be manifested as fibrosis of the graft and by gradual narrowing of graft blood vessels, called graft arteriosclerosis

- T cells that react against graft alloantigens secrete cytokines, which stimulate the proliferation and activities of fibroblasts and vascular smooth muscle cells in the graft. The smooth cell proliferation in the vascular intima may represent a specialized form of chronic delayed type hypersensitivity (DTH) reaction (Fig. 3)

- Alloantibodies also contribute to chronic rejection Chronic rejection is refractory to most of the therapeutic options available and is becoming the leading cause of graft failure.

Fig3. Chronic graft rejection.

اخر الاخبار

اخبار العتبة العباسية المقدسة

وزارة التعليم العالي تكرم جامعة العميد لحصولها على جائزة المكتبة الأكاديمية المتميزة

جمعية العميد تناقش استعداداتها لانطلاق فعاليات المؤتمر العلمي الرابع لإحياء تراث أمير المؤمنين (عليه السلام)

أكاديمية التطوير الإداري تواصل برنامج الخطة الخمسينية لعدد من ملاكات العتبة العباسية المقدسة

المجمع العلمي يواصل تقديم دورته التطويرية لعدد من الملاكات التربوية في الديوانية

المزيد

الآخبار الصحية

الرياضة وحدها لا تكفي.. كيف يؤثر الجلوس الطويل على الصحة؟

دراسة: بدائل السكر ليست آمنة على الكبد

تفاحة قبل النوم.. عادة بسيطة مفيدة أم خطر على الصحة؟

احذر مشاركتها مع الآخرين.. 3 أدوات شائعة قد تنقل أمراض خطيرة

المزيد

الآخبار التكنلوجية

الهنغاري لاسلو كراسناهوركاي يفوز بجائزة نوبل للآداب 2025

رسميا.. إعلان الفائز بجائزة نوبل للسلام لعام 2025

باحثون: تشات جي بي تي ونماذج الذكاء الاصطناعي يمكن "تسميمها"

عالمان في الأعصاب يرفعان دعوى قضائية ضد شركة آبل

المزيد

مواضيع ذات صلة

Cancer Immunotherapy

Tumor Antigens

Mechanism Of Graft Rejection

Factors Influencing Allograft 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