Graft rejection || Immunological basis of graft rejection

Summary

This video explores the immunological basis of graft rejection, a critical process in tissue transplantation. It explains different types of grafts (autografts, isografts, allografts, and xenografts) and the risks of rejection, particularly with allografts. The video covers the immune mechanisms behind graft rejection, highlighting the roles of T cells, dendritic cells, and macrophages. It also discusses the timeline of rejection, with first and second-set rejections occurring at different speeds. Lastly, it emphasizes the importance of HLA typing in reducing rejection risks, offering a comprehensive understanding of graft rejection in medical procedures.

Takeaways

• 😀 Graft rejection occurs when the immune system recognizes a transplanted tissue as foreign and mounts an immune response against it.
• 😀 Tissue grafting is a critical process for medical treatments like skin grafts for burn victims, but graft rejection poses a significant risk.
• 😀 There are four types of grafts: autografts (from the same individual), isografts (from genetically identical individuals), allografts (from genetically different individuals of the same species), and xenografts (from different species).
• 😀 The most common graft rejection occurs with allografts, where the immune system attacks the foreign tissue unless specific matching criteria are met.
• 😀 In the case of autografts, tissue is typically accepted without rejection, as it comes from the same individual and is not recognized as foreign.
• 😀 Graft rejection can occur in two phases: the sensitization phase (where the immune system recognizes the graft as foreign) and the effector phase (where immune cells damage or destroy the graft).
• 😀 The sensitization phase involves immune cells like dendritic cells and macrophages presenting antigens from the graft to T-helper cells, triggering an immune response.
• 😀 T-helper cells, once activated, secrete cytokines like IL-2 and IL-6, which further activate other immune cells, including cytotoxic T cells, macrophages, and B cells, leading to graft rejection.
• 😀 Cytotoxic T cells (CD8+) directly destroy graft tissue by releasing perforin and granzyme, which induce apoptosis in the graft cells.
• 😀 HLA typing is crucial before transplantation to match the donor and recipient's immune systems, reducing the chances of graft rejection and improving the success of the transplant.

Q & A

What is graft rejection?

Graft rejection occurs when the recipient's immune system identifies the graft as a foreign object and attacks it. It is a common phenomenon in surgical procedures involving tissue grafting, such as skin grafts for burn treatment.

What are the different types of grafts mentioned in the video?

The video discusses four types of grafts: autograft (tissue taken from the same individual's body), isograft (graft between genetically identical individuals), allograft (graft between members of the same species but with different genetics), and xenograft (graft between different species).

Why is graft rejection more likely in allografts?

Graft rejection is more likely in allografts because the genetic makeup of the donor and recipient may differ, triggering an immune response in the recipient's body. The immune system may recognize the graft as foreign and attempt to reject it.

What happens during the revascularization phase after a graft is performed?

In the revascularization phase, blood vessels begin to form underneath the grafted tissue, allowing it to start receiving blood supply. However, immune cells may also infiltrate the grafted area, leading to potential rejection if the graft is recognized as foreign.

What is the difference between first-set and second-set graft rejection?

First-set graft rejection occurs within 14 to 15 days after the graft is placed, while second-set rejection happens much faster, typically within 10 days, when a second graft is transplanted into the same recipient after an initial rejection.

How do T cells contribute to graft rejection?

T cells, particularly T helper cells (CD4) and cytotoxic T cells (CD8), play a critical role in graft rejection. They are activated by foreign antigens on the graft and launch an immune response, which leads to tissue damage and rejection of the graft.

What is the role of dendritic cells in the graft rejection process?

Dendritic cells present antigens from the graft to T cells, signaling the immune system that the graft is foreign. This initiates the immune response that can ultimately lead to graft rejection.

What are some of the cytokines released during the graft rejection process?

Cytokines such as IL-2, IL-6, and interferon-gamma are released during graft rejection. These cytokines activate other immune cells, such as cytotoxic T cells and macrophages, leading to inflammation and tissue damage in the graft.

How can graft rejection be prevented?

Graft rejection can be minimized by performing HLA typing to match the donor and recipient as closely as possible. By matching the Human Leukocyte Antigen (HLA) molecules, the immune system is less likely to recognize the graft as foreign and reject it.

Why are T helper cells and cytotoxic T cells both important in graft rejection?

T helper cells (CD4) and cytotoxic T cells (CD8) are both essential in graft rejection. T helper cells activate other immune cells, while cytotoxic T cells directly attack the graft. Blocking both types of T cells can prolong graft survival.