Hyperacute rejection is due to –
**Core Concept**
Hyperacute rejection is a severe, immediate immune response against a transplanted organ, primarily mediated by pre-formed antibodies against the graft.
**Why the Correct Answer is Right**
The correct answer is due to the presence of pre-formed antibodies against the graft, which activate the complement system, leading to thrombosis, inflammation, and graft failure. This is often seen in ABO blood group incompatibility or in patients with previous sensitization to the graft. The antibodies bind to the endothelial cells of the graft, triggering a cascade of events, including the release of vasoactive substances, activation of platelets, and deposition of fibrin, resulting in microvascular thrombosis and graft dysfunction.
**Why Each Wrong Option is Incorrect**
* **Option A:** Hyperacute rejection is not typically associated with a cell-mediated immune response, which is more characteristic of acute rejection. Hyperacute rejection is primarily an antibody-mediated response.
* **Option B:** While acute rejection is a significant concern post-transplant, it is not the same as hyperacute rejection, which occurs immediately after transplant due to pre-formed antibodies.
* **Option C:** Chronic rejection is a late complication of transplantation, characterized by fibrosis and vascular disease, and is not associated with the immediate immune response seen in hyperacute rejection.
**Clinical Pearl / High-Yield Fact**
Hyperacute rejection is often preventable by cross-matching the donor organ with the recipient's serum to detect pre-formed antibodies against the graft. This emphasizes the importance of thorough pre-transplant evaluation and cross-matching in transplant medicine.
**Correct Answer: D. Pre-formed antibodies against the graft.**