Preformed antibodies cause
**Core Concept**
The question is testing the understanding of **preformed antibodies** and their role in transplantation and blood transfusion reactions. **Preformed antibodies** are immunoglobulins that are already present in the body, often as a result of previous exposure to **antigens**.
**Why the Correct Answer is Right**
Preformed antibodies can cause **hyperacute rejection** in organ transplantation and **hemolytic transfusion reactions**. This occurs when the antibodies react with **antigens** on the surface of the transplanted organ or transfused blood cells, leading to rapid activation of the **complement system** and **coagulation cascade**.
**Why Each Wrong Option is Incorrect**
**Option A:** Incorrect because it is not directly related to the effects of preformed antibodies.
**Option B:** Incorrect as it does not accurately describe the consequence of preformed antibodies.
**Option C:** Incorrect because, although related to immune responses, it is not the direct consequence of preformed antibodies.
**Clinical Pearl / High-Yield Fact**
Preformed antibodies are a critical consideration in **ABO blood group compatibility** and **human leukocyte antigen (HLA) matching** for organ transplantation to prevent adverse reactions.
**Correct Answer:** D. Hyperacute rejection