## **Core Concept**
The question pertains to the type of immunological reaction involved in endothelial corneal graft rejection. This involves understanding the immune response to transplanted tissues, specifically the cornea, and the mechanisms of graft rejection.

## **Why the Correct Answer is Right**
The correct answer, **cell-mediated immunity (Type IV hypersensitivity reaction)**, is right because endothelial corneal graft rejection primarily involves T lymphocytes. These T cells recognize the graft as foreign and orchestrate an immune response against it. This process includes the activation of various immune cells and the release of cytokines, leading to inflammation and damage to the graft. The endothelium of the cornea is particularly sensitive to immune-mediated damage, which can lead to graft edema and failure.

## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because **immediate hypersensitivity (Type I)** reactions involve IgE antibodies and the release of histamine, leading to allergic responses. This is not the primary mechanism in corneal graft rejection.
- **Option B:** This option is incorrect because **antibody-dependent cytotoxic hypersensitivity (Type II)** involves antibodies directed against antigens on the surface of cells, leading to cell destruction. While antibodies can play a role in graft rejection, the primary mechanism in endothelial corneal graft rejection is not Type II hypersensitivity.
- **Option C:** This option is incorrect because **immune complex-mediated hypersensitivity (Type III)** involves the deposition of antigen-antibody complexes, leading to complement activation and inflammation. This mechanism is also not the primary pathway in endothelial corneal graft rejection.

## **Clinical Pearl / High-Yield Fact**
A key point to remember is that corneal graft rejection can present with signs such as corneal edema, inflammation (iritis), and endothelial rejection line. Early recognition and treatment with corticosteroids can often reverse the rejection process. Understanding the immunological basis of graft rejection is crucial for managing transplant patients.

## **Correct Answer:** . **cell-mediated immunity**