T cell recognizes which antigen in graft rejection
## **Core Concept**
The recognition of antigens by T cells is a crucial step in the immune response, including graft rejection. T cells recognize antigens presented by Major Histocompatibility Complex (MHC) molecules on the surface of antigen-presenting cells (APCs). In the context of graft rejection, the antigens recognized by T cells are primarily those expressed on the surface of the graft.
## **Why the Correct Answer is Right**
The correct answer, **B. MHC molecules**, is right because T cells recognize antigens that are processed and presented by MHC molecules on the surface of APCs. In graft rejection, the immune system recognizes the graft as foreign, largely due to differences in MHC molecules between the donor and the recipient. T cells, specifically T helper cells (CD4+) and cytotoxic T cells (CD8+), play a central role in this process by recognizing MHC class II and class I molecules, respectively, on the surface of the graft.
## **Why Each Wrong Option is Incorrect**
- **Option A:** This option is incorrect because while T cells can interact with various molecules on the surface of APCs, the primary recognition of antigens in the context of graft rejection is not through this mechanism.
- **Option C:** This option is incorrect because while co-stimulatory molecules are crucial for full T cell activation, they are not the primary antigens recognized by T cells in graft rejection.
- **Option D:** This option is incorrect because, although adhesion molecules play a role in the interaction between T cells and APCs or graft cells, they are not the primary antigens recognized in graft rejection.
## **Clinical Pearl / High-Yield Fact**
A key point to remember is that MHC molecules are polymorphic, meaning they have many different forms. This polymorphism is the main reason for graft rejection, as the recipient's T cells recognize the donor's MHC molecules as foreign. Matching MHC types between donor and recipient is crucial in organ transplantation to reduce the risk of rejection.
## **Correct Answer:** B. MHC molecules