Cell surface molecules involved in peripheral tolerance
**Core Concept**
Peripheral tolerance is a mechanism by which the immune system prevents autoimmune diseases by avoiding responses to self-antigens. Cell surface molecules play a crucial role in inducing and maintaining peripheral tolerance by interacting with T cells and other immune cells.
**Why the Correct Answer is Right**
The correct answer involves molecules that are expressed on the surface of antigen-presenting cells (APCs) and interact with T cells to induce tolerance. These molecules include PD-L1 (programmed death-ligand 1) and CTLA-4 (cytotoxic T-lymphocyte-associated protein 4) ligands. PD-L1 interacts with PD-1 on T cells, while CTLA-4 binds to B7 molecules on APCs. This interaction inhibits T cell activation and proliferation, thus promoting peripheral tolerance.
**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not specifically relate to cell surface molecules involved in peripheral tolerance. While it is true that adhesion molecules are involved in immune cell interactions, they are not the primary molecules responsible for inducing tolerance.
* **Option B:** This option is incorrect because it is a type of cell surface molecule involved in cell adhesion, not tolerance. Integrins are important for immune cell migration and activation, but they do not play a direct role in peripheral tolerance.
* **Option C:** This option is incorrect because while it is a type of cell surface receptor, it is primarily involved in the activation of T cells, not tolerance. The T cell receptor (TCR) is responsible for recognizing antigens and triggering an immune response, which is the opposite of what we want for peripheral tolerance.
**Clinical Pearl / High-Yield Fact**
A key concept to remember is that peripheral tolerance is essential for preventing autoimmune diseases, and cell surface molecules like PD-L1 and CTLA-4 are critical for inducing and maintaining this tolerance. Understanding the role of these molecules can help clinicians develop new strategies for treating autoimmune diseases and cancer.
**Correct Answer:** D.