**Core Concept**
Human leukocyte antigens (HLA) are proteins located on the surface of white blood cells that play a crucial role in the immune system's ability to distinguish between the body's own proteins and proteins made by foreign invaders, such as viruses and bacteria. The immune system's ability to recognize and respond to HLA is essential for its proper functioning.

**Why the Correct Answer is Right**
The lack of reaction to our own HLA is due to a phenomenon called **tolerance**, where the immune system learns to ignore self-antigens, including HLA, to prevent autoimmune responses. This tolerance is achieved through mechanisms such as clonal deletion, where self-reactive T cells are eliminated during their development in the thymus, and anergy, where self-reactive T cells are rendered non-functional.

**Why Each Wrong Option is Incorrect**
* **Option A:** This option is incorrect because it does not accurately describe the lack of reaction to our own HLA. While it may sound plausible, it is not a recognized medical term.
* **Option B:** This option is incorrect because it refers to a different concept in immunology, specifically the ability of the immune system to recognize and respond to antigens from other individuals. This is not relevant to the lack of reaction to our own HLA.
* **Option C:** This option is incorrect because it refers to a different concept in immunology, specifically the process by which the immune system becomes less responsive to an antigen over time. This is not relevant to the lack of reaction to our own HLA.

**Clinical Pearl / High-Yield Fact**
It's essential to remember that the immune system's ability to distinguish between self and non-self is a critical aspect of its functioning, and any disruption to this process can lead to autoimmune diseases or other immunological disorders.

**Correct Answer: D. Immune tolerance.**