Immune tolerance is defined as:

• A. The ability to attack all antigens
• B. The ability to ignore certain antigens
• C. The ability to respond to self antigens only
• D. The ability to respond to all pathogens

Answer: (B)

Immune tolerance is the immune system’s ability to not react to certain antigens, especially self-antigens, so the body doesn’t attack its own tissues or harmless substances. This selective ignoring is established through central tolerance (elimination of self-reactive cells during development) and peripheral tolerance (mechanisms like anergy and regulatory T cells that keep reactions in check). Because tolerance means not responding to self or harmless antigens while still recognizing and fighting real threats, the best description is the ability to ignore certain antigens. The other ideas would imply attacking all antigens, reacting only to self, or reacting to every pathogen, which isn’t how tolerance works.