Explains immune tolerance, the absence of responses to antigens the immune system could normally recognise, with emphasis on self-antigens. It covers central tolerance in the thymus and bone marrow, peripheral tolerance mechanisms, and regulatory T cells, including how they suppress immunity and the IPEX syndrome that follows FoxP3 mutation. Mnemonics such as C.P.R., A.C.I.D., I.C.E.D. and IPEX are included.
Inside: 5 sections · 12 flashcards · 9 min
Topic 56 of 105 in the MU Sofia syllabus for Biology (Medicine, Year 1). The free AceMed note covers it in 5 sections, about 1,296 words (9 min of reading), with 12 flashcards.
In this note
Definition and General Concepts
Types of Immune Tolerance
Regulatory T Lymphocytes (Tregs)
Other Mechanisms of Immune Regulation
MNEMONICS
Definition and General Concepts
Immune tolerance refers to the absence of an immune response against substances that the immune system could normally recognize as antigens.
The most important form of immune tolerance is to self-antigens. This helps prevent autoimmunity.
Individual B and T lymphocytes do not inherently distinguish between self and non-self. Each lymphocyte recognizes only one specific antigen.
True immune tolerance is an adaptive property of the immune system as a whole. It assesses antigens based on context, such as whether the antigen appears during development or in the presence of inflammation.
Some degree of discrimination exists in innate immunity. For instance, phagocytes use toll-like receptors to detect molecular patterns typical of pathogens. However, innate immunity may fail to recognize non-standard foreign substances.
Continuous Antigen Exposure and Tolerance
For immune tolerance to remain effective, the immune system must be continuously exposed to the antigen, especially during early development.
Experimental evidence in frogs showed that if an organ such as the lens is removed during development and reintroduced later, it is rejected. This is due to the lack of antigen exposure during the period when tolerance would normally develop.
Application in Transplantation: Mixed Chimerism
Mixed chimerism involves transplanting both the organ and the bone marrow from the same donor into the recipient.
The recipient’s immune system becomes a mixture of donor and host cells. These cells learn to coexist, reducing the risk of graft rejection.
This method has the potential to eliminate the need for lifelong immunosuppressive drugs by establishing long-term immune tolerance.
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