| Themes > Science > Life Sciences > General Biology > Immunology > The Immune System & Disease > Tolerance > Tolerance |
Our own bodies produce some 100,000 different proteins and one of the longstanding conundrums of immunology has been to understand how the immune system produces a virtually universal repertoire while at the same time avoiding reacting to self. We can consider two different definitions of immunological tolerance. The strict definition might be that immunological tolerance occurs when an immunocompetent host fails to respond to an immunogenic challenge (ie. one that would produce a measurable response in some other, nontolerant host) with a specific antigen. A more operational definition might be that immunological tolerance occurs when an immunocompetent host fails to respond to the presence of a specific antigen. We have already seen that the adaptive immune system consists of two distinct clonally variable repertoires expressed by T and B lymphocytes respectively. Clearly the essentially random process which generates these repertoires will produce autoreactive cells in both lineages. How does the immune system prevent the activation of these cells? We can divide the mechanisms the immune system uses to ensure the absence of self-reactivity (autoimmunity) into two main types:
|
|
|