Internal and Emergency Medicine

, Volume 1, Issue 3, pp 187–196 | Cite as

Immunological tolerance and autoimmunity

  • Sergio RomagnaniEmail author
Internal Medicine Review Article Clinical Immunology


Immunological tolerance is a complex series of mechanisms that impair the immune system to mount responses against self antigens. Central tolerance occurs when immature lymphocytes encounter self antigens in the primary lymphoid organs, and consequently they die or become unreactive. Peripheral tolerance occurs when mature lymphocytes, escaped from negative selection during ontogeny, encounter self antigens in secondary lymphoid organs and undergo anergy, deletion or suppression. A heterogeneous family of T regulatory cells has recently been identified, which have been found to play an important role in suppressing immune responses against self. Failure or breakdown of immunological tolerance results in autoimmunity and autoimmune diseases. Such events are related to both genetic and environmental factors, the latter being mainly represented by infections. Infectious agents can indeed promote autoimmune responses either by inducing tissue inflammation and therefore an uninten ded bystander activation of autoreactive T cells, or by promoting T cell responses to microbial epitopes that cross react against self peptides.

Key words

by-stander activation central tolerance molecular mimicry peripheral tolerance promiscuous gene expression Treg cells 


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Copyright information

© SIMI, Italian Society of Internal Medicine 2006

Authors and Affiliations

  1. 1.Department of Internal Medicine, Excellence Centre DenotheUniversity of FlorenceFlorenceItaly

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