Inhibitory NK-cell receptor (purple and light blue) binds to MHC-I (blue and red), an interaction that prevents immune responses against self.Credit: NIAID
Tolerance is the prevention of an immune response against a particular antigen. For instance, the immune system is generally tolerant of self-antigens, so it does not usually attack the body's own cells, tissues, and organs. However, when tolerance is lost, disorders like autoimmune disease or food allergy may occur. Tolerance is maintained in a number of ways:
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Fetomaternal tolerance is the prevention of a maternal immune response against a developing fetus. Major histocompatibility complex (MHC) proteins help the immune system distinguish between host and foreign cells. MHC also is called human leukocyte antigen (HLA). By expressing paternal MHC or HLA proteins and paternal antigens, a fetus can potentially trigger the mother's immune system. However, there are several barriers that may prevent this from occurring: The placenta reduces the exposure of the fetus to maternal immune cells, the proteins expressed on the outer layer of the placenta may limit immune recognition, and regulatory cells and suppressive signals may play a role.
Read more about MHC proteins in Communication.
Transplantation of a donor tissue or organ requires appropriate MHC or HLA matching to limit the risk of rejection. Because MHC or HLA matching is rarely complete, transplant recipients must continuously take immunosuppressive drugs, which can cause complications like higher susceptibility to infection and some cancers. Researchers are developing more targeted ways to induce tolerance to transplanted tissues and organs while leaving protective immune responses intact.
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Last Updated January 17, 2014