Immunological tolerance

Maizels, R.M. and Lawrence, R.A. (1991) Immunological tolerance the key feature in human filariasis Parasitology Today 7, 271-276. 

There exists direct evidence that the immune system mounts an immune response against most cancer types. Virtually all transformed cells express (a) novel surface antigens not expressed by normal cells or (b) express, at greatly elevated levels, certain antigens present normally on the cell at extremely low levels. These normal expression levels may be so low that they have gone unnoticed by immune surveillance (and thus have not induced immunological tolerance). 

The transformation of a cell to the cancerous state is normally associated with increased surface expression of antigens recognized as foreign by the host immune system. These surface antigens, often termed tumour antigens or tumour surface antigens, are either not expressed at all by the untransformed cell or are expressed at such low levels that they fail to induce immunological tolerance. 

In summary, therefore, the ability to tolerate dietary exposure to food proteins does not demand the suppression of all immune responses, but rather the avoidance or selective inhibition of immune responses of the quality required for IgE antibody production and allergic sensitization. Against this background an intriguing question relates to the nature of factors that influence the loss or failure of immunological tolerance and acquisition of allergic sensitization to food proteins, and which underlie inter-individual differences in susceptibility to food allergy [43],... 

Gershon RK, Kondo K Infectious immunological tolerance. Immunology 1971 21 903-914. 

HochweUer K, Sweenie CH, Anderton SM Immunological tolerance using synthetic peptides - basic mechanisms and clinical application. Curr Mol Med 2006 6 631-643. 

It is noteworthy that MHC class I downregulation is not the only escape mechanism available for tumors to avoid T cell responses other mechanisms such as downregulation of the tumor antigens, alterations of the apoptosis program, expression of inhibitory molecules, lack of expression of costimulatory molecules leading to immunological tolerance have been also described. The identification of defined immune escape mechanisms in human or mouse tumors point to the existence of active immunosurveillance which is important for the implementation T cell-based immunotherapy protocols. This information will further help to select patients suitable for such therapies. Furthermore, restoration of the tumor MHC class I phenotype to a normal MHC phenotype may be an other strategy to restore an efficient immune response in cancer patients. All these approaches are still hypothetical and no clinical procedures have been tested so far. 

Besides parenteral application of microspheres and nanoparticles for cell selective delivery of drugs, they have more recently been studied for their application in oral delivery of peptides and peptidomimetics [30]. Immunological tolerance induction against beta-lac-toglobulin could be achieved by application of this protein in a poly-lactic-glycolide microsphere formulation [31]. 

Korotkova, M., Telemo, E., Flanson, L. A., and Strandvik, B. (2004). Modulation of neonatal immunological tolerance to ovalbumin by maternal essential fatty acid intake. Pediatr. Allergy Immunol. 15,112-122. 

Kayhty, H., V. Karanko, H. Peltola, and P.H. Makela, Serum antibodies after vaccination with Haemophilus influenzae type b capsular polysaccharide and responses to reimmunization no evidence of immunologic tolerance or memory. Pediatrics, 1984. 74(5) 857-65. 

Immune response The development of specifically altered reactivity following exposure to an antigen. This may take several forms, e.g. antibody production, cell-mediated immunity, immunological tolerance. 

F. M. Burnet and P. Medawar Physiology/Medicine Immunological tolerance in animals... 

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