title: Signaling mutations and autoimmunity.
abstract: Mutations in a number of signaling components in mice can lead to strong autoimmune phenotypes. In some cases, these mutations likely compromise important feedback inhibitory pathways that downregulate antigen receptor signaling. For example, a deficiency of Lyn leads to a severe lupus-like autoimmunity. This autoimmunity may result from loss of a feedback inhibitory pathway in which Lyn phosphorylates CD22, triggering recruitment of the tyrosine phosphatase SHP-1 to the plasma membrane, which then dampens BCR signaling. Loss of Lyn also compromises an inhibitory pathway involving Fc gamma RIIb and SHIP, an inositol phosphatase. Mutation of Fyn exacerbates the autoimmunity caused by loss of Lyn. This may be due in part to a nonimmunological compromise in the integrity of the podocytes in the kidney, which may make the kidneys more susceptible to immune complex-induced damage. Fyn-deficient mice exhibit a number of immunological abnormalities and also exhibit some autoimmunity, although this is less severe than what is seen in Lyn-deficient mice. Recently a gain of function mutation in CD45 that may enhance activity of Src family tyrosine kinases has also been found to cause autoimmune disease, suggesting that the level of Src family tyrosine kinase activity is an important determinant of immune tolerance. Finally, several studies suggest that there is a significant interaction between Src family tyrosine kinases and the Fas pathway that is important for self-tolerance. Although these studies are still at an early stage, it seems clear that alterations in regulators of antigen receptor signaling can contribute to autoimmunity.
authors.affiliation: George Williams Hooper Foundation, Department of Microbiology and Immunology, University of California, San Francisco, Calif., USA.
authors.forename: Calvin C K
authors.initials: CC
authors.lastname: Yu
authors.forename: Alusha A
authors.initials: AA
authors.lastname: Mamchak
authors.forename: Anthony L
authors.initials: AL
authors.lastname: DeFranco
mesh_terms: D000818:Animals; D015703:Antigens, CD / Q000502:physiology; D000944:Antigens, Differentiation, B-Lymphocyte / Q000502:physiology; D001327:Autoimmune Diseases / Q000201:enzymology / Q000235:genetics / Q000276:immunology; D015551:Autoimmunity / Q000235:genetics / Q000276:immunology*; D015815:Cell Adhesion Molecules; D037102:Lectins / Q000502:physiology; D008180:Lupus Erythematosus, Systemic / Q000201:enzymology / Q000235:genetics / Q000276:immunology; D051379:Mice; D019463:Mice, Inbred MRL lpr; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases; D010744:Phosphoric Monoester Hydrolases / Q000502:physiology; D010766:Phosphorylation; D011499:Protein Processing, Post-Translational; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000502:physiology*; D051076:Proto-Oncogene Proteins c-fyn; D011947:Receptors, Antigen, B-Cell / Q000276:immunology; D011948:Receptors, Antigen, T-Cell / Q000276:immunology; D017463:Receptors, Complement 3b / Q000502:physiology; D017452:Receptors, IgG / Q000502:physiology; D051918:Sialic Acid Binding Ig-like Lectin 2; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology*; D019014:fas Receptor / Q000502:physiology; D019061:src-Family Kinases / Q000172:deficiency / Q000235:genetics / Q000502:physiology*
chemical_list: D015703:Antigens, CD; D000944:Antigens, Differentiation, B-Lymphocyte; C497868:Cd22 protein, mouse; D015815:Cell Adhesion Molecules; D037102:Lectins; D011518:Proto-Oncogene Proteins; D011947:Receptors, Antigen, B-Cell; D011948:Receptors, Antigen, T-Cell; D017463:Receptors, Complement 3b; D017452:Receptors, IgG; D051918:Sialic Acid Binding Ig-like Lectin 2; D019014:fas Receptor; C494960:Fyn protein, mouse; D051076:Proto-Oncogene Proteins c-fyn; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D010744:Phosphoric Monoester Hydrolases; C098706:INPPL1 protein, human; D000072183:Phosphatidylinositol-3,4,5-Trisphosphate 5-Phosphatases