title: Sustained activation of Lyn tyrosine kinase in vivo leads to autoimmunity.
abstract: Genetic ablation of the Lyn tyrosine kinase has revealed unique inhibitory roles in B lymphocyte signaling. We now report the consequences of sustained activation of Lyn in vivo using a targeted gain-of-function mutation (Lyn(up/up) mice). Lyn(up/up) mice have reduced numbers of conventional B lymphocytes, down-regulated surface immunoglobulin M and costimulatory molecules, and elevated numbers of B1a B cells. Lyn(up/up) B cells are characterized by the constitutive phosphorylation of negative regulators of B cell antigen receptor (BCR) signaling including CD22, SHP-1, and SHIP-1, and display attributes of lymphocytes rendered tolerant by constitutive engagement of the antigen receptor. However, exaggerated positive signaling is also apparent as evidenced by the constitutive phosphorylation of Syk and phospholipase Cgamma2 in resting Lyn(up/up) B cells. Similarly, Lyn(up/up) B cells show a heightened calcium flux in response to BCR stimulation. Surprisingly, Lyn(up/up) mice develop circulating autoreactive antibodies and lethal autoimmune glomerulonephritis, suggesting that enhanced positive signaling eventually overrides constitutive negative signaling. These studies highlight the difficulty in maintaining tolerance in the face of chronic stimulation and emphasize the pivotal role of Lyn in B cell signaling.
authors.affiliation: Ludwig Institute for Cancer Research, Melbourne Tumour Biology Branch. Walter and Eliza Hall Institute of Medical Research, Royal Melbourne Hospital, Victoria 3050, Australia.
authors.forename: Margaret L
authors.initials: ML
authors.lastname: Hibbs
authors.forename: Kenneth W
authors.initials: KW
authors.lastname: Harder
authors.forename: Jane
authors.initials: J
authors.lastname: Armes
authors.forename: Nicole
authors.initials: N
authors.lastname: Kountouri
authors.forename: Cathy
authors.initials: C
authors.lastname: Quilici
authors.forename: Franca
authors.initials: F
authors.lastname: Casagranda
authors.forename: Ashley R
authors.initials: AR
authors.lastname: Dunn
authors.forename: David M
authors.initials: DM
authors.lastname: Tarlinton
mesh_terms: D000818:Animals; D000936:Antigen-Antibody Complex; D015703:Antigens, CD / Q000276:immunology / Q000378:metabolism; D001323:Autoantibodies / Q000097:blood; D001327:Autoimmune Diseases / Q000276:immunology / Q000473:pathology; D015551:Autoimmunity; D001402:B-Lymphocytes / Q000276:immunology / Q000378:metabolism*; D002118:Calcium / Q000378:metabolism; D002469:Cell Separation; D002478:Cells, Cultured; D004789:Enzyme Activation; D005260:Female; D005434:Flow Cytometry; D005921:Glomerulonephritis / Q000276:immunology / Q000473:pathology; D006801:Humans; D007136:Immunoglobulins / Q000276:immunology / Q000378:metabolism; D007668:Kidney / Q000276:immunology; D008198:Lymph Nodes / Q000166:cytology / Q000473:pathology; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D008822:Mice, Transgenic; D010641:Phenotype; D017354:Point Mutation; D015398:Signal Transduction; D013154:Spleen / Q000166:cytology / Q000473:pathology; D015854:Up-Regulation; D019061:src-Family Kinases / Q000235:genetics / Q000276:immunology / Q000378:metabolism*
chemical_list: D000936:Antigen-Antibody Complex; D015703:Antigens, CD; D001323:Autoantibodies; D007136:Immunoglobulins; C060902:lyn protein-tyrosine kinase; D019061:src-Family Kinases; D002118:Calcium