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Nyhoff LE, Clark ES, Barron BL, Bonami RH, Khan WN, Kendall PL. Bruton's Tyrosine Kinase Is Not Essential for B Cell Survival beyond Early Developmental Stages. J Immunol 2018; 200:2352-2361. [PMID: 29483358 DOI: 10.4049/jimmunol.1701489] [Citation(s) in RCA: 19] [Impact Index Per Article: 3.2] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Received: 10/25/2017] [Accepted: 01/30/2018] [Indexed: 12/21/2022]
Abstract
Bruton's tyrosine kinase (Btk) is a crucial regulator of B cell signaling and is a therapeutic target for lymphoma and autoimmune disease. BTK-deficient patients suffer from humoral immunodeficiency, as their B cells fail to progress beyond the bone marrow. However, the role of Btk in fully developed, mature peripheral B cells is not well understood. Analysis using BTK inhibitors is complicated by suboptimal inhibition, off-target effects, or failure to eliminate BTK's adaptor function. Therefore a Btkflox/Cre-ERT2 mouse model was developed and used to excise Btk after B cell populations were established. Mice lacking Btk from birth are known to have reduced follicular (FO) compartments, with expanded transitional populations, suggesting a block in development. In adult Btkflox/Cre-ERT2 mice, Btk excision did not reduce FO B cells, which persisted for weeks. Autoimmune-prone B1 cells also survived conditional Btk excision, contrasting their near absence in global Btk-deficient mice. Therefore, Btk supports BCR signaling during selection into the FO and B1 compartments, but is not needed to maintain these cell populations. B1-related natural IgM levels remained normal, contrasting global Btk deficiency, but B cell proliferation and T-independent type II immunization responses were blunted. Thus, B cells have nuanced signaling responses that are differentially regulated by Btk for development, survival, and function. These findings raise the possibility that Btk may also be expendable for survival of mature human B cells, therefore requiring prolonged dosing to be effective, and that success of BTK inhibitors may depend in part on off-target effects.
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Affiliation(s)
- Lindsay E Nyhoff
- Department of Pathology, Microbiology, and Immunology, Vanderbilt University School of Medicine, Nashville, TN 37232.,Division of Allergy, Pulmonary, and Critical Care, Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Emily S Clark
- Department of Microbiology and Immunology, Miller School of Medicine, University of Miami, Miami, FL 33136; and
| | - Bridgette L Barron
- Division of Allergy, Pulmonary, and Critical Care, Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Rachel H Bonami
- Division of Rheumatology, Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232
| | - Wasif N Khan
- Department of Microbiology and Immunology, Miller School of Medicine, University of Miami, Miami, FL 33136; and
| | - Peggy L Kendall
- Department of Pathology, Microbiology, and Immunology, Vanderbilt University School of Medicine, Nashville, TN 37232; .,Division of Allergy, Pulmonary, and Critical Care, Department of Medicine, Vanderbilt University School of Medicine, Nashville, TN 37232
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Nyhoff LE, Barron BL, Johnson EM, Bonami RH, Maseda D, Fensterheim BA, Han W, Blackwell TS, Crofford LJ, Kendall PL. Bruton's Tyrosine Kinase Deficiency Inhibits Autoimmune Arthritis in Mice but Fails to Block Immune Complex-Mediated Inflammatory Arthritis. Arthritis Rheumatol 2017; 68:1856-68. [PMID: 26945549 DOI: 10.1002/art.39657] [Citation(s) in RCA: 21] [Impact Index Per Article: 3.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 06/11/2015] [Accepted: 02/18/2016] [Indexed: 12/20/2022]
Abstract
OBJECTIVE Bruton's tyrosine kinase (BTK) is a B cell signaling protein that also contributes to innate immunity. BTK inhibitors prevent autoimmune arthritis but have off-target effects, and the mechanisms of protection remain unknown. We undertook these studies using genetic deletion to investigate the role of BTK in adaptive and innate immune responses that drive inflammatory arthritis. METHODS BTK-deficient K/BxN mice were generated to study the role of BTK in a spontaneous model that requires both adaptive and innate immunity. The K/BxN serum-transfer model was used to bypass the adaptive system and elucidate the role of BTK in innate immune contributions to arthritis. RESULTS BTK deficiency conferred disease protection to K/BxN mice, confirming outcomes of BTK inhibitors. B lymphocytes were profoundly reduced, more than in other models of BTK deficiency. Subset analysis revealed loss of B cells at all developmental stages. Germinal center B cells were also decreased, with downstream effects on numbers of follicular helper T cells and greatly reduced autoantibodies. In contrast, total IgG was only mildly decreased. Strikingly, and in contrast to small molecule inhibitors, BTK deficiency had no effect in the serum-transfer model of arthritis. CONCLUSION BTK contributes to autoimmune arthritis primarily through its role in B cell signaling and not through innate immune components.
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Affiliation(s)
| | | | | | - Rachel H Bonami
- Vanderbilt University School of Medicine, Nashville, Tennessee
| | - Damian Maseda
- Vanderbilt University School of Medicine, Nashville, Tennessee
| | | | - Wei Han
- Vanderbilt University School of Medicine, Nashville, Tennessee
| | | | | | - Peggy L Kendall
- Vanderbilt University School of Medicine, Nashville, Tennessee
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