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Liu M, Hao M. Unique properties of IgG4 antibody and its clinical application in autoimmune pancreatitis. Scand J Gastroenterol 2018; 53:1121-1131. [PMID: 30175675 DOI: 10.1080/00365521.2018.1476915] [Citation(s) in RCA: 4] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 02/04/2023]
Abstract
BACKGROUND Autoimmune pancreatitis (AIP) is defined as a unique form of chronic pancreatitis characterized by clinical presentation with obstructive jaundice, a dense lymphoplasmacytic infiltrate and fibrosis histologically, and a dramatic response to steroids therapeutically. The possible role of IgG4 in driving the pathology of AIP is a controversial subject that has not been addressed satisfactorily. Objective: The purpose of this review is to discuss the unique biology of IgG4 that are important for its role and the clinical applications for serologic detection. METHODS Review of current literature about IgG4 antibody in the clinical application in AIP. RESULTS High serum levels of IgG4 are an important biomarker and broadly used for diagnosis, differentiation from diseases especially pancreatic cancer, and as a parameter to indicate disease activity, extra-pancreatic lesions, and treatment monitoring. However, some controversial studies show it has a limited specificity and sensitivity in these conditions. Conclusion: Although increasing studies have promoted our understanding of the structure and function of IgG4, there is still dilemma between the beneficial and the adverse aspect of IgG4 in the pathogenesis of AIP.
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Affiliation(s)
- Min Liu
- a Department of Clinical Laboratory , Jinan Dermatosis Prevention and Control Hospital , Jinan , People's Republic of China
| | - Mingju Hao
- b Department of Clinical Laboratory , Qianfo Mountain Hospital of Shandong University , Jinan , People's Republic of China
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2
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Abstract
IgG4 autoimmune diseases are characterized by the presence of antigen-specific autoantibodies of the IgG4 subclass and contain well-characterized diseases such as muscle-specific kinase myasthenia gravis, pemphigus, and thrombotic thrombocytopenic purpura. In recent years, several new diseases were identified, and by now 14 antigens targeted by IgG4 autoantibodies have been described. The IgG4 subclass is considered immunologically inert and functionally monovalent due to structural differences compared to other IgG subclasses. IgG4 usually arises after chronic exposure to antigen and competes with other antibody species, thus "blocking" their pathogenic effector mechanisms. Accordingly, in the context of IgG4 autoimmunity, the pathogenicity of IgG4 is associated with blocking of enzymatic activity or protein-protein interactions of the target antigen. Pathogenicity of IgG4 autoantibodies has not yet been systematically analyzed in IgG4 autoimmune diseases. Here, we establish a modified classification system based on Witebsky's postulates to determine IgG4 pathogenicity in IgG4 autoimmune diseases, review characteristics and pathogenic mechanisms of IgG4 in these disorders, and also investigate the contribution of other antibody entities to pathophysiology by additional mechanisms. As a result, three classes of IgG4 autoimmune diseases emerge: class I where IgG4 pathogenicity is validated by the use of subclass-specific autoantibodies in animal models and/or in vitro models of pathogenicity; class II where IgG4 pathogenicity is highly suspected but lack validation by the use of subclass specific antibodies in in vitro models of pathogenicity or animal models; and class III with insufficient data or a pathogenic mechanism associated with multivalent antigen binding. Five out of the 14 IgG4 antigens were validated as class I, five as class II, and four as class III. Antibodies of other IgG subclasses or immunoglobulin classes were present in several diseases and could contribute additional pathogenic mechanisms.
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Affiliation(s)
- Inga Koneczny
- Institute of Neurology, Medical University of Vienna, Vienna, Austria
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Koneczny I, Stevens JAA, De Rosa A, Huda S, Huijbers MG, Saxena A, Maestri M, Lazaridis K, Zisimopoulou P, Tzartos S, Verschuuren J, van der Maarel SM, van Damme P, De Baets MH, Molenaar PC, Vincent A, Ricciardi R, Martinez-Martinez P, Losen M. IgG4 autoantibodies against muscle-specific kinase undergo Fab-arm exchange in myasthenia gravis patients. J Autoimmun 2016; 77:104-115. [PMID: 27965060 DOI: 10.1016/j.jaut.2016.11.005] [Citation(s) in RCA: 81] [Impact Index Per Article: 10.1] [Reference Citation Analysis] [Abstract] [Key Words] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/19/2016] [Revised: 10/17/2016] [Accepted: 11/22/2016] [Indexed: 01/13/2023]
Abstract
Autoimmunity mediated by IgG4 subclass autoantibodies is an expanding field of research. Due to their structural characteristics a key feature of IgG4 antibodies is the ability to exchange Fab-arms with other, unrelated, IgG4 molecules, making the IgG4 molecule potentially monovalent for the specific antigen. However, whether those disease-associated antigen-specific IgG4 are mono- or divalent for their antigens is unknown. Myasthenia gravis (MG) with antibodies to muscle specific kinase (MuSK-MG) is a well-recognized disease in which the predominant pathogenic IgG4 antibody binds to extracellular epitopes on MuSK at the neuromuscular junction; this inhibits a pathway that clusters the acetylcholine (neurotransmitter) receptors and leads to failure of neuromuscular transmission. In vitro Fab-arm exchange-inducing conditions were applied to MuSK antibodies in sera, purified IgG4 and IgG1-3 sub-fractions. Solid-phase cross-linking assays were established to determine the extent of pre-existing and inducible Fab-arm exchange. Functional effects of the resulting populations of IgG4 antibodies were determined by measuring inhibition of agrin-induced AChR clustering in C2C12 cells. To confirm the results, κ/κ, λ/λ and hybrid κ/λ IgG4s were isolated and tested for MuSK antibodies. At least fifty percent of patients had IgG4, but not IgG1-3, MuSK antibodies that could undergo Fab-arm exchange in vitro under reducing conditions. Also MuSK antibodies were found in vivo that were divalent (monospecific for MuSK). Fab-arm exchange with normal human IgG4 did not prevent the inhibitory effect of serum derived MuSK antibodies on AChR clustering in C2C12 mouse myotubes. The results suggest that a considerable proportion of MuSK IgG4 could already be Fab-arm exchanged in vivo. This was confirmed by isolating endogenous IgG4 MuSK antibodies containing both κ and λ light chains, i.e. hybrid IgG4 molecules. These new findings demonstrate that Fab-arm exchanged antibodies are pathogenic.
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Affiliation(s)
- Inga Koneczny
- Department of Psychiatry and Neuropsychology, School for Mental Health and Neuroscience, Maastricht University, Universiteitssingel 50, 6229 ER Maastricht, The Netherlands
| | - Jo A A Stevens
- Department of Psychiatry and Neuropsychology, School for Mental Health and Neuroscience, Maastricht University, Universiteitssingel 50, 6229 ER Maastricht, The Netherlands
| | - Anna De Rosa
- Department of Clinical and Experimental Medicine, Neurology Unit, University of Pisa, Via Paradisa 2, 56124 Pisa, Italy
| | - Saif Huda
- Neurology Department, Nuffield Department of Clinical Neurosciences, West Wing, John Radcliffe Hospital, Oxford OX3 9DU, United Kingdom
| | - Maartje G Huijbers
- Department of Neurology, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, The Netherlands; Department of Human Genetics, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, The Netherlands
| | - Abhishek Saxena
- Department of Psychiatry and Neuropsychology, School for Mental Health and Neuroscience, Maastricht University, Universiteitssingel 50, 6229 ER Maastricht, The Netherlands
| | - Michelangelo Maestri
- Department of Clinical and Experimental Medicine, Neurology Unit, University of Pisa, Via Paradisa 2, 56124 Pisa, Italy
| | - Konstantinos Lazaridis
- Hellenic Pasteur Institute, 127 Vasilissis Sofias Avenue 115 21, Ampelokipi, Athens, Greece; Neurology Department, University Hospital, Herestraat 49, 3000 Leuven, Belgium
| | - Paraskevi Zisimopoulou
- Hellenic Pasteur Institute, 127 Vasilissis Sofias Avenue 115 21, Ampelokipi, Athens, Greece; Neurology Department, University Hospital, Herestraat 49, 3000 Leuven, Belgium
| | - Socrates Tzartos
- Hellenic Pasteur Institute, 127 Vasilissis Sofias Avenue 115 21, Ampelokipi, Athens, Greece; Neurology Department, University Hospital, Herestraat 49, 3000 Leuven, Belgium
| | - Jan Verschuuren
- Department of Neurology, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, The Netherlands
| | - Silvère M van der Maarel
- Department of Human Genetics, Leiden University Medical Center, Albinusdreef 2, 2333 ZA Leiden, The Netherlands
| | - Philip van Damme
- Neurology Department, University Hospital, Herestraat 49, 3000 Leuven, Belgium; KU Leuven - University of Leuven, Department of Neurosciences, VIB - Vesalius Research Center, Experimental Neurology - Laboratory of Neurobiology, Leuven, Belgium
| | - Marc H De Baets
- Department of Psychiatry and Neuropsychology, School for Mental Health and Neuroscience, Maastricht University, Universiteitssingel 50, 6229 ER Maastricht, The Netherlands
| | - Peter C Molenaar
- Department of Psychiatry and Neuropsychology, School for Mental Health and Neuroscience, Maastricht University, Universiteitssingel 50, 6229 ER Maastricht, The Netherlands
| | - Angela Vincent
- Neurology Department, Nuffield Department of Clinical Neurosciences, West Wing, John Radcliffe Hospital, Oxford OX3 9DU, United Kingdom
| | - Roberta Ricciardi
- Department of Clinical and Experimental Medicine, Neurology Unit, University of Pisa, Via Paradisa 2, 56124 Pisa, Italy
| | - Pilar Martinez-Martinez
- Department of Psychiatry and Neuropsychology, School for Mental Health and Neuroscience, Maastricht University, Universiteitssingel 50, 6229 ER Maastricht, The Netherlands.
| | - Mario Losen
- Department of Psychiatry and Neuropsychology, School for Mental Health and Neuroscience, Maastricht University, Universiteitssingel 50, 6229 ER Maastricht, The Netherlands.
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Hybrid kappa\lambda antibody is a new serological marker to diagnose autoimmune pancreatitis and differentiate it from pancreatic cancer. Sci Rep 2016; 6:27415. [PMID: 27271825 PMCID: PMC4897619 DOI: 10.1038/srep27415] [Citation(s) in RCA: 8] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/08/2015] [Accepted: 05/18/2016] [Indexed: 12/12/2022] Open
Abstract
The only generally accepted serological marker currently used for the diagnosis of autoimmune pancreatitis (AIP) is IgG4. Our aim was mainly to determine whether hybrid κ\λ antibody can help to diagnose AIP and to differentiate it from pancreatic cancer. We established an enzyme-linked immunosorbent assay (ELISA) system to measure the levels of hybrid κ\λ antibodies in human sera. Sera were obtained from 338 patients, including 61 with AIP, 74 with pancreatic cancer, 50 with acute pancreatitis, 40 with ordinary chronic pancreatitis, 15 with miscellaneous pancreatic diseases, and 98 with normal pancreas. Our study showed levels of hybrid κ\λ antibodies in the AIP group were significantly higher than in the non-AIP group (P < 0.001). The sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) for the diagnosis of AIP were 80.3%, 91%, 66.2% and 95.5% respectively. Furthermore, the combined measurement of serum hybrid κ\λ antibody and IgG4 tended to increase the sensitivity although the difference was not statistically significant (90.2% vs. 78.7%, P = 0.08), compared to measurement of IgG4 alone. Our findings suggest that hybrid κ\λ antibody could be a new serological marker to diagnose AIP and differentiate it from pancreatic cancer.
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