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Increased expression of TACI on NOD B cells results in germinal centre reaction anomalies, enhanced plasma cell differentiation and immunoglobulin production
Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Immunology/Immunchemistry.
Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Immunology/Immunchemistry.
Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Immunology/Immunchemistry.
Umeå University, Faculty of Medicine, Department of Clinical Microbiology, Immunology/Immunchemistry.
2016 (English)In: Immunology, ISSN 0019-2805, E-ISSN 1365-2567Article in journal (Refereed) Epub ahead of print
Abstract [en]

B cells have an important pathogenic role in the development of type 1 diabetes in the non-obese diabetic (NOD) mouse. We have previously reported that NOD mice display an increased percentage of TACIhigh-expressing B cells compared with C57BL/6 mice and this trait is linked to chromosomes 1 and 8. In this paper the genetic association of the transmembrane activator, calcium modulator and cyclophilin ligand interactor (TACI) trait was confirmed using double congenic NOD.B6C1/Idd22 mice. TACI ligation by a proliferation-inducing ligand (APRIL) has been shown to influence plasma cell differentiation, immunoglobulin production and isotype switch. Hence, the functional consequence of the up-regulation of TACI on NOD B cells was analysed both in vitro and in vivo. NOD B cells stimulated with APRIL showed an enhanced plasma cell differentiation and class switch to IgG and IgA compared with B cells from C57BL/6 mice. Moreover, flow cytometry analyses revealed that germinal centre B cells in NOD failed to down-regulate TACI. Availability of the TACI ligand B-cell activating factor (BAFF) has been shown to be a limiting factor in the germinal centre reaction. In line with this, upon immunization with 4-hydroxy-3-nitrophenylacetyl hapten-conjugated hen egg lysozyme, NOD mice produced higher titres of low-affinity antibodies compared with C57BL/6 mice. This observation was supported by the detection of increased levels of BAFF in NOD germinal centres after immunization compared with C57BL/6 by immunofluorescence. Our results support the hypothesis that increased TACI expression on NOD B cells contributes to the pathogenesis of type 1 diabetes in the NOD mouse.

Place, publisher, year, edition, pages
2016.
Keyword [en]
affinity maturation, B cells, B-cell activating factor, non-obese diabetic mouse, transmembrane activat or, calcium modulator and cyclophilin ligand interactor
National Category
Microbiology in the medical area
Identifiers
URN: urn:nbn:se:umu:diva-119452DOI: 10.1111/imm.12651OAI: oai:DiVA.org:umu-119452DiVA: diva2:921021
Note

Originally published in thesis in manuscript form with the title: Increased expression of TACI in the NOD mouse results in enhanced plasma cell differentiation and immunoglobulin production

Available from: 2016-04-19 Created: 2016-04-19 Last updated: 2016-09-09
In thesis
1. Metab-Immune analysis of the non-obese diabetic mouse
Open this publication in new window or tab >>Metab-Immune analysis of the non-obese diabetic mouse
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Type 1A diabetes mellitus or T1D is a chronic disease characterized by T cell mediated destruction of the insulin producing β cells in the islets of Langerhans. The classical symptoms include high glucose levels in urine and blood, polyuria, and polydipsia. Complications associated with T1D include blindness, amputations, and end-stage renal disease, and premature death. The non-obese diabetic (NOD) mouse, first described in 1980, is widely used as a model organism for T1D. T1D disease in the NOD mouse shares a number of similarities to human T1D including dependence on genetic and environmental factors. More than 30 disease associated gene regions or loci (termed insulin dependent diabetes, or Idd, loci) have been associated with T1D development in NOD. For some of these Idds, the corresponding region in human has been linked to the development of T1D in human.

T1D, both in humans and mice, is recognized as a T cell mediated disease. However, many studies have shown the importance of both the metabolome and the immune system in the pathogenesis of the disease. Appearance of autoantibodies in the serum of patients is the first sign of pathogenesis. However, molecular and cellular events precede the immune attack on the β-cell immunity. It has been shown that patients who developed T1D have an altered metabolome prior to the appearance of autoantibodies. Although much is known about the pathogenesis of T1D, the contribution of the environment/immune factors triggering the disease is still to be revealed. 

In the present study both metabolic and immune deviations observed in the NOD mouse was analyzed. Serum metabolome analysis of the NOD mouse revealed striking resemblance to the human metabolic profile, with many metabolites in the TCA cycle significantly different from the non-diabetic control B6 mice. In addition, an increased level of glutamic acid was of the most distinguishing metabolite. A detailed bioinformatics analysis revealed various genes/enzymes to be present in the Idd regions. Compared to B6 mice, many of the genes correlated to the metabolic pathways, showed single nucleotide polymorphism (SNP), which can eventually affect the functionality of the protein. A genetic analysis of the increased glutamic acid revealed several Idd regions to be involved in this phenotype. The regions mapped in the genetic analysis harbor important enzymes and transporters related to glutamic acid. In-vitro islet culture with glutamic acid led to increased beta cell death indicating a toxic role of glutamic acid specifically towards insulin producing beta cells.

In the analysis of the immune system, B cells from NOD mice, which are known to express high levels of TACI, were stimulated with APRIL, a TACI ligand. This resulted in enhanced plasma cell differentiation accompanied with increased class switching and IgG production. NOD mice have previously been shown to react vigorously to T-dependent antigens upon immunization. In this study we confirmed this as NOD mice showed an enhanced and prolonged immune response to hen egg lysozyme. Thus, serum IgG levels were significantly increased in the NOD mice and were predominantly of the IgG1 subtype. Immunofluorescence analysis revealed increased number of germinal centers in the NOD mice. Transfer of purified B and T cells from NOD to an immune deficient mouse could reproduce the original phenotype as seen in the NOD mice.    

Collectively, this thesis has analyzed the metabolomics and immune deviations observed in the NOD mice.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2016. 62 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1777
Keyword
NOD mouse, Type 1 diabetes, B cells, glutamic acid, metabolomics
National Category
Immunology
Research subject
Immunology
Identifiers
urn:nbn:se:umu:diva-119444 (URN)978-91-7601-404-2 (ISBN)
Public defence
2016-05-13, A5_R0, Byg 6A, NUS, Umeå, 13:00 (English)
Opponent
Supervisors
Available from: 2016-04-21 Created: 2016-04-19 Last updated: 2016-04-20Bibliographically approved
2. Anomalies in humoral immunity in the NOD mouse: contribution to the progression of type 1 diabetes
Open this publication in new window or tab >>Anomalies in humoral immunity in the NOD mouse: contribution to the progression of type 1 diabetes
2016 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The non-obese diabetic (NOD) mouse is widely used model Type 1 diabetes (T1D), a chronic inflammatory disease characterized by destruction of the insulin producing β cells in the islets of Langerhans by immune cells. The classical symptoms include increased glucose levels in urine and blood, frequent urination and enhanced thirst. The disease has a strong genetic component and is also influenced by the environment. NOD mice develop T1D spontaneously. The disease occurs in two phases; insulitis - the infiltration of immune cells in the islets of Langerhans and overt diabetes caused by the destruction of insulin producing β cells. Several disease associated gene regions or loci [termed insulin dependent diabetes (Idd) loci] have been associated with T1D development. Although, T1D is recognized as a T cell mediated disease in both mouse and man, many studies have shown the importance of B cells in the pathogenesis of the disease. Autoantibodies appear prior to islet infiltration and several molecular and cellular events precede this beta-cell autoimmunity. Although the pathogenesis of T1D is well characterized, less is known about the environmental and immunological factors that trigger the disease.

In this thesis, we studied the contribution of B cell anomalies to the skewed immune response observed in the NOD mouse. In our studies covered in the thesis we observed that NOD mice display enhanced IgE in the serum already at one week of age. In addition, upon treatment of pre-diabetic NOD mice with anti-IgE antibodies, diabetes incidence was delayed. We hypothesize that the presence of IgE in the system may be explained due to enhanced class switching. Antibody feedback however, is an essential component of the immune response and can lead to either enhanced or dampened responses. Thus, increased IgE may provide positive feedback that might sustain an immune response. We also aimed to analyze the biological consequence of this feature. In vitro stimulation of B cells by the TACI ligand APRIL resulted in enhanced plasma cell differentiation accompanied with increased class switching and IgG production. In addition, TACI+ cells were observed in NOD germinal centers facilitating increased BAFF uptake and subsequent escape of low affinity antibody producing clones. NOD mice elicited an enhanced and prolonged immune response towards T-dependent antigens such as hen-egg lysozyme (HEL). Serum HEL-specific IgG level was significantly increased and was predominantly of the IgG1 isotype. Immunofluorescence analysis of NOD spleen revealed the presence of spontaneous germinal centers which others have perceived to provide a ready niche for the entry of naïve B cells that encountered novel antigen. Adoptive transfer experiments of purified B and T cells from NOD into NOD.Rag2-/- (NOD-RAG) mice illustrated the importance of B cell intrinsic defects in the reproduction of the original phenotype as observed in NOD.

Place, publisher, year, edition, pages
Umeå: Umeå University, 2016. 57 p.
Series
Umeå University medical dissertations, ISSN 0346-6612 ; 1834
Keyword
Type 1 Diabetes, NOD mouse, B cells, IgE, TACI, BAFF
National Category
Immunology in the medical area
Research subject
Immunology
Identifiers
urn:nbn:se:umu:diva-125001 (URN)978-91-7601-542-1 (ISBN)
External cooperation:
Public defence
2016-09-30, Salen - byggnad 6D, R0_A5, Målpunkt R, Umeå University, Umeå, 09:00 (English)
Opponent
Supervisors
Available from: 2016-09-09 Created: 2016-09-01 Last updated: 2016-09-09Bibliographically approved

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