Variable domain glycosylation of ACPA-IgG: A missing link in the maturation of the ACPA response?

Pathophysiology and treatment of rheumatic disease

Fc gamma receptor binding profile of anti-citrullinated protein antibodies in immune complexes suggests a role for FcγRI in the pathogenesis of synovial inflammation

OBJECTIVES: Anti-citrullinated protein antibodies (ACPA) are highly specific for rheumatoid arthritis (RA). Here, we studied binding of ACPA-IgG immune complexes (IC) to individual Fc gamma receptors (FcγR) to identify potential effector mechanisms by which ACPA could contribute to RA pathogenesis. METHODS: ACPA-IgG1 and control IgG1(IgG1 depleted of ACPA-IgG1) were isolated from plasma and synovial fluid (SF) of RA patients by affinity chromatography using CCP2 peptides. Subsequently, IC were generated using fluorescently labelled F(ab’)2 fragments against the F(ab’)2 region of IgG, or by using citrullinated fibrinogen. IC were incubated with FcγR-transfected CHO cell lines or neutrophils from healthy donors. FcγR binding of IC was analysed by flow cytometry in the presence or absence of specific blocking antibodies. RESULTS: ACPA-IgG1 IC predominantly bound to FcγRI and FcγRIIIA on FcγR-transfected CHO cell lines, while much lower binding was observed to FcγRIIA and FcγRIIB. ACPA-IgG1 IC showed reduced binding to FcγRIIIA compared to control IgG1 IC, in line with enhanced ACPA-IgG1 Fc core-fucosylation. Neutrophils activated in vitro to induce de novo expression of FcγRI showed binding of ACPA-IgG IC, and blocking studies revealed that almost 30% of ACPA-IgG IC binding to activated neutrophils was mediated by FcγRI. CONCLUSIONS: Our studies show that ACPA-IgG1 IC bind predominately to activating FcγRI and FcγRIIIA, and highlight FcγRI expressed by activated neutrophils as relevant receptor for these IC. As neutrophils isolated from SF exhibit an activated state and express FcγRI in the synovial compartment, this IC-binding could contribute to driving disease pathogenesis in RA.Drug Delivery Technolog

The Anti-Citrullinated Protein Antibody immune response and its effector functions in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by systemic and persistent inflammation of the joints. Around 50-80% of the RA patients harbour either one or multiple types of autoantibodies, under which also Anti-Citrullinated Protein Antibodies (ACPA). ACPA are highly specific for RA and are strongly associated with the severity of arthritis. The studies described in this thesis aim to explore the structure and biological function of ACPA and the B cells producing these ACPA.The studies highlight the importance of the synovial environment for the survival of ACPA B cells. Moreover, we demonstrate that the variable region of ACPA-IgG differs from that of ACPA-IgM by the introduction of glycans, and that glycans in the constant part of antibodies can be modulated by influences from the micro-environment. This may affect the biological functions of the antibodies. Furthermore, we show that ACPA can bind to so-called Fc gamma receptor I on immune cells which could be a potential effector mechanisms of ACPA. These findings demonstrate that the structure and environment of ACPA play an important role in the ACPA immune response and provide multiple arguments for the active contribution of ACPA in the chronic inflammation of RA.LUMC / Geneeskund

The Anti-Citrullinated Protein Antibody immune response and its effector functions in Rheumatoid Arthritis

Rheumatoid arthritis (RA) is a chronic autoimmune disease characterized by systemic and persistent inflammation of the joints. Around 50-80% of the RA patients harbour either one or multiple types of autoantibodies, under which also Anti-Citrullinated Protein Antibodies (ACPA). ACPA are highly specific for RA and are strongly associated with the severity of arthritis. The studies described in this thesis aim to explore the structure and biological function of ACPA and the B cells producing these ACPA.The studies highlight the importance of the synovial environment for the survival of ACPA B cells. Moreover, we demonstrate that the variable region of ACPA-IgG differs from that of ACPA-IgM by the introduction of glycans, and that glycans in the constant part of antibodies can be modulated by influences from the micro-environment. This may affect the biological functions of the antibodies. Furthermore, we show that ACPA can bind to so-called Fc gamma receptor I on immune cells which could be a potential effector mechanisms of ACPA. These findings demonstrate that the structure and environment of ACPA play an important role in the ACPA immune response and provide multiple arguments for the active contribution of ACPA in the chronic inflammation of RA.</p

[Central congenital hypothyroidism due to Graves' disease in the mother],Centrale congenitale hypothyreo̐ưidie door ziekte van Graves bij de moeder.

Contains fulltext : 51226.pdf (publisher's version ) (Closed access)Two male twins were born at a gestational age of 30 weeks. Five days after delivery, the mother was diagnosed with Graves' disease. The thyroid function in the neonates was therefore evaluated, which led to the detection of central congenital hypothyroidism (central CHT), even though the neonatal CHT-screening had been reported to be normal. Both boys were treated with thyroxine up to the age of nine months. It was then established that their development had been uneventful. Maternal Graves' disease can, due to the presence of anti-thyroid stimulating hormone (TSH) receptor antibodies and the maternal use of anti-thyroid drugs, result in thyroid dysfunction in the neonate. Neonates born to mothers with Graves' disease are at risk of developing central CHT. This occurs especially in children of mothers who are not treated or are inadequately treated during pregnancy. In view of the importance of thyroid hormone for brain development, children with central CHT are at risk for neurodevelopmental problems if thyroid dysfunction is not detected and treated early. The Dutch screening for congenital hypothyroidism is based on thyroxine (T4), TSH and thyroid-binding globulin. This makes it possible to detect central CHT. However, in prematurely born infants this disease may be missed because in this subgroup, referral is only based on increased TSH levels, which may not be present

[Central congenital hypothyroidism due to Graves' disease in the mother]

Two male twins were born at a gestational age of 30 weeks. Five days after delivery, the mother was diagnosed with Graves' disease. The thyroid function in the neonates was therefore evaluated, which led to the detection of central congenital hypothyroidism (central CHT), even though the neonatal CHT-screening had been reported to be normal. Both boys were treated with thyroxine up to the age of nine months. It was then established that their development had been uneventful. Maternal Graves' disease can, due to the presence of anti-thyroid stimulating hormone (TSH) receptor antibodies and the maternal use of anti-thyroid drugs, result in thyroid dysfunction in the neonate. Neonates born to mothers with Graves' disease are at risk of developing central CHT. This occurs especially in children of mothers who are not treated or are inadequately treated during pregnancy. In view of the importance of thyroid hormone for brain development, children with central CHT are at risk for neurodevelopmental problems if thyroid dysfunction is not detected and treated early. The Dutch screening for congenital hypothyroidism is based on thyroxine (T4), TSH and thyroid-binding globulin. This makes it possible to detect central CHT. However, in prematurely born infants this disease may be missed because in this subgroup, referral is only based on increased TSH levels, which may not be present

Synovial fluid mononuclear cells provide an environment for long-term survival of antibody-secreting cells and promote the spontaneous production of anti-citrullinated protein antibodies

Pathophysiology and treatment of rheumatic disease

Fc gamma receptor binding profile of anti-citrullinated protein antibodies in immune complexes suggests a role for FcγRI in the pathogenesis of synovial inflammation

OBJECTIVES: Anti-citrullinated protein antibodies (ACPA) are highly specific for rheumatoid arthritis (RA). Here, we studied binding of ACPA-IgG immune complexes (IC) to individual Fc gamma receptors (FcγR) to identify potential effector mechanisms by which ACPA could contribute to RA pathogenesis. METHODS: ACPA-IgG1 and control IgG1(IgG1 depleted of ACPA-IgG1) were isolated from plasma and synovial fluid (SF) of RA patients by affinity chromatography using CCP2 peptides. Subsequently, IC were generated using fluorescently labelled F(ab’)2 fragments against the F(ab’)2 region of IgG, or by using citrullinated fibrinogen. IC were incubated with FcγR-transfected CHO cell lines or neutrophils from healthy donors. FcγR binding of IC was analysed by flow cytometry in the presence or absence of specific blocking antibodies. RESULTS: ACPA-IgG1 IC predominantly bound to FcγRI and FcγRIIIA on FcγR-transfected CHO cell lines, while much lower binding was observed to FcγRIIA and FcγRIIB. ACPA-IgG1 IC showed reduced binding to FcγRIIIA compared to control IgG1 IC, in line with enhanced ACPA-IgG1 Fc core-fucosylation. Neutrophils activated in vitro to induce de novo expression of FcγRI showed binding of ACPA-IgG IC, and blocking studies revealed that almost 30% of ACPA-IgG IC binding to activated neutrophils was mediated by FcγRI. CONCLUSIONS: Our studies show that ACPA-IgG1 IC bind predominately to activating FcγRI and FcγRIIIA, and highlight FcγRI expressed by activated neutrophils as relevant receptor for these IC. As neutrophils isolated from SF exhibit an activated state and express FcγRI in the synovial compartment, this IC-binding could contribute to driving disease pathogenesis in RA.</p