The hallmark autoantibodies in rheumatoid arthritis are characterized by variable domain glycans (VDGs). Their abundant occurrence results from the selective introduction of N-linked glycosylation... Show moreThe hallmark autoantibodies in rheumatoid arthritis are characterized by variable domain glycans (VDGs). Their abundant occurrence results from the selective introduction of N-linked glycosylation sites during somatic hypermutation, and their presence is predictive for disease development. However, the functional consequences of VDGs on autoreactive B cells remain elusive. Combining crystallography, glycobiology, and functional B cell assays allowed us to dissect key characteristics of VDGs on human B cell biology. Crystal structures showed that VDGs are positioned in the vicinity of the antigen-binding pocket, and dynamic modeling combined with binding assays elucidated their impact on binding. We found that VDG-expressing B cell receptors stay longer on the B cell surface and that VDGs enhance B cell activation. These results provide a rationale on how the acquisition of VDGs might contribute to the breach of tolerance of autoreactive B cells in a major human autoimmune disease. Show less
The hallmark autoantibodies in rheumatoid arthritis are characterized by variable domain glycans (VDGs). Their abundant occurrence results from the selective introduction of N-linked glycosylation... Show moreThe hallmark autoantibodies in rheumatoid arthritis are characterized by variable domain glycans (VDGs). Their abundant occurrence results from the selective introduction of N-linked glycosylation sites during somatic hyper-mutation, and their presence is predictive for disease development. However, the functional consequences of VDGs on autoreactive B cells remain elusive. Combining crystallography, glycobiology, and functional B cell assays allowed us to dissect key characteristics of VDGs on human B cell biology. Crystal structures showed that VDGs are positioned in the vicinity of the antigen-binding pocket, and dynamic modeling combined with binding assays elucidated their impact on binding. We found that VDG-expressing B cell receptors stay longer on the B cell surface and that VDGs enhance B cell activation. These results provide a rationale on how the acquisition of VDGs might contribute to the breach of tolerance of autoreactive B cells in a major human autoimmune disease. Show less
Greco, A.; Straasheijm, K.R.; Mul, K.; Heuvel, A. van den; Maarel, S.M. van der; Joosten, L.A.B.; ... ; Pruijn, G.J.M. 2021
Background: FSHD is caused by specific genetic mutations resulting in activation of the Double Homeobox 4 gene (DUX4). DUX4 targets hundreds of downstream genes eventually leading to muscle atrophy... Show moreBackground: FSHD is caused by specific genetic mutations resulting in activation of the Double Homeobox 4 gene (DUX4). DUX4 targets hundreds of downstream genes eventually leading to muscle atrophy, oxidative stress, abnormal myogenesis, and muscle inflammation. We hypothesized that DUX4-induced aberrant expression of genes triggers a sustained autoimmune response against skeletal muscle cells.Objective: This study aimed at the identification of autoantibodies directed against muscle antigens in FSHD. Moreover, a possible relationship between serum antibody reactivity and DUX4 expression was also investigated.Methods: FSHD sera (N=138, 48 +/- 16 years, 48% male) and healthy control sera (N=20, 47 +/- 14 years, 50% male) were analyzed by immunoblotting for antibodies against several skeletal muscle protein extracts: healthy muscle, FSHD muscle, healthy and FSHD myotubes, and inducible DUX4 expressing myoblasts. In addition, DUX4 expressing myoblasts were analyzed by immunofluorescence with FSHD and healthy control sera.Results: The results showed that the reactivity of FSHD sera did not significantly differ from that of healthy controls, with all the tested muscle antigen extracts. Besides, the immunofluorescent staining of DUX4-expressing myoblasts was not different when incubated with either FSHD or healthy control sera.Conclusion: Since the methodology used did not lead to the identification of disease-specific autoantibodies in the FSHD cohort, we suggest that autoantibody-mediated pathology may not be an important disease mechanism in FSHD. Nevertheless, it is crucial to further unravel if and which role the immune system plays in FSHD pathogenesis. Other innate as well as adaptive immune players could be involved in the complex DUX4 cascade of events and could become appealing druggable targets. Show less
yConclusions The vast majority of ACPA-IgG harbour N-glycans in their variable domains. As N-linked glycosylation requires glycosylation consensus sites in the protein sequence and as these are... Show moreyConclusions The vast majority of ACPA-IgG harbour N-glycans in their variable domains. As N-linked glycosylation requires glycosylation consensus sites in the protein sequence and as these are lacking in the 'germline-counterparts' of identified variable domains, our data indicate that the N-glycosylation sites in ACPA variable domains have been introduced by somatic hypermutation. This finding also suggests that ACPA-hyperglycosylation confers a selective advantage to ACPA-producing B cells. This unique and completely novel feature of the citrulline-specific immune response in RA elucidates our understanding of the underlying B cell response. Show less
Background Anti-citrullinated protein antibodies (ACPA) are the most predictive factor for the development of rheumatoid arthritis (RA). Objective To investigate whether the recognition of... Show moreBackground Anti-citrullinated protein antibodies (ACPA) are the most predictive factor for the development of rheumatoid arthritis (RA). Objective To investigate whether the recognition of citrullinated epitopes changes during disease onset or progression, by studying the fine specificity of ACPA in serum samples collected throughout the disease course, from before the onset of arthritis to longstanding RA. Methods Antibodies recognising five distinct citrullinated antigens were determined by enzyme-linked immunosorbent assay. Serum samples from 36 individuals who had donated blood before and after disease manifestation were used to investigate the development of citrullinated antigen recognition before disease onset. The association of ACPA reactivities with disease outcome was studied using sera from anti-cyclic citrullinated peptide-2 (CCP2)-positive patients with undifferentiated arthritis (UA) who did or did not progress to RA (UA-RA n = 81, or UA-UA n = 35). To investigate the ACPA recognition profile in patients with RA over a prolonged period of time, baseline serum samples from 68 patients were compared with samples obtained 7 years later. Results The number of recognised citrullinated peptides increased in the period preceding disease onset. At the time of disease manifestation, patients with UA who later developed RA recognised significantly more peptides than UA-UA patients. At later stages of the disease course, the ACPA fine specificity did not change. Conclusion Epitope spreading with an increase in the recognition of citrullinated antigens occurs before the onset of RA. Immunological differences in ACPA fine specificity between UA-UA patients and UA-RA patients are present at baseline and are associated with the future disease course. Show less
