Natural Autoantibodies Reactive With Glycosaminoglycansin RA
Introduction: Although natural autoantibodies make up the majority of circulating immunoglobulins and are also present in high numbers in therapeutically used intravenous immunoglobulin preparations, they have received little attention and their precise role remains largely unknown. An increasing awareness of the importance of posttranslational autoantigen modifications and glycobiology led us to explore carbohydrate-reactive natural autoantibodies in patients with rheumatoid arthritis. This study examined systematic antibodies reactive to glycosaminoglycans (GAGs), the carbohydrate components of proteoglycans that are released in large amounts from degrading cartilage.
Methods: To measure antibodies reactive to six different types of GAGs, a specialised ELISA was used in which the carbohydrates were covalently linked to the plastic surface through a 2 nm spacer. Sera from rheumatoid arthritis patients (n = 66), umbilical cord serum samples (n = 11) and adult controls (n = 54) were studied. In order to explore cross-reactivity with microbial antigens, bacterial peptidoglycans and fungal polysaccharides were used. Sera and synovial fluid samples were also tested using a GlycoChip carbohydrate array to characterise individual carbohydrate recognition patterns. We followed a multistep statistical screening strategy for screening GAG-reactive antibodies as predictive disease markers.
Results: While anti-GAG antibodies were absent in the umbilical cord sera, they were readily detectable in adult controls and were significantly elevated in patients with rheumatoid arthritis (p < 0.001). Anti-GAG antibodies showed significant cross-reactivity among different types of GAGs. They also reacted with bacterial peptidoglycans and fungal polysaccharides. Interestingly, anti-chondroitin sulphate C IgM antibody levels showed inverse correlation both with the Disease Activity Score (DAS) 28 scores and C-reactive protein (CRP) levels in rheumatoid arthritis.
Conclusion: The highly abundant and cross-reactive, GAG-specific natural autoantibodies in serum may serve as novel disease-state markers in patients with rheumatoid arthritis.
Rheumatoid arthritis (RA) is a chronic, destructive autoimmune disease of the joints, which affects about 0.5 to 1% of the population. It is characterised by the presence of autoantibodies that are reactive to various target molecules. The best known autoantibodies include rheumatoid factor (RF), anti-citrullinated protein antibodies (ACPA) and anti-collagen antibodies. Autoantibodies have attracted increasing attention recently and it is estimated that at least 50% of patients with RA have a preclinical phase associated with elevated levels of certain autoantibodies. RF, an antibody reactive to the Fc portion of IgG, has been long implicated in the pathogenesis of RA. RF is also produced during the course of the physiological response to various viral and bacterial infections and during certain inflammatory conditions, in order to help eliminate the immune complexes formed. Highly specific RFs are present in RA and may contribute to the joint inflammation, and may help B cells to take up and present various autoantigens. Both RF and ACPA are important prognostic factors in RA.
Serum IgMs are predominantly B1 B-cell-derived natural autoantibodies (NAbs). These polyreactive, low-affinity immunoglobulins are known to represent a first-line defence against infectious agents. They are also known as components of the immunological homunculus, the immune system's built-in self-representation of the body. Some NAbs recognise carbohydrates, but the role of carbohydrate-specific NAbs in RA has not been fully investigated yet.
The present study focuses on NAbs that are reactive to glycosaminoglycans (GAGs), important molecular constituents of both cell surface proteoglycans and large and small proteoglycans of the extracellular matrix of hyaline cartilage. GAGs are released from the degrading cartilage matrix in large amounts during inflammation of the joints. They are composed of repetitive disaccharide units of a hexosamine and hexuronic acid attached through a linker oligosaccharide region to the core protein of proteoglycans. A high number of GAGs are linked to the core protein of cartilage aggrecan. These negatively charged carbohydrates are responsible for the high swelling capacity of cartilage.
Our previous studies demonstrated that in Bagg Albino (BALB/c) mice, human aggrecan (partially depleted in its GAG chains) can provoke a chronic, progressive autoimmune polyarthritis (proteoglycan aggrecan-induced arthritis [PGIA]) that is similar to human RA, and the disease can be transferred to nave syngeneic mice. We have previously shown that GAG side chains play an important role in the pathogenesis of aggrecan-induced arthritis; although keratan sulphate can mask certain T-cell epitopes, chondroitin-sulphate stubs provoke a strong B-cell response and GAG-specific B cells are important antigen-presenting cells during the development of aggrecan-induced murine arthritis. A high correlation between levels of serum and synovial fluid antibodies reactive to aggrecan and biglycan has been described and may have been due to the presence of shared GAG chains of the two different proteoglycans.
To the authors' knowledge, this is the first study to describe significantly elevated anti-GAG antibody levels in sera of patients with RA and to show cross-reactivity with bacterial and fungal peptidoglycans. Our data suggest that anti-chondroitin sulphate C IgM NAbs may serve as disease-state markers of RA.
Introduction: Although natural autoantibodies make up the majority of circulating immunoglobulins and are also present in high numbers in therapeutically used intravenous immunoglobulin preparations, they have received little attention and their precise role remains largely unknown. An increasing awareness of the importance of posttranslational autoantigen modifications and glycobiology led us to explore carbohydrate-reactive natural autoantibodies in patients with rheumatoid arthritis. This study examined systematic antibodies reactive to glycosaminoglycans (GAGs), the carbohydrate components of proteoglycans that are released in large amounts from degrading cartilage.
Methods: To measure antibodies reactive to six different types of GAGs, a specialised ELISA was used in which the carbohydrates were covalently linked to the plastic surface through a 2 nm spacer. Sera from rheumatoid arthritis patients (n = 66), umbilical cord serum samples (n = 11) and adult controls (n = 54) were studied. In order to explore cross-reactivity with microbial antigens, bacterial peptidoglycans and fungal polysaccharides were used. Sera and synovial fluid samples were also tested using a GlycoChip carbohydrate array to characterise individual carbohydrate recognition patterns. We followed a multistep statistical screening strategy for screening GAG-reactive antibodies as predictive disease markers.
Results: While anti-GAG antibodies were absent in the umbilical cord sera, they were readily detectable in adult controls and were significantly elevated in patients with rheumatoid arthritis (p < 0.001). Anti-GAG antibodies showed significant cross-reactivity among different types of GAGs. They also reacted with bacterial peptidoglycans and fungal polysaccharides. Interestingly, anti-chondroitin sulphate C IgM antibody levels showed inverse correlation both with the Disease Activity Score (DAS) 28 scores and C-reactive protein (CRP) levels in rheumatoid arthritis.
Conclusion: The highly abundant and cross-reactive, GAG-specific natural autoantibodies in serum may serve as novel disease-state markers in patients with rheumatoid arthritis.
Rheumatoid arthritis (RA) is a chronic, destructive autoimmune disease of the joints, which affects about 0.5 to 1% of the population. It is characterised by the presence of autoantibodies that are reactive to various target molecules. The best known autoantibodies include rheumatoid factor (RF), anti-citrullinated protein antibodies (ACPA) and anti-collagen antibodies. Autoantibodies have attracted increasing attention recently and it is estimated that at least 50% of patients with RA have a preclinical phase associated with elevated levels of certain autoantibodies. RF, an antibody reactive to the Fc portion of IgG, has been long implicated in the pathogenesis of RA. RF is also produced during the course of the physiological response to various viral and bacterial infections and during certain inflammatory conditions, in order to help eliminate the immune complexes formed. Highly specific RFs are present in RA and may contribute to the joint inflammation, and may help B cells to take up and present various autoantigens. Both RF and ACPA are important prognostic factors in RA.
Serum IgMs are predominantly B1 B-cell-derived natural autoantibodies (NAbs). These polyreactive, low-affinity immunoglobulins are known to represent a first-line defence against infectious agents. They are also known as components of the immunological homunculus, the immune system's built-in self-representation of the body. Some NAbs recognise carbohydrates, but the role of carbohydrate-specific NAbs in RA has not been fully investigated yet.
The present study focuses on NAbs that are reactive to glycosaminoglycans (GAGs), important molecular constituents of both cell surface proteoglycans and large and small proteoglycans of the extracellular matrix of hyaline cartilage. GAGs are released from the degrading cartilage matrix in large amounts during inflammation of the joints. They are composed of repetitive disaccharide units of a hexosamine and hexuronic acid attached through a linker oligosaccharide region to the core protein of proteoglycans. A high number of GAGs are linked to the core protein of cartilage aggrecan. These negatively charged carbohydrates are responsible for the high swelling capacity of cartilage.
Our previous studies demonstrated that in Bagg Albino (BALB/c) mice, human aggrecan (partially depleted in its GAG chains) can provoke a chronic, progressive autoimmune polyarthritis (proteoglycan aggrecan-induced arthritis [PGIA]) that is similar to human RA, and the disease can be transferred to nave syngeneic mice. We have previously shown that GAG side chains play an important role in the pathogenesis of aggrecan-induced arthritis; although keratan sulphate can mask certain T-cell epitopes, chondroitin-sulphate stubs provoke a strong B-cell response and GAG-specific B cells are important antigen-presenting cells during the development of aggrecan-induced murine arthritis. A high correlation between levels of serum and synovial fluid antibodies reactive to aggrecan and biglycan has been described and may have been due to the presence of shared GAG chains of the two different proteoglycans.
To the authors' knowledge, this is the first study to describe significantly elevated anti-GAG antibody levels in sera of patients with RA and to show cross-reactivity with bacterial and fungal peptidoglycans. Our data suggest that anti-chondroitin sulphate C IgM NAbs may serve as disease-state markers of RA.