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Abstract

Antibodies against citrullinated proteins are highly specific for rheumatoid arthritis (RA), but little is understood about their citrullinated target antigens. We have detected a candidate citrullinated protein by immunoblotting lysates of monocytic and granulocytic HL-60 cells treated with peptidylarginine deiminase. In an initial screen of serum samples from four patients with RA and one control, a protein of molecular mass 47 kDa from monocytic HL-60s reacted with sera from the patients, but not with the serum from the control. Only the citrullinated form of the protein was recognised. The antigen was identified by tandem mass spectrometry as α-enolase, and the positions of nine citrulline residues in the sequence were determined. Serum samples from 52 patients with RA and 40 healthy controls were tested for presence of antibodies against citrullinated and non-citrullinated α-enolase by immunoblotting of the purified antigens. Twenty-four sera from patients with RA (46%) reacted with citrullinated α-enolase, of which seven (13%) also recognised the non-citrullinated protein. Six samples from the controls (15%) reacted with both forms. α-Enolase was detected in the RA joint, where it co-localised with citrullinated proteins. The presence of antibody together with expression of antigen within the joint implicates citrullinated α-enolase as a candidate autoantigen that could drive the chronic inflammatory response in RA.

Immune-Mediated Pore-Forming Pathways Induce Cellular Hypercitrullination and Generate Citrullinated Autoantigens in Rheumatoid Arthritis

“…Since the autoantibody response in RA is directed against a limited number of specificities within the RA synovial citrullinome (8), we focused particular attention on 16 intracellular citrullinated proteins described to date, which have been confirmed to be targeted by autoantibodies in RA (Table 1) (8, 18, 25, 39–45). These included: (i) well-characterized specificities (that is, α-enolase, vimentin, collagen and histones), (ii) less well-characterized specificities (that is, actin, myeloid cell nuclear differentiation antigen, protein disulfide-isomerase, and heat shock 90kDa protein α/β) (8, 25, 43, 44), and (iii) antigens identified using granulocytes that have yet to be confirmed in the rheumatoid joint (that is, adenylyl cyclase-associated protein, aldolase, calreticulin, elongation factor 1a,60kDa heat shock protein, phosphoglycerate kinase 1, and PAD4) (40, 42, 45). Of these 16 citrullinated autoantigens, 13 were identified in RA SF cells, 14 in perforin-treated and 14 in MAC-treated cells (Table 1).…”

Antibodies to Citrullinated Vimentin are a Specific and Sensitive Marker for the Diagnosis of Rheumatoid Arthritis

“…More recently, the identification of an autoantibody against citrullinated alpha-enolase, a 47-kDa antigen abundant in RA synovium, has been published [4].…”

Human body fluid proteome analysis

“…Serum proteome analysis has revealed peptides and proteins (e.g, CRP, calgranulin A, B, and C) with diagnostic value for rheumatoid arthritis (RA) and multiple sclerosis [234][235][236][237]. Meanwhile, testing for the presence of serum autoantibodies has proven to be a confirmatory assay for autoimmune diseases [121,[238][239][240][241][242]. For instance, the serum autoantibodies against alpha-enolase were found in early RA patients, while those against actin, alphaenolase, and ATP synthase were found in celiac disease patients.…”