Citrullinated antigen

Citrullinated antigens are proteins that have undergone citrullination, a modification catalyzed by PAD enzymes converting arginine to citrulline[7][4]. This biochemical change can profoundly alter protein structure and function, exposing cryptic epitopes that are recognized as ‘non-self’ by the immune system, especially in RA[2][5]. Autoantibodies (ACPAs) and T cells target these neo-epitopes, leading to inflammation, joint damage, and systemic features characteristic of autoimmune diseases[1][3][8]. Citrullinated antigens are detected in patient serum or tissues, serve as biomarkers for diagnosis (most notably through ACPA or CCP assays), and underpin current research in therapeutics and diagnostics for RA and related conditions[1][6][7]. They are not a single protein target, but a class of modified self-antigens with important roles in human disease and immune regulation.

Other names

Citrullinated proteincitrullinated peptidepost-translationally modified antigencitrullinated autoantigencyclic citrullinated peptide (CCP, when referring to diagnostic motif)

For PAD inhibitors: block formation of citrullinated antigens by inhibiting the PAD enzyme For diagnostic antibodies (e.g., 12G1): selectively bind citrullinated peptide/protein motifs for detection For experimental immunotherapeutics: potential inhibition of pathogenic T-cell or antibody recognition