The term extractable nuclear antigens (ENAs) is a historical denomination, though still in use, derived from the observation that several antigens from the cell nuclei are soluble and can be isolated or “extracted” in isotonic buffers, which facilitated the characterisation of several autoantibodies. Nowadays, the term has broadened and it also includes other antibodies directed against antigens from the cytoplasm and other cell compartments, such as ribonucleoproteins, histones or antigens only expressed when the cell is found in its mitotic state. Amidst this variety of autoantibodies, the anti-Ro antibodies are directed against a small intracellular RNA-protein complex, whose protein component has been described as polypeptides with molecular weights ranging from 50 to 150 kD [ [1] Ben-Chetrit E. Chan E.K.L. Sullivan K.F. Tan E.M. A 52-kD protein is a novel component of the SS-A/Ro antigenic particle. ]. The major antigenic protein is a 60 kD polypeptide (also known as Sjögren's syndrome [SS] antigen A or SSA), but other chains of different molecular weights can be also found within this complex, such as a 48 kD polypeptide (also known as SS antigen B or SSB), or a 52 kD polypeptide (also known as Ro52 or TRIM21) [ [2] The Ro small cytoplasmic ribonucleoproteins: identification of the antigenic protein and its binding site on the Ro RNAs. ]. The first two antigenic proteins, Ro/SSA and La/SSB, have traditionally been more studied than the last one, Ro52/TRIM21, possibly because historically autoantibodies to Ro52/Ro60 antigens could not be identified separately [ [1] Ben-Chetrit E. Chan E.K.L. Sullivan K.F. Tan E.M. A 52-kD protein is a novel component of the SS-A/Ro antigenic particle. , [3] Chan E.K.L. Hamel J.C. Buyon J.P. Tan E.M. Molecular definition and sequence motifs of the 52-kD component of human SS-A/Ro autoantigen. ].