Structural, immunological and functional comparisons of factor H, rheumatoid arthritis protein (RHP), and its apparent normal counterpart (N-RHP)

• Published in: Molecular immunology 1995-11, Vol.32 (16), p.1259-1269
• Main Authors: Hurwitz, Charles, Rosano, Carmen L., Hechemy, Karim E., Weber, Peter, Parhami, Nourollah
• Format: Article
• Language: English
• Subjects: Amino Acids - analysis; Animals; Blood Proteins - chemistry; Blood Proteins - immunology; Blood Proteins - metabolism; Complement Activating Enzymes - immunology; Complement Activating Enzymes - metabolism; Complement Factor H - chemistry; Complement Factor H - immunology; Complement Factor H - metabolism; complement system; Complement System Proteins - immunology; Complement System Proteins - metabolism; Epitopes - immunology; Factor H; Humans; Rabbits; rheumatoid arthritis protein; RHP
• ISSN: 0161-5890; 1872-9142
• DOI: 10.1016/0161-5890(95)00068-2

The isolation and characterization of two human serum proteins, RHP and N-RHP, are described. N-RHP appears to be the normal counterpart of RHP which is found at elevated levels in sera of patients with rheumatoid arthritis [Rosano et al. (1988 b) Inflammation 12, 351–360]. Although both proteins crossreact with anti-Factor H and have identical N-terminal amino acid sequences, they differ from Factor H in pI, solubility at low ionic strength, and in glycosylation. RHP differs from Factor H and N-RHP in antigenicity in the rabbit, in effect on the C1q-anti-C1q precipitin reaction, and in ability to disaggregate C1, the first component of the complement system. Removal of RHP, N-RHP and Factor H from binding to C1q is a prerequesite for separation of RHP and N-RHP from Factor H by anion exchange chromatography and isoelectric focusing. The finding of uniquely demonstrable RHP activity (enhancement of C1q-anti-C1q precipitin activity) in unfractionated sera from patients with rheumatoid arthritis, but not in normal sera, suggests that RHP is not an artefact of Factor H produced during isolation.