title: High Concentrations of Angiopoietin-Like Protein 4 Detected in Serum from Patients with Rheumatoid Arthritis Can Be Explained by Non-Specific Antibody Reactivity.
abstract: Angiopoietin-like protein 4 (ANGPTL4) is suggested to be a master regulator of plasma triglyceride metabolism. Our aim was to study whether the previously reported high levels of ANGPTL4 detected in serum from patients with rheumatoid arthritis (RA) by ELISA was due to any specific molecular form of this protein (oligomers, monomers or fragments). ANGPTL4 levels were first determined in serum from 68 RA patients and 43 age and sex matched control subjects and the mean values differed by a factor of 5.0. Then, ANGPTL4 was analyzed after size exclusion chromatography (SEC) of serum samples. With serum from one of the RA patients with high levels of ANGPTL4, the dominant reactivity was found in fractions corresponding to high-molecular weight proteins. In addition, a minor peak of reactivity eluting late from the column was found both in the patient and in controls. By the use of HeteroBlock®, and by careful selection of antibodies, we documented non-specific reactions for ANGPTL4 in 39% of samples from the RA patients, most likely due to cross-reactivity of the antibodies with rheumatoid factor (RF). The corresponding figure for control subjects was 6.3%. After corrections for non-specific reactions, the mean level of ANGPTL4 in serum from RA patients was still significantly higher than in control individuals (mean levels were 101±62 and 67±39 ng/ml respectively, P = 0.02). We re-analyzed samples from our previously published studies on ANGPL4 levels in patients on hemodialysis and patients with diabetes type 2. These samples did not show false positive reactions. The levels of ANGPTL4 were comparable to those detected previously.
authors.affiliation: Department of Medical Biosciences/Physiological Chemistry, Umeå University, Umeå, Sweden.
authors.forename: Elena
authors.initials: E
authors.lastname: Makoveichuk
authors.affiliation: Department of Surgery and Perioperative Sciences/Acute Medicine, Umeå University, Umeå Sweden.
authors.forename: Toralph
authors.initials: T
authors.lastname: Ruge
authors.affiliation: Department of Medical Biosciences/Physiological Chemistry, Umeå University, Umeå, Sweden.
authors.forename: Solveig
authors.initials: S
authors.lastname: Nilsson
authors.affiliation: Department of Public Health and Clinical Medicine/Rheumatology, Umeå University, Umeå, Sweden.
authors.forename: Anna
authors.initials: A
authors.lastname: Södergren
authors.affiliation: Department of Medical Biosciences/Physiological Chemistry, Umeå University, Umeå, Sweden.
authors.forename: Gunilla
authors.identifier: http://orcid.org/0000-0002-8876-6048
authors.initials: G
authors.lastname: Olivecrona
mesh_terms: D042682:Angiopoietins / Q000097:blood* / Q000276:immunology; D001172:Arthritis, Rheumatoid / Q000097:blood* / Q000276:immunology; D001323:Autoantibodies / Q000276:immunology*; D002850:Chromatography, Gel; D005260:Female; D006801:Humans; D008297:Male; D008875:Middle Aged
chemical_list: D042682:Angiopoietins; D001323:Autoantibodies; C118117:angiopoietin 4