Immunochemical property of human haptoglobin phenotypes: Determination of plasma haptoglobin using type-matched standards

Abstract

Objectives: Haptoglobin (Hp) phenotypes 1-1, 2-1, and 2-2 are associated with inflammatory diseases. Since their biochemical structures are rather heterogeneous, it is necessary to accurately determine the plasma Hp levels. Design and methods: Immunodiffusion, immunoturbidimetric, and noncompetitive ELISA were conducted to determine the differences in immunoreactivity among Hp phenotypes and to verify that such difference may significantly affect the outcome of Hp determinations. A novel ELISA using phenotype-matched calibrators was performed to compared with a commercial GenWay ELISA kit using a single calibrator in normal healthy males. Results: In immunodiffusion and immunoturbidimetric assays, the immumoreactivity of Hp 1-1 was markedly higher than 2-1 and 2-2, while an opposite result was observed using an ELISA. The latter was primarily due to the repeated antigenic epitopes in polymeric 2-1 and 2-2. Thus, Hp levels could be significantly over- or underestimated depending on the method. An accurate ELISA could be achieved when using each type-specific Hp calibrator matched to each type subject. We show the mean levels of Hp 1-1 subjects (n= 16; 184 +/- 42 mg/dL) to be significantly and differentially greater than 2-1 (n=28; 153 +/- 55 mg/dL) (p < 0.05) and 2-2 (n=24; 93 +/- 54 mg/dL) (p < 0.01) subjects. Conclusions: Due to the diverse immunochemical structure among the Hp types, phenotyping should be performed in all the patients and a type-matched Hp calibrator should be used in clinical Hp determination. (c) 2007 The Canadian Society of Clinical Chemists. Published by Elsevier Inc. All rights reserved.