BACKGROUND: Antibodies to human neutrophil antigen (HNA)-2a are responsible for a number of immune-mediated neutropenia disorders. Although several methods exist for the identification of anti-HNA-2a, all these methods have several limitations. In this study, a solid-phase enzyme-linked immunosorbent assay (ELISA) using recombinant HNA-2a antigen (rHNA-2a) allowing rapid detection of HNA-2a antibodies was developed.
STUDY DESIGN AND METHODS: Soluble rHNA-2 was generated by transfection of insect cells with CD177 vector. Purified rHNA-2a was immobilized on microtiter wells coated with anti-CD177 and was applied to analyze 10 sera containing HNA-2a antibodies. For the evaluation of the ELISA method, results were compared with the standard assay, MAIGA (monoclonal antibody antigen capture assay) for detection of neutrophil antibodies.
RESULTS: The specificity of HNA-2a antibodies in all sera was confirmed by immunoblotting. Sera were then tested simultaneously in ELISA and MAIGA assays. Nine of 10 sera showed positive reactions in ELISA, whereas only 9 of 10 sera reacted in the standard MAIGA assay. All HNA-2a antibodies were detectable in MAIGA when diluted sera were applied. No reaction was observed with different sera containing neutrophil-reactive antibodies (6 anti-HNA-1a, 4 anti-HNA-1b, and 20 anti-HLA Class I and II) in ELISA. All HNA-2a antibodies were detectable in MAIGA when diluted sera were applied. Notably, sera containing anti-proteinase 3 (PR3) from patients with Wegener's granulomatosis reacted in MAIGA. In contrast, this antibody showed no reaction in ELISA with purified rHNA-2a.
CONCLUSIONS: These results demonstrated that ELISA with rHNA-2a provides a good method for detecting HNA-2a antibodies in human serum. This assay enables to exclude the presence of autoantibody against PR3 in patient's sera, which cannot be differentiated from anti HNA-2a with current serologic methods.