Detection of NMO-IgG Antibodies in Thai NMO Patients Using a Recombinant E. coli AQP4-M23 ELISA

Abstract

Neuromyelitis optica (NMO) is a severe inflammatory demyelinating disorder of the CNS. NMO was usually misdiagnosed as multiple sclerosis (MS) due to their overlapping clinical features. After the discovery of NMO-IgG antibodies and its target antigen (aquaporin 4, AQP4), antibody to AQP4 (also known as AQP4-Ab or NMO-IgG) has been used as a highly specific serum marker of NMO. Objectives: To study a qualitative, indirect ELISA that uses recombinant protein of human AQP4 expressed in E. coli as an antigen for detection of anti-AQP4 antibodies in Thai NMO patients. Methods: Serum samples were obtained from 56 patients who attended the neurology clinic at Siriraj Hospital with suspected CNS demyelinating diseases. AQP4 tagged with a green fluorescent protein (GFP) was expressed in E. coli BL21(DE3)pLysS. The NMO-IgG antibodies in the patients’ sera were detected by ELISA. Crude E. coli lysates expressed AQP4-M23 isoform were used as antigens for the patients’ sera in the ELISA. Results: Detection of NMO-IgG antibodies by ELISA using synthesized recombinant AQP4-M23 antigen provides a low sensitivity (69.70%), low specificity (30.43%) test for the diagnosis of Thai NMOSDs patients. The strength of agreement was poor (kappa coefficient, k = 0.00137). The obtained ELISA data was interpreted in comparison to a CBA-Sendai. Conclusion: These results suggested that AQP4-M23-GFP fusion protein is inappropriate for detection of NMO-IgG antibodies in Thai NMO patients.