Introduction: Neuromyelitis Optica (NMO) is an inflammatory disorder affecting
the central nervous system, notably the optic nerve and spinal cord. Seropositive
NMO is marked by serum IgG antibodies against aquaporin-4 (AQP4). The
accurate identification of AQP4-IgG is crucial for distinguishing NMO from
other demyelinating diseases of the central nervous system. However, traditional
diagnostic assays have limitations in sensitivity and specificity. Here, we introduce
our in-house flow cytometry live cell-based assay (FC-LCBA) for detecting AQP4
antibodies with enhanced sensitivity and specificity. Our objective is to report the
accuracy and compare the efficacy of our newly developed in-house FC-LCBA
against the commercial cell-based indirect immunofluorescence assay (IIFA) in
detecting AQP4 antibodies.
Methods: This single-blind study was approved by the ethical committee and
involved 101 serum samples. Twenty-five samples (including retests) from 17
patients evaluated in the NMO spectrum who had at least one positive cellbased
IIFA test during the diagnosis or follow-up are tested in parallel with our
in-house FC-LCBA and cell-based IIFA. In addition, 36 serum samples from myelin
oligodendrocyte glycoprotein-associated disease (MOGAD) patients and 40 serum
samples from healthy subjects are also referred for specificity analysis.
Results: Our in-house FC-LCBA displayed superior sensitivity, detecting positive
results even when the cell-based IIFA yielded negative results in patients under
immunosuppressive treatments. Additionally, FC-LCBA exhibited high specificity
for NMO, showing negligible antibody levels in patients with MOGAD diagnosis
and healthy individuals. The assay’s stability was confirmed through consistent
results in retests.
Conclusion: Our in-house FC-LCBA emerges as a promising diagnostic tool for
detecting AQP4 antibodies, offering improved sensitivity, specificity, and reliability,
instilling confidence in its potential.
Keywords: Aquaporin-4 antibodies, flow cytometry, live cell-based assay,
neuromiyelitis optica, serological diagnosis