Characterization of the binding pattern of human aquaporin-4 autoantibodies in patients with neuromyelitis optica spectrum disorders.

J Neuroinflammation 2016 07 1;13(1):176. Epub 2016 Jul 1.

Clinical Department of Neurology, Medical University of Innsbruck, Innsbruck, Austria.

Background: The discovery of a highly specific antibody against the aquaporin-4 (AQP4) water channel (AQP4-IgG) unified the spectrum of neuromyelitis optica spectrum disorders (NMOSD), which are considered to be antibody-mediated autoimmune diseases. The AQP4 water channel is located on astrocytic end-feet processes and consists of six transmembrane helical domains forming three extracellular loops A, C, and E in which defined amino acids were already proven to be critical for AQP4-IgG binding. However, the clinical relevance of these findings is unclear. Therefore, we have characterized the epitope specificity of AQP4-IgG-positive NMOSD patients.

Methods: We established a cell-based flow cytometry assay for the quantitative detection of AQP4-IgG-positive serum samples. Human embryonic kidney (HEK) cells were transiently transfected with an EmGFP-tagged AQP4-M23, AQP4-M1, or six AQP4-M23 extracellular loop mutants including two mutations in loop A (serial AA substitution, insertion of a myc-tag), two in loop C (N153Q, insertion of a myc-tag), and two in loop E (H230G, insertion of a myc-tag). Fourty-seven baseline and 49 follow-up serum samples and six paired cerebrospinal fluid (CSF) baseline samples of 47 AQP4-IgG-positive Austrian NMOSD patients were then tested for their binding capability to AQP4-M1 and AQP4-M23 isoforms and these six extracellular loop mutants.

Results: Overall, we could identify two broad patterns of antibody recognition based on differential sensitivity to mutations in extracellular loop A. Pattern A was characterized by reduced binding to the two mutations in loop A, whereas pattern B had only partial or no reduced binding to these mutations. These two patterns were not associated with significant differences in demographic and clinical parameters or serum titers in this retrospective study. Interestingly, we found a change of AQP4-IgG epitope recognition pattern in seven of 20 NMOSD patients with available follow-up samples. Moreover, we found different binding patterns in five of six paired CSF versus serum samples, with a predominance of pattern A in CSF.

Conclusions: Our study demonstrates that AQP4-IgG in sera of NMOSD patients show distinct patterns of antibody recognition. The clinical and diagnostic relevance of these findings have to be addressed in prospective studies.

Download full-text PDF

Source
http://dx.doi.org/10.1186/s12974-016-0642-3DOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4930584PMC
July 2016
45 Reads

Publication Analysis

Top Keywords

serum samples
12
insertion myc-tag
12
extracellular loop
12
nmosd patients
12
binding mutations
8
reduced binding
8
aqp4 water
8
spectrum disorders
8
water channel
8
aqp4-m1 aqp4-m23
8
mutations loop
8
myc-tag loop
8
patterns antibody
8
optica spectrum
8
antibody recognition
8
loop pattern
8
relevance findings
8
neuromyelitis optica
8
loop
7
pattern
5

References

(Supplied by CrossRef)

DM Wingerchuk et al.
Neurology 1999

VA Lennon et al.
Lancet 2004

DM Wingerchuk et al.
Neurology 2015

M Bradl et al.
Ann Neurol 2009

JL Bennett et al.
Ann Neurol 2009

S Saadoun et al.
Ann Neurol 2012

H Zhang et al.
J Clin Invest 2013

S Nielsen et al.
J Neurosci 1997

JE Rash et al.
Proc Natl Acad Sci U S A 1998

J Li et al.
Invest Ophthalmol Vis Sci 2002

DJ Graber et al.
J Neuroinflammation 2008

Similar Publications