C5a complement levels in clinical remission AQP4-IgG-positive NMO patients.

Background: Neuromyelitis Optica Spectrum Disorders (NMOSD) is an antibody-mediated disorder of the Central Nervous System where a leading role of the complement system has been demonstrated.

Objective: To measure the levels of complement factors C3, C4 and C5a in serum and plasma of clinical remission patients with AQP4-IgG + NMOSD.

Methods: Twelve patients with NMOSD AQP4 + according to 2015 criteria from a General Hospital in Buenos Aires, Argentina, were included in the study, and 19 age- and sex-matched healthy volunteers as a control group (HC). AQP4 antibodies were measured in serum by CBA analysis. Fresh blood samples were centrifuged to obtain serum and plasma. C3, C4, and AQP4 antibodies were measured in the serum, whereas C5a was measured in the plasma, which was obtained using Futhan (BD FUT-175®, BD Biosciences, San Jose, CA, USA).

Results: The complement factors, C3, C4, and C5a were measured in all samples. The mean concentration of C3 was 130.7 mg/dl (SD 16.1 mg/dl), and the mean concentration of C4 was 21.6 mg/dl (SD 4.8 mg/dl); both values were within the normal reference range (C3: 84-193 mg/dl; C4: 20-40 mg/dl) and were not significantly different (p > 0.05) from the mean levels in healthy controls (C3: 116.9 mg/dl; C4: 21.9 mg/dl). When analyzing the mean plasma level of C5a, we found a statistically significant difference (p = 0.0444) between the mean concentration of C5a in NMOSD patients (43.1 ng/ml; SD 48.7 ng/ml) and the HC group (17.7 ng/ml; SD 16.7 ng/ ml).

Conclusions: In conclusion, the present study demonstrates that plasma C5a may be interesting to investigate as a potential biomarker of disease activity in NMOSD, in a larger and prospective cohort.