Different Complement Activation Patterns Following C5 Cleavage in MOGAD and AQP4-IgG+NMOSD.

Objectives: In myelin oligodendrocyte glycoprotein IgG-associated disease (MOGAD) and aquaporin-4 IgG+ neuromyelitis optica spectrum disorder (AQP4+NMOSD), the autoantibodies are mainly composed of IgG1, and complement-dependent cytotoxicity is a primary pathomechanism in AQP4+NMOSD. We aimed to evaluate the CSF complement activation in MOGAD.
Methods: CSF-C3a, CSF-C4a, CSF-C5a, and CSF-C5b-9 levels during the acute phase before treatment in patients with MOGAD (n = 12), AQP4+NMOSD (n = 11), multiple sclerosis (MS) (n = 5), and noninflammatory neurologic disease (n = 2) were measured.
Results: CSF-C3a and CSF-C5a levels were significantly higher in MOGAD (mean ± SD, 5,629 ± 1,079 pg/mL and 2,930 ± 435.8 pg/mL) and AQP4+NMOSD (6,017 ± 3,937 pg/mL and 2,544 ± 1,231 pg/mL) than in MS (1,507 ± 1,286 pg/mL and 193.8 ± 0.53 pg/mL). CSF-C3a, CSF-C4a, and CSF-C5a did not differ between MOGAD and AQP4+NMOSD while CSF-C5b-9 (membrane attack complex, MAC) levels were significantly lower in MOGAD (17.4 ± 27.9 ng/mL) than in AQP4+NMOSD (62.5 ± 45.1 ng/mL, p = 0.0019). Patients with MOGAD with severer attacks (Expanded Disability Status Scale [EDSS] ≥ 3.5) had higher C5b-9 levels (34.0 ± 38.4 ng/m) than those with milder attacks (EDSS ≤3.0, 0.9 ± 0.7 ng/mL, p = 0.044).
Discussion: The complement pathway is activated in both MOGAD and AQP4+NMOSD, but MAC formation is lower in MOGAD, particularly in those with mild attacks, than in AQP4+NMOSD. These findings may have pathogenetic and therapeutic implications in MOGAD.