Upregulated complement receptors correlate with Fc gamma receptor 3A-positive natural killer and natural killer-T cells in neuromyelitis optica spectrum disorder

Abstract

Background and objectives Inhibition of terminal complement in neuromyelitis optica spectrum disorder (NMOSD) using eculizumab helps prevent relapses, but the exact mechanism of action of the drug remains unclear. Similarly, genetic variants in the Fc Gamma receptor 3A (FCGR3A), also known as CD16, are correlated with outcomes in NMOSD, but the immune cells expressing those CD16 are unknown. We compared CD16 expression on immune cells modulated by complement activity in natural killer (NK) cells and natural killer-T (NKT) cells in NMOSD to disease and normal-healthy controls. Methods Peripheral blood cell (PBMC) samples from 45 patients with NMOSD with aquaporin 4 (AQP4)-IgG, 18 disease controls, and 19 normal controls were analyzed for CD16 expression and complement receptors in vitro. Results At baseline, the number of NKT cells was increased in NMOSD (p < 0.001), but the proportion that was CD16 positive was lower compared to normal and disease controls (p = 0.0012). NK cell count was normal, but the ratio that was CD16 positive was also significantly lower (p < 0.001). In both NK cells and NKT cells from NMOSD, C5 complement receptor expression was much higher than normal and disease controls (p < 0.001 for both). We also evaluated activation markers CD69 and CD83, which were also significantly higher in NK and NKT cells from NMOSD patients. FCGR3A p158 V/V genotype group in NMOSD patients showed decreased NK cell proportion with activation, and fewer CD16-expressing NKT cells than the F/F genotype group. Discussion Our results support an immunopathogenesis model in which complement pathway activation in NK/NKT cells upregulates CD16 expression that binds to antibody/antigen complexes. In the context of NMOSD, these complement-sensitive cells may be responsible for the escalating autoimmune activity.

Anti-aquaporin-4 immune complex stimulates complement-dependent Th17 cytokine release in neuromyelitis optica spectrum disorders

“…The percentage of NK cells decreased in both NMOSD groups regardless of intervention. The percentage of NKT cells tended to decrease with the addition of the AQP4-immunocomplex or total complement component as noted previously 8 . However, among those remaining NK cells, CD16 expression levels increased with AQP4-immunocomplex/complement intervention, and was more pronounced in the NMOSD group.…”

“…There is ongoing inconsistency in the literature about the prevalence of NK and NKT cells in NMOSD and other autoimmune diseases. Several previous reports have shown that the prevalence of NK/NKT cells and their CD16 expression are significantly decreased in NMOSD 5,8,25,26 . Our results here add to that finding by showing that the AQP4-immunocomplex with complement causes a further decrease of NK/NKT cells.…”

“…Flow cytometry analysis was performed as the previous report 8 . Briefly, BD Fortessa X-20 (BD Bioscience) and Cytek® Aurora (Cytek) were used for the analysis.…”

“…Beyond blocking formation of the membrane attack complex on the surface of astrocytes, complement activation is hypothesized to promote broader CNS inflammatory activity 6 . The upstream target of complement inhibition in NMOSD is not known, but NK and NKT cells are reactive to complement components and their activation in circulation 8 . These cells express both complement C3b/C4b receptor (also known as complement receptor type 1, CR1 or CD35) and C5a receptor (also known as complement component 5a receptor 1, C5aR1 or CD88), the latter of which is significantly overexpressed in people with NMOSD 8 .…”