Exploratory proteomic analysis implicates the alternative complement cascade in primary CNS vasculitis.

OBJECTIVE: To identify molecular correlates of primary angiitis of the CNS (PACNS) through proteomic analysis of CSF from a biopsy-proven patient cohort. METHODS: Using mass spectrometry, we quantitatively compared the CSF proteome of patients with biopsy-proven PACNS (n = 8) to CSF from individuals with noninflammatory conditions (n = 11). Significantly enriched molecular pathways were identified with a gene ontology workflow, and high confidence hits within enriched pathways (fold change >1.5 and concordant Benjamini-Hochberg-adjusted p < 0.05 on DeSeq and t test) were identified as differentially regulated proteins. RESULTS: Compared to noninflammatory controls, 283 proteins were differentially expressed in the CSF of patients with PACNS, with significant enrichment of the complement cascade pathway (C4-binding protein, CD55, CD59, properdin, complement C5, complement C8, and complement C9) and neural cell adhesion molecules. A subset of clinically relevant findings were validated by Western blot and commercial ELISA. CONCLUSIONS: In this exploratory study, we found evidence of deregulation of the alternative complement cascade in CSF from biopsy-proven PACNS compared to noninflammatory controls. More specifically, several regulators of the C3 and C5 convertases and components of the terminal cascade were significantly altered. These preliminary findings shed light on a previously unappreciated similarity between PACNS and systemic vasculitides, especially anti-neutrophil cytoplasmic antibody-associated vasculitis. The therapeutic implications of this common biology and the diagnostic and therapeutic utility of individual proteomic findings warrant validation in larger cohorts.

Measurement of soluble CD59 in CSF in demyelinating disease: Evidence for an intrathecal source of soluble CD59.

BACKGROUND: CD59, a broadly expressed glycosylphosphatidylinositol-anchored protein, is the principal cell inhibitor of complement membrane attack on cells. In the demyelinating disorders, multiple sclerosis (MS) and neuromyelitis optica spectrum disorder (NMOSD), elevated complement protein levels, including soluble CD59 (sCD59), were reported in cerebrospinal fluid (CSF). OBJECTIVES: We compared sCD59 levels in CSF and matched plasma in controls and patients with MS, NMOSD and clinically isolated syndrome (CIS) and investigated the source of CSF sCD59 and whether it was microparticle associated. METHODS: sCD59 was quantified using enzyme-linked immunosorbent assay (ELISA; Hycult; HK374-02). Patient and control CSF was subjected to western blotting to characterise anti-CD59-reactive materials. CD59 was localised by immunostaining and in situ hybridisation. RESULTS: CSF sCD59 levels were double those in plasma (CSF, 30.2 ng/mL; plasma, 16.3 ng/mL). Plasma but not CSF sCD59 levels differentiated MS from NMOSD, MS from CIS and NMOSD/CIS from controls. Elimination of microparticles confirmed that CSF sCD59 was not membrane anchored. CONCLUSION: CSF levels of sCD59 are not a biomarker of demyelinating diseases. High levels of sCD59 in CSF relative to plasma suggest an intrathecal source; CD59 expression in brain parenchyma was low, but expression was strong on choroid plexus (CP) epithelium, immediately adjacent the CSF, suggesting that this is the likely source.

Increased levels of CSF CD59 in neuromyelitis optica and multiple sclerosis.

BACKGROUND: Complement activation is important in multiple sclerosis (MS) and is essential for anti-aquaporin 4 antibodies to damage the central nervous system in neuromyelitis optica (NMO). Little is known about the role of cerebrospinal fluid (CSF) regulators of complement activation in NMO and MS. We determined whether CSF CD59, which is a complement regulator and C5b-9 formation inhibitor, is involved in the pathogenesis of NMO and MS. METHODS: We analyzed CSF levels of CD59 in 30 patients with NMO, 22 patients with MS, and 24 patients with non-inflammatory neurological disorders (NINDs). Possible correlations between CSF CD59 levels and the clinical and laboratory variables in patients with NMO and MS were also reviewed. RESULTS: CSF CD59 levels in patients with NMO and MS were higher than those in patients with NINDs (p<0.001), and those in patients with NMO decreased after treatment. No significant correlations were found between CSF CD59 levels and clinical and laboratory parameters in NMO and MS. CONCLUSION: High CSF CD59 levels in NMO and MS may reflect inflammation, damage, and/or complement activation in the central nervous system.