Mutations of complement factor I and potential mechanisms of neuroinflammation in acute hemorrhagic leukoencephalitis

Abstract

Purpose: Acute Hemorrhagic Leukoencephalitis (AHLE) is a rare demyelinating disorder of acute onset, rapid deterioration and significant morbidity and mortality. Most often described as a post-infectious complication of an upper respiratory illness, its precise pathophysiology remains unclear. We describe two pediatric patients with AHLE with partial complement factor I (FI) deficiency whose successful treatment included the interleukin-1 (IL-1) receptor antagonist, anakinra, implicating a role for FI and IL-1 in this disorder.

Methods: Extensive clinical workup of two patients presenting with AHLE revealed complement abnormalities, specifically related to the alternative pathway and its regulator, FI. Aggressive management with steroids, immunoglobulin, and anakinra ultimately led to improvement of clinical status and near return to neurologic baseline in both patients. Genetic sequencing of the FI coding regions of the patients and their families was performed. In vitro protein expression studies and immunohistochemistry of fixed brain tissue was used to investigate pathogenic mechanisms.

Results: Two novel mutations in FI were identified in our patients, which result in failure to secrete FI. Immunohistochemical evaluation of brain tissue demonstrated positive staining for C3, membrane attack complex (MAC) and IL-1.

Conclusions: We propose AHLE is an unreported, rare phenotype for partial FI deficiency. The upregulation of C3, MAC and IL-1 with subsequent demyelination support a pathologic role for complement activation in AHLE, and suggest anakinra as an important adjunctive therapy in this disease.

FIG. 1. Brain imaging and biopsy

a,c, Brain MRI, Axial T2, on admission for Patient A (a) and Patient B (c). b,d, Brain MRI, Axial T2, Post-discharge. e,f, White matter with multiple foci of perivascular myelin degradation, hemorrhage, edema, and scattered infiltrating neutrophils (arrowheads), foamy macrophages and hemosiderin-laden macrophages in brain biopsies from Patient A (e) and Patient B (f). (H&E, X100)

FIG. 2. FI mutations and serum levels

Pedigrees identifying mutations in CFI and their respective serum complement factor I (FI) levels (normal 29–59 µg/mL). Probands with AHLE are indicated by arrowheads. Left, Family A. Two novel mutations identified in the CFI gene. Patient and her sister are compound heterozygotes. Right, Family B. Patient and father share the G71V mutation also found in Family A. A second coding mutation was not identified, but a noncoding or regulatory variant could also explain the markedly decreased FI serum levels

FIG. 3. Molecular modeling of CFI mutations

a, Domain structure with the positions of mutations associated with recurrent infections, aHUS, and AHLE [–, –16]. Mutations are numbered inclusive of the signal peptide (+18 relative to position numbers when the signal peptide is excluded) [13]. b, Structure of human FI [17] with AHLE mutations (red spheres) c. Structure with aHUS mutations (red spheres). Molecular images generated by PyMol [41]. FIMAC, Factor I/membrane attack complex; SRCR, scavenger receptor cysteine-rich

FIG. 4. Recombinant FI protein expression

a, Flow cytometry demonstrates similar intracellular expression of wild-type FI and mutants in transiently transfected HEK293 cells following treatment with Brefeldin A. b, Western blot of purified cell culture supernatants following transient transfection with wild-type (wt) or mutant CFI His-tagged plasmids. Images are representative of five independent experiments

FIG. 5. Histologic analysis of brain tissue

a–c, Immunohistochemistry of brain biopsy sections from Patient B demonstrating positive staining for C3 (a, X100), C5b-9 (MAC, b, X400) and IL-1 (c, X100). Arrowheads indicate positively staining cells.