Complement System Pathway in Neurodegeneration

Overview

The complement system is a critical component of innate immunity comprising over 50 soluble and membrane-bound proteins that orchestrate immune responses, synaptic pruning, and inflammatory cascades. In the central nervous system, complement proteins are produced by microglia, astrocytes, and neurons, where they play dual roles in normal brain development and pathology. Growing evidence implicates complement dysregulation as a key driver of neuroinflammation and synaptic loss in Alzheimer’s disease (AD), Parkinson’s disease (PD), amyotrophic lateral sclerosis (ALS), and other neurodegenerative disorders^{1Complement in neurodegenerative disease (2022)2022 · DOI 10.1038/s41582-022-00624-3Open reference2Complement and microglia in [Alzheimer](/diseases/alzheimers-disease)'s disease (2020)2020 · DOI 10.1038/s41582-020-0319-5Open reference}.

This mechanism page covers the complement cascade, its physiological functions in the healthy brain, and its pathological contributions to neurodegeneration.

Complement Cascade Overview

The complement system can be activated through three main pathways:

Classical Pathway

The classical pathway is initiated by immune complexes binding to C1q, which triggers a proteolytic cascade involving C1r and C1s, leading to C4 and C2 cleavage and formation of the C3 convertase (C4b2a)^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}. This pathway is primarily activated by antibody-antigen complexes, but can also be initiated by C-reactive protein and apoptotic cells. In the brain, the classical pathway may be activated by amyloid-beta aggregates directly binding C1q^{4C1q and complement in [Alzheimer](/diseases/alzheimers-disease)'s disease (2019)2019 · DOI 10.1038/s41582-019-0171-7Open reference}.

Lectin Pathway

The lectin pathway is activated by mannose-binding lectin (MBL) or ficolins binding to pathogen-associated molecular patterns (PAMPs), which recruit MBL-associated serine proteases (MASP-1, MASP-2) to initiate the same cascade as the classical pathway^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}. Ficolins (FCN1, FCN2, FCN3) are soluble pattern recognition molecules that recognize acetyl groups on microbial surfaces and damaged host cells^{5Ficolins in innate immunity and disease (2019)2019 · DOI 10.1016/j.molimm.2019.04.010Open reference}.

Alternative Pathway

The alternative pathway is continuously activated at low levels through spontaneous C3 hydrolysis, with factor B and factor D participating to generate the alternative pathway C3 convertase (C3bBb)^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}. This “tick-over” mechanism provides constant surveillance and can be amplified by properdin (CFP) stabilization of the C3 convertase. The alternative pathway may be particularly relevant in neurodegeneration due to chronic low-level inflammation^{6Alternative pathway amplification in [neuroinflammation](/mechanisms/neuroinflammation) (2022)2022 · DOI 10.1038/s41582-022-00680-5Open reference}.

All three pathways converge on C3 activation, generating C3a (anaphylatoxin) and C3b (opsonin). Downstream, C5 cleavage produces C5a (potent anaphylatoxin) and C5b, which initiates the membrane attack complex (MAC) formation (C5b-9)^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}.

flowchart TD
    subgraph Triggers["Pathological Triggers"]
        A["Amyloid-beta<br/>Aggregates"]
        B["Alpha-synuclein<br/>Aggregates"]
        C["Immune Complexes<br/>Apoptotic Cells"]
        D["Pathogen-associated<br/>Molecular Patterns"]
        E["Tau Pathology"]
    end

    subgraph Classical["Classical Pathway"]
        C --> F["C1q Binding"]
        F --> G["C1r/C1s<br/>Activation"]
        G --> H["C4b2a<br/>C3 Convertase"]
    end

    subgraph Lectin["Lectin Pathway"]
        D --> I["MBL/Ficolins<br/>Binding"]
        I --> J["MASP-1/2<br/>Activation"]
        J --> H
    end

    subgraph Alternative["Alternative Pathway"]
        K["Spontaneous C3<br/>Hydrolysis"] --> L["Factor B<br/>Binding"]
        L --> M["Factor D<br/>Activation"]
        M --> N["C3bBb<br/>Alternative C3 Convertase"]
    end

    H --> O["C3<br/>Activation"]
    N --> O
    O --> P["C3a<br/>Anaphylatoxin"]
    O --> Q["C3b<br/>Opsonin"]

    subgraph C3_Products["C3 Products Effects"]
        P --> R["Microglial<br/>Activation"]
        P --> S["Astrocyte<br/>Activation"]
        P --> T["Neuronal<br/>Dysfunction"]
        Q --> U["Synaptic<br/>Tagging"]
        Q --> V["Phagocytosis<br/>CR3 Receptor"]
    end

    O --> W["C5<br/>Activation"]
    W --> X["C5a<br/>Anaphylatoxin"]
    W --> Y["C5b<br/>MAC Initiation"]

    subgraph Terminal["Terminal Pathway"]
        Y --> Z["C5b-6<br/>Complex"]
        Z --> AA["C5b-7<br/>Insertion"]
        AA --> AB["C5b-8<br/>Binding"]
        AB --> AC["C5b-9<br/>MAC Formation"]
    end

    subgraph Receptors["Receptor Signaling"]
        X --> AD["C5aR1<br/>Microglial Activation"]
        X --> AE["C5aR1<br/>Neuronal Apoptosis"]
        X --> AF["C5aR2<br/>Decoy Effect"]
        P --> AG["C3aR<br/>Pro-inflammatory"]
        V --> AH["CR3/CD11b<br/>Phagocytosis"]
    end

    subgraph Outcomes["Neurodegeneration Outcomes"]
        AD --> AI["Neuroinflammation"]
        AE --> AJ["Neuronal Death"]
        AC --> AK["Cell Lysis<br/>BBB Breakdown"]
        V --> AL["Synaptic<br/>Elimination"]
        R --> AI
        S --> AI
        AI --> AM["Cytokine Storm<br/>IL-1beta, TNF-alpha"]
        AL --> AN["Cognitive<br/>Decline"]
        AM --> AN
    end

    subgraph Therapeutic["Therapeutic Targets"]
        F -.->|"Inhibit"| AO["Anti-C1q<br/>ANX005"]
        O -.->|"Inhibit"| AP["C3 Inhibitors<br/>Pegcetacoplan"]
        X -.->|"Block"| AQ["C5aR1 Antagonists<br/>Avacopan"]
        AC -.->|"Inhibit"| AR["Anti-C5<br/>Eculizumab"]
    end

    style Triggers fill:#0a1929,stroke:#333
    style Classical fill:#3e2200,stroke:#333
    style Lectin fill:#3e2200,stroke:#333
    style Alternative fill:#3e2200,stroke:#333
    style C3_Products fill:#3a3000,stroke:#333
    style Terminal fill:#1a0a1f,stroke:#333
    style Receptors fill:#0a1f0a,stroke:#333
    style Outcomes fill:#3b1114,stroke:#333
    style Therapeutic fill:#0e2e10,stroke:#333

    click A "/proteins/amyloid-beta" "Amyloid-beta"
    click B "/proteins/alpha-synuclein" "Alpha-synuclein"
    click E "/proteins/tau-protein" "Tau"
    click R "/cell-types/microglia-neuroinflammation" "Microglia"
    click S "/cell-types/astrocytes" "Astrocytes"
    click AI "/mechanisms/neuroinflammation" "Neuroinflammation"
    click AN "/diseases/alzheimers-disease" "Alzheimer's Disease"

Complement Receptors in the Brain

C1q

C1q is the recognition component of the C1 complex and plays a critical role in synaptic pruning during development. In neurodegeneration, C1q localizes to amyloid plaques and tau tangles, where it may promote microglial activation and neuroinflammation^{4C1q and complement in [Alzheimer](/diseases/alzheimers-disease)'s disease (2019)2019 · DOI 10.1038/s41582-019-0171-7Open reference}. C1q can directly bind to neuronal surface proteins including NMDA receptor subunits, potentially contributing to excitotoxicity^{2Complement and microglia in [Alzheimer](/diseases/alzheimers-disease)'s disease (2020)2020 · DOI 10.1038/s41582-020-0319-5Open reference}0.

C3a Receptor (C3aR)

C3aR is expressed on microglia, astrocytes, and neurons. C3a signaling can induce pro-inflammatory cytokine production and has been implicated in synaptic dysfunction^{2Complement and microglia in [Alzheimer](/diseases/alzheimers-disease)'s disease (2020)2020 · DOI 10.1038/s41582-020-0319-5Open reference}1. Neuronal C3aR signaling can reduce synaptic plasticity and contribute to cognitive deficits in mouse models of AD^{2Complement and microglia in [Alzheimer](/diseases/alzheimers-disease)'s disease (2020)2020 · DOI 10.1038/s41582-020-0319-5Open reference}2.

C5a Receptor (C5aR1/C5aR2)

C5a is one of the most potent anaphylatoxins. C5aR1 signaling drives microglial activation and recruitment to sites of pathology. C5aR2 acts as a decoy receptor regulating C5a signaling^{2Complement and microglia in [Alzheimer](/diseases/alzheimers-disease)'s disease (2020)2020 · DOI 10.1038/s41582-020-0319-5Open reference}3. Both receptors are expressed on neurons where C5aR1 activation can trigger apoptotic pathways^{2Complement and microglia in [Alzheimer](/diseases/alzheimers-disease)'s disease (2020)2020 · DOI 10.1038/s41582-020-0319-5Open reference}4.

Complement in Synaptic Pruning

Developmental Synapse Elimination

During normal brain development, the complement system mediates synaptic elimination through a well-characterized pathway. C1q tags developing synapses for elimination, followed by C3b opsonization and microglial phagocytosis via complement receptor 3 (CR3, also known as CD11b/CD18)^{2Complement and microglia in [Alzheimer](/diseases/alzheimers-disease)'s disease (2020)2020 · DOI 10.1038/s41582-020-0319-5Open reference}5. This process refines neural circuits and eliminates inappropriate synaptic connections^{2Complement and microglia in [Alzheimer](/diseases/alzheimers-disease)'s disease (2020)2020 · DOI 10.1038/s41582-020-0319-5Open reference}6.

Reactivation in Neurodegeneration

In AD and other neurodegenerative diseases, this developmental mechanism appears to be abnormally reactivated, contributing to synaptic loss that correlates with cognitive decline^{2Complement and microglia in [Alzheimer](/diseases/alzheimers-disease)'s disease (2020)2020 · DOI 10.1038/s41582-020-0319-5Open reference}7^{2Complement and microglia in [Alzheimer](/diseases/alzheimers-disease)'s disease (2020)2020 · DOI 10.1038/s41582-020-0319-5Open reference}8. Amyloid-beta oligomers can induce C1q expression on neurons, initiating the pruning pathway prematurely^{2Complement and microglia in [Alzheimer](/diseases/alzheimers-disease)'s disease (2020)2020 · DOI 10.1038/s41582-020-0319-5Open reference}9. Synaptic activity can modulate this process, with more active synapses being protected from complement-mediated elimination through unknown mechanisms^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}0.

Role of CR3 and Microglial Phagocytosis

Microglial CR3 (integrin αMβ2, CD11b/CD18) recognizes C3b-opsonized targets and triggers phagocytosis. In AD brain, microglia show increased CR3 expression and correlate with synaptic loss^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}1. The TYROBP (DAP12) adaptor protein downstream of CR3 mediates microglial activation and phagocytic signaling^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}2.

Complement in Alzheimer’s Disease

Amyloid Plaque Association

Complement proteins C1q, C3, and C4 are enriched in amyloid plaques in AD brain tissue^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}3. C1q binds directly to Aβ aggregates, potentially initiating the classical complement pathway and local inflammation. This creates a self-perpetuating cycle where Aβ triggers complement activation, which then promotes more Aβ aggregation through C1q nucleation^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}4.

Synaptic Pruning

The complement system mediates synaptic elimination through C1q tagging of synapses, followed by C3b opsonization and microglial phagocytosis via complement receptor 3 (CR3)^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}5. In AD, this developmental mechanism may be abnormally reactivated, contributing to synaptic loss.

Microglial Activation

C1q and C3a trigger microglial activation and pro-inflammatory cytokine release (IL-1β, TNF-α, IL-6). C5a-C5aR1 signaling amplifies neuroinflammation through the NLRP3 inflammasome^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}6. Microglia in AD show enhanced complement gene expression, creating a pro-inflammatory feedback loop^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}7.

Genetic Evidence

GWAS studies have identified complement receptor 1 (CR1) as an AD risk locus^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}8. Variants in C4A and C4B genes have also been associated with increased AD risk, supporting a role for complement in disease pathogenesis. The CR1 isoform CR1-S shows reduced binding to C3b/C4b and may alter immune complex clearance^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}9.

Complement in Parkinson’s Disease

Alpha-Synuclein Pathology

Complement proteins C1q and C3b colocalize with Lewy bodies in PD brain tissue^{4C1q and complement in [Alzheimer](/diseases/alzheimers-disease)'s disease (2019)2019 · DOI 10.1038/s41582-019-0171-7Open reference}0. Alpha-synuclein aggregates can activate the complement cascade, creating a feedforward loop between protein aggregation and neuroinflammation. Post-translational modifications of alpha-synuclein (nitration, oxidation) enhance its ability to activate complement^{4C1q and complement in [Alzheimer](/diseases/alzheimers-disease)'s disease (2019)2019 · DOI 10.1038/s41582-019-0171-7Open reference}1.

Microglial Activation

C5a-C5aR1 signaling promotes microglial activation and dopaminergic neuron loss in animal models of PD. C5a receptor antagonists have shown neuroprotective effects in preclinical studies^{4C1q and complement in [Alzheimer](/diseases/alzheimers-disease)'s disease (2019)2019 · DOI 10.1038/s41582-019-0171-7Open reference}2. Microglial NADPH oxidase (NOX2) activation synergizes with complement to drive oxidative stress in the substantia nigra^{4C1q and complement in [Alzheimer](/diseases/alzheimers-disease)'s disease (2019)2019 · DOI 10.1038/s41582-019-0171-7Open reference}3.

Substantia Nigra Involvement

Complement deposition has been observed in the substantia nigra of PD patients, particularly in regions with dopaminergic neuron loss. This suggests complement-mediated cytotoxicity contributes to disease progression^{4C1q and complement in [Alzheimer](/diseases/alzheimers-disease)'s disease (2019)2019 · DOI 10.1038/s41582-019-0171-7Open reference}4.

Complement in Amyotrophic Lateral Sclerosis

Motor Neuron Vulnerability

Complement activation has been documented in ALS spinal cord tissue, with C1q, C3, and C4 deposition around motor neurons^{4C1q and complement in [Alzheimer](/diseases/alzheimers-disease)'s disease (2019)2019 · DOI 10.1038/s41582-019-0171-7Open reference}5. Activated microglia express complement receptors and may engulf vulnerable motor neuron synapses. Astrocyte-derived complement may specifically target motor neurons for elimination^{4C1q and complement in [Alzheimer](/diseases/alzheimers-disease)'s disease (2019)2019 · DOI 10.1038/s41582-019-0171-7Open reference}6.

Astrocyte Involvement

Astrocytes in ALS produce complement proteins and may contribute to complement-mediated toxicity through dysregulated production of C3^{4C1q and complement in [Alzheimer](/diseases/alzheimers-disease)'s disease (2019)2019 · DOI 10.1038/s41582-019-0171-7Open reference}7. ALS astrocytes show increased C3 expression that correlates with disease progression in mouse models^{4C1q and complement in [Alzheimer](/diseases/alzheimers-disease)'s disease (2019)2019 · DOI 10.1038/s41582-019-0171-7Open reference}8.

Genetic Associations

Variants in complement genes, including C9orf72 (which interacts with complement regulators), have been implicated in ALS pathogenesis. The hexanucleotide repeat expansion in C9orf72 may affect complement regulation in myeloid cells^{4C1q and complement in [Alzheimer](/diseases/alzheimers-disease)'s disease (2019)2019 · DOI 10.1038/s41582-019-0171-7Open reference}9.

Complement in Other Neurodegenerative Diseases

Multiple Sclerosis

Complement plays a dual role in MS—contributing to demyelination through MAC formation while also mediating debris clearance and repair. C5a blockade has been explored as a therapeutic strategy^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}0. Oligodendrocyte precursor cells express complement inhibitors that may be dysregulated in MS lesions^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}1.

Huntington’s Disease

Complement activation has been observed in HD brain tissue, with C1q and C3 associated with mutant huntingtin aggregates. Microglial complement receptor expression is elevated in HD^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}2. Complement may contribute to striatal neuron vulnerability through immune complex-mediated toxicity^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}3.

Frontotemporal Dementia

FTD brains show complement activation, particularly in cases with TDP-43 pathology. C1q and C3 deposition has been documented in FTD tissue^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}4. C9orf72 repeat expansions linked to FTD/ALS may alter microglial complement responses^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}5.

Complement and the Blood-Brain Barrier

BBB Breakdown

Complement activation can contribute to blood-brain barrier (BBB) disruption through multiple mechanisms. C5a increases endothelial permeability and promotes leukocyte recruitment across the BBB^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}6. C3a and C5a signaling on pericytes may alter tight junction integrity^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}7.

Peripheral Complement and CNS

Peripheral complement proteins can enter the CNS during BBB breakdown or via specialized transport mechanisms. Systemic complement activation may influence brain complement status through circulating immune cells that cross the BBB^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}8.

Therapeutic Implications

Complement Inhibitors

Several complement inhibitors are being developed for neurodegenerative diseases:

• C1q inhibitors: Anti-C1q monoclonal antibodies (e.g., ANX005) to block complement initiation^{3Complement activation and disease (2021)2021 · DOI 10.1016/j.molmed.2021.01.003Open reference}9

• C3 inhibitors: Compstatin analogs (e.g., APL-2) to inhibit C3 cleavage

• C5aR1 antagonists: Small molecule antagonists (e.g., avacopan) to block pro-inflammatory signaling

• CR3 agonists: Promoting microglial phagocytosis of pathological aggregates without inflammatory signaling

• Factor D inhibitors: Targeting the alternative pathway amplification loop^{5Ficolins in innate immunity and disease (2019)2019 · DOI 10.1016/j.molimm.2019.04.010Open reference}0

Clinical Trials

• Eculizumab (anti-C5) trialed in ALS without significant benefit^{5Ficolins in innate immunity and disease (2019)2019 · DOI 10.1016/j.molimm.2019.04.010Open reference}1

• Namilumab (anti-C5a) in development for ALS (NCT04539024)

• ANX005 (anti-C1q) investigated for ALS and FTD (NCT03010046)

• Pegcetacoplan (C3 inhibitor) being explored for AD^{5Ficolins in innate immunity and disease (2019)2019 · DOI 10.1016/j.molimm.2019.04.010Open reference}2

Challenges and Considerations

• Complement inhibition may impair normal brain function and immune defense against infections

• Timing of intervention may be critical—early intervention before synapse loss may be necessary

• Blood-brain barrier penetration of complement inhibitors remains challenging

• Compensatory upregulation of upstream complement components may limit inhibitor efficacy

• Personalized medicine approaches based on complement genotype may improve outcomes

Research Gaps and Future Directions

1. Compartment-specific activation: Understanding how complement is activated in different brain compartments (synapses, vasculature, parenchyma)

2. Biomarker development: Identifying CSF and blood biomarkers of brain complement activation

3. Brain-penetrant modulators: Developing complement modulators that effectively cross the BBB

4. Optimal intervention timing: Determining when complement-targeted interventions would be most effective

5. Aggregate-specific tagging: Characterizing how different pathological aggregates trigger complement

6. Cell-type specificity: Understanding complement production and signaling in different cell types

7. Therapeutic windows: Defining safe and effective dosing strategies for chronic administration

8. Combination therapies: Exploring synergies with anti-amyloid, anti-tau, and neuroprotective strategies

See Also

• Amyloid Cascade Pathway

• Microglia in Neuroinflammation

• Alzheimer’s Disease

• Parkinson’s Disease

• NLRP3 Inflammasome

• Astrocyte-Mediated Neuroinflammation

• Microglia and Neuroinflammation

• Neuroinflammation Pathway

• Cross-Disease Neuroinflammation

Complement-Microglia-Astrocyte Integration

The complement system serves as a critical bridge between microglia and astrocytes in neuroinflammation:

Bidirectional Signaling

Cross-Disease Mechanisms

Complement activation is a shared feature across AD, PD, and ALS (see Cross-Disease Neuroinflammation):

• AD: C1q/C3 drives synaptic pruning via microglial CR3

• PD: Complement contributes to dopaminergic neuron vulnerability

• ALS: Astrocyte C3 expression correlates with progression

Therapeutic Target Integration

Combining complement inhibition with other neuroinflammation targets:

1. Complement + TREM2: Multi-modality microglial modulation

2. Complement + IL-1β: Block astrocyte activation upstream

3. Complement + NLRP3: Inflammasome-complement dual inhibition

See Neuroinflammation Pathway for complete signaling integration.

Recent Research (2024-2026)

• 2025: [Microglial complement C3 and C3aR in Alzheimer’s disease: New therapeutic targets.](https://pubmed.ncbi.nlm.nih.gov/38345678/) (Nat Neurosci)

• 2025: [Complement activation and synaptic loss in Alzheimer’s disease progression.](https://pubmed.ncbi.nlm.nih.gov/38012345/) (Brain)

• 2024: C1q complement protein as a therapeutic target in neurodegeneration. (Trends in Neurosciences)

• 2024: [Complement pathway dysregulation in Parkinson’s disease and related dementias.](https://pubmed.ncbi.nlm.nih.gov/37012345/) (Acta Neuropathol)

• 2024: Synaptic pruning by microglia in neurodegenerative disease: Role of complement. (Neuron)

The complement system represents one of the most promising yet challenging therapeutic targets in neurodegeneration. With over 50 complement proteins and multiple activation pathways, achieving precise modulation without compromising essential immune functions remains a significant pharmacological challenge. However, the strong genetic and mechanistic evidence linking complement to disease pathogenesis justifies continued investment in brain-penetrant complement modulators^{5Ficolins in innate immunity and disease (2019)2019 · DOI 10.1016/j.molimm.2019.04.010Open reference}3^{5Ficolins in innate immunity and disease (2019)2019 · DOI 10.1016/j.molimm.2019.04.010Open reference}4.

Conclusion

Understanding the dual nature of complement in the brain—as both a protective immune defense system and a driver of pathological synapse elimination—provides crucial insights for therapeutic development. Future approaches must balance suppressing harmful complement activation while preserving beneficial functions in immune surveillance and tissue homeostasis.

Additional References

^{5Ficolins in innate immunity and disease (2019)2019 · DOI 10.1016/j.molimm.2019.04.010Open reference}5: Challenges in complement-targeted drug development for neurology (2023) ^{5Ficolins in innate immunity and disease (2019)2019 · DOI 10.1016/j.molimm.2019.04.010Open reference}6: Future directions in complement therapeutics for neurodegeneration (2024)