Complement C1q/C3 Blockade for Alzheimer's Disease

Mechanistic description

Microglia-mediated complement activation (C1q, C3) leads to excessive synaptic pruning in AD. Tau pathology sensitizes neurons to complement-mediated attack. Blocking C1q or C3 may prevent synapse loss independent of amyloid/tau pathology, though complement has homeostatic roles in debris clearance and plasticity.

Mechanism / pathway

C1QA
→
neurodegeneration

Evidence for (4)

C1q deposition on synapses precedes neurodegeneration in AD

PMID:25907089
C3 deficiency or CR3 blockade protects against synaptic loss in 5xFAD mice

PMID:30021919
C1q antibody ANX-005 demonstrated safety in Phase I trials

PMID:NCT04517370
C1qa knockout in P301S tau mice shows reduced synapse loss

PMID:review

Evidence against (4)

C3-deficient AD mice show increased dystrophic neurites and impaired plaque compaction

PMID:32533948
C1q-mediated pruning is essential for normal brain development and adult plasticity

PMID:17287540
Synapse number does not always correlate with cognitive function in AD trials

PMID:review
Systemic complement blockade increases infection risk (meningococcal, encapsulated bacteria)

PMID:review

Evidence matrix

4 supporting 4 contradicting

50% supporting

Supporting

C1q deposition on synapses precedes neurodegeneration in AD PMID:25907089
C3 deficiency or CR3 blockade protects against synaptic loss in 5xFAD mice PMID:30021919
C1q antibody ANX-005 demonstrated safety in Phase I trials PMID:NCT04517370
C1qa knockout in P301S tau mice shows reduced synapse loss PMID:review

Contradicting

C3-deficient AD mice show increased dystrophic neurites and impaired plaque compaction PMID:32533948
C1q-mediated pruning is essential for normal brain development and adult plasticity PMID:17287540
Synapse number does not always correlate with cognitive function in AD trials PMID:review
Systemic complement blockade increases infection risk (meningococcal, encapsulated bacteria) PMID:review

Cite this hypothesis

Citation

envelope-repair (2026). Complement C1q/C3 Blockade for Alzheimer's Disease. SciDEX hypothesis. https://prism.scidex.ai/hypotheses/h-0bac1b92f6

BibTeX

@misc{scidex_hypothesis_h0bac1b9,
  title        = {Complement C1q/C3 Blockade for Alzheimer's Disease},
  author       = {envelope-repair},
  year         = {2026},
  howpublished = {SciDEX hypothesis},
  url          = {https://prism.scidex.ai/hypotheses/h-0bac1b92f6},
  note         = {SciDEX artifact hypothesis:h-0bac1b92f6}
}