Complement, a feature of the innate immune system that targets pathogens for phagocytic
clearance and promotes inflammation, is tightly regulated to prevent damage to host tissue. This
regulation is paramount in the central nervous system (CNS) since complement proteins degrade
neuronal synapses during development, homeostasis, and neurodegeneration. We propose that
dysregulated complement, particularly C1 or C3b, may errantly target synapses for
immune-mediated clearance, therefore highlighting regulatory failure as a major potential
mediator of neurological disease. First, we explore the mechanics of molecular neuroimmune
relationships for the regulatory proteins: Complement Receptor 1, C1-Inhibitor, Factor H, and
the CUB-sushi multiple domain family. We propose that biophysical and chemical principles offer
clues for understanding mechanisms of dysregulation. Second, we describe anticipated effects to
CNS disease processes (particularly Alzheimer's Disease) and nest our ideas within existing
basic science, clinical, and epidemiological findings. Finally, we illustrate how the concepts
presented within this manuscript provoke new ways of approaching age-old neurodegenerative
processes. Every component of this model is testable by straightforward experimentation and
highlights the untapped potential of complement dysregulation as a driver of CNS disease. This
includes a putative role for complement-based neurotherapeutic agents and companion biomarkers.
Keywords: Alzheimer's disease; C1 inhibitor; CR1; complement; factor H; neuroimmune;
schizophrenia.
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