This hypothesis proposes that circulating hs-CRP directly recruits CCR2+ monocytes to the CNS through upregulation of CCL2 signaling, where these infiltrating monocytes then amplify microglial IL-1β production via the TLR4/MyD88 axis, ultimately disrupting CNS immune privilege. The mechanism begins with elevated hs-CRP binding to microglial TLR4 receptors, triggering MyD88-dependent signaling that not only increases local IL-1β production but also upregulates CCL2 expression. This CCL2 gradient attracts peripheral CCR2+ monocytes across the blood-brain barrier, creating a positive feedback loop where infiltrating monocytes further enhance microglial activation and IL-1β release. The sustained presence of CCR2+ monocytes fundamentally alters the CNS immune environment, transforming the normally immunosuppressive microglial phenotype into a pro-inflammatory state that breaks down immune privilege. This dual-phase process—initial CRP-mediated microglial priming followed by monocyte-sustained amplification—explains how peripheral inflammation becomes entrenched in CNS tissue.

This hypothesis proposes that circulating hs-CRP directly recruits CCR2+ monocytes to the CNS through upregulation of CCL2 signaling, where these infiltrating monocytes then amplify microglial IL-1β production via the TLR4/MyD88 axis, ultimately disrupting CNS immune privilege. The mechanism begins with elevated hs-CRP binding to microglial TLR4 receptors, triggering MyD88-dependent signaling that not only increases local IL-1β production but also upregulates CCL2 expression. This CCL2 gradient attracts peripheral CCR2+ monocytes across the blood-brain barrier, creating a positive feedback loop where infiltrating monocytes further enhance microglial activation and IL-1β release. The sustained presence of CCR2+ monocytes fundamentally alters the CNS immune environment, transforming the normally immunosuppressive microglial phenotype into a pro-inflammatory state that breaks down immune privilege. This dual-phase process—initial CRP-mediated microglial priming followed by monocyte-sustained amplification—explains how peripheral inflammation becomes entrenched in CNS tissue. The hypothesis predicts that therapeutic interventions targeting either the CRP-TLR4 interaction or CCR2-mediated monocyte recruitment would synergistically restore CNS immune privilege by breaking the amplification cycle. This model accounts for why systemic inflammatory markers like hs-CRP correlate with neuroinflammatory diseases, while providing a mechanistic link between peripheral immune activation and CNS pathology through the CCL2/CCR2 monocyte recruitment pathway.