IF low-dose intravenous immunoglobulin (IVIg; 0.4 g/kg IV) is administered to aged (10–12 month) male and female TgCRND8 or APP/PS1 transgenic mice 24–48 hours after a single session of focused ultrasound plus microbubble (FUS+MB) treatment targeting hippocampus and prefrontal cortex (220 kHz, 0.3–0.5 MPa peak negative pressure, Definity microbubbles 10 µL/kg IV), rather than at the simultaneous time point used in current protocols,

THEN amyloid plaque burden (percent area covered by Thioflavin-S+ plaques in hippocampal sections, soluble and insoluble Aβ40/42 by ELISA) will be reduced by a magnitude exceeding the 57–68% plaque reduction reported for simultaneous FUS + IVIg protocols, with a predicted target of ≥75–85% reduction, and this will be accompanied by a measurably greater density of Fc-receptor-expressing phagocytic microglia (CD68+/FcγRI+/Iba1+ cells per mm²) versus simultaneous-delivery controls,

BECAUSE the following mechanistic chain is supported by converging evidence:

1. FUS+MB treatment alone, without any antibody, mechanically activates resident microglia through acoustic radiation force and transient BBB disruption, triggering a sterile neuroinflammatory cascade that includes rapid focal IL-1β release. Sustained hippocampal IL-1β expression alone drives microglial expansion via proliferation and induces broad transcriptional changes related to immune activation — including upregulation of Fc-receptor genes (FcγRI/CD64, FcγRIII/CD16) — leading to amyloid plaque clearance in transgenic AD models (IL-1β-driven amyloid clearance is associated with transcriptionally reprogrammed microglia)[https://doi.org/10.1186/s12974-019-1645-7].

2. This FUS-induced IL-1β-driven microglial transcriptional reprogramming requires 24–48 hours to reach peak Fc-receptor surface expression. Delivering IVIg simultaneously with FUS — as in existing protocols — exposes IVIg to microglia that have not yet completed this transcriptional shift, and therefore have sub-maximal phagocytic Fc-receptor competence [SPECULATIVE — no direct study has measured Fc-receptor expression kinetics post-FUS at this temporal resolution; derived by logical extrapolation from the IL-1β priming data from https://doi.org/10.1186/s12974-019-1645-7].

3. BBB permeability following FUS+MB at these parameters remains measurably elevated for 6–24 hours and has been documented in some settings to facilitate molecular entry for up to 48 hours at lower levels; IVIg administered at 24–48 hours post-FUS therefore still enters the CNS parenchyma through the partially permeable endothelium, while encountering a microglial population now expressing peak Fc-receptor density (FUS BBB opening parameters supporting transient permeability window)[https://www.pnas.org/doi/10.1073/pnas.1908658117].

4. IVIg contains natural polyclonal anti-Aβ antibodies capable of opsonizing amyloid plaques. When these antibodies encounter Fc-receptor-upregulated microglia — primed by the preceding FUS-trigg...

SENS category: GlycoSENS

Key references: • doi.org/10.1186/s12974-019-1645-7]. • doi.org/10.1177/1533317519899800], • doi.org/10.1177/1533317519899800]. • doi.org/10.1101/2023.11.20.23298794]. • doi.org/10.1002/acn3.469].