IVIG interacts with human-type Aβ brain deposits in APP/PS1 mouse brain after peripheral administration. Triple immunofluorescence labelling of Aβ deposits, human IgG and microglia was performed after peripheral i.p. administration of IVIG. Aβ-immunoreactive deposits (A) and human IgG (B) was observed to co-localize in the brain parenchyma, as revealed by confocal laser-scanning microscopy imaged in the lateral entorhinal cortex (D). Human IgG was detected predominantly within Aβ plaques, but also in blood vessels (B). Human IgG-bound Aβ deposits were surrounded by Iba-1 positive microglia (C, D). Merging the immunosignals in (D) indicates that Aβ deposits were targeted both by human IgG and recruited microglia. The omission of primary antibodies resulted in the expected absence of immunolabelling.