IVIg treatment decreases Aβ42/Aβ40 ratio and 56 kDa Aβ oligomers. (A) Human Aβ40 and Aβ42 peptides were quantified using specific ELISA in parietotemporal cortex homogenates of 3xTg-AD mice. Aβ concentrations in soluble and insoluble fractions remained unchanged following IVIg injections in 12-month-old (3-month treatment, n = 11 to 13 mice) and 16-month-old 3xTg-AD mice at sacrifice (pooled 1- and 3-month-treatment duration, n = 25 animals). The Aβ42/Aβ40 ratio was significantly decreased in the soluble fraction of 16-month-old IVIg-treated mice. (B) Aβ deposition was analyzed in the hippocampus after immunohistochemistry using 6E10 antibody in NonTg and 3xTg-AD mice. 20× magnification. Right: graph shows the quantification of the area occupied by extracellular amyloid plaques in four consecutive brain sections of the subiculum of the hippocampal formation from 12-month-old 3xTg-AD mice treated for 3 months with IVIg or vehicle (n = 11 per group). Red, human APP; blue, hematoxylin counterstain. (C) The expression of transgenic human APP (membrane fraction) and the soluble αAPP fragment and Aβ*56 oligomers (cytosolic fraction) were quantified by Western blot analysis with 6E10 antibody in the cortex of 12- and 16-month-old mice treated for 3 months with IVIg (n = 13 animals) or vehicle (n = 12 to 14 animals). Significant reduction of soluble Aβ*56 oligomers was also observed on IVIg treatment. Examples of immunoblots are shown for both fractions (bottom right). Values are expressed as mean ± SEM. Statistical analysis: unpaired Student t-test with Welch’s correction. *P <0.05, **P <0.01, ***P <0.001 versus vehicle-treated 3xTg-AD mice. 3xTg-AD, triple-transgenic mouse model of Alzheimer’s disease; APP, amyloid precursor protein; C, control; ctrl, control; ELISA, enzyme-linked immunosorbent assay; I, human intravenous immunoglobulin; IVIg, human intravenous immunoglobulin; NonTg, non-transgenic; NTg, non-transgenic; RLU, relative luminescence unit.