Abeta-induced meningoencephalitis is IFN-gamma-dependent and is associated with T cell-dependent clearance of Abeta in a mouse model of Alzheimer's disease

Abstract

Vaccination against amyloid beta-peptide (Abeta) has been shown to be successful in reducing Abeta burden and neurotoxicity in mouse models of Alzheimer's disease (AD). However, although Abeta immunization did not show T cell infiltrates in the brain of these mice, an Abeta vaccination trial resulted in meningoencephalitis in 6% of patients with AD. Here, we explore the characteristics and specificity of Abeta-induced, T cell-mediated encephalitis in a mouse model of the disease. We demonstrate that a strong Abeta-specific T cell response is critically dependent on the immunizing T cell epitope and that epitopes differ depending on MHC genetic background. Moreover, we show that a single immunization with the dominant T cell epitope Abeta10-24 induced transient meningoencephalitis only in amyloid precursor protein (APP)-transgenic (Tg) mice expressing limited amounts of IFN-gamma under an myelin basic protein (MBP) promoter. Furthermore, immune infiltrates were targeted primarily to sites of Abeta plaques in the brain and were associated with clearance of Abeta. Immune infiltrates were not targeted to the spinal cord, consistent with what was observed in AD patients vaccinated with Abeta. Using primary cultures of microglia, we show that IFN-gamma enhanced clearance of Abeta, microglia, and T cell motility, and microglia-T cell immunological synapse formation. Our study demonstrates that limited expression of IFN-gamma in the brain, as observed during normal brain aging, is essential to promote T cell-mediated immune infiltrates after Abeta immunization and provides a model to investigate both the beneficial and detrimental effects of Abeta-specific T cells.

Fig. 1.

Aβ10–24 is a highly immunogenic T cell epitope in SJL and NOD mice compared with Aβ16–30 in C57BL/6. Mice were immunized parenterally once with human Aβ1–42 and, after 10 days, lymph nodes were excised from SJL and C57BL/6 mice and analyzed for T cell proliferation induced by Aβ1–42 and 10 overlapping Aβ peptides (each of 15 residues) as described in Materials and Methods.

Fig. 2.

Immunization with the T cell epitope Aβ10–24 induces meningoencephalitis in APP/IFN-γ double Tg mice. (A) APP-Tg mice (9 months old, B6SJLF1 background) were immunized with Aβ10–24 and injected twice with PT (see Materials and Methods). Mice were killed 2 weeks later, and brain sections were analyzed by immunohistochemistry for Aβ, CD4, and MHC class II. Hematoxylin was used for counterstaining (shown in purple). High-power images show staining for Aβ, CD11b, and CD86 costimulation molecule, taken from the box shown in the Aβ Upper panel. (B–E) APP/IFN-γ Tg or single IFN-γ Tg mice were immunized with Aβ10–24 and injected with PT. At the time indicated, brain and spinal cord tissues were examined for immune infiltrates as described in Materials and Methods. (B) CD4 and CD11b immunostaining in hippocampus, cerebellum, and cortex regions of the CNS 12 days after immunization (see arrows for stained area). (C) High-power images of the meningeal area (taken from the box in B Lower) immunolabeled with antibodies to Aβ (blue), CD11b (green), and CD4 (red) and analyzed by a confocal microscope as described in Materials and Methods. (D) Aβ, CD4, and CD11b immunostaining in the hippocampus of APP/IFN-γ Tg mouse 20 days after immunization. (Lower) Higher-power versions of the circled area shown in the Upper panels. (E) Aβ, CD4, and CD11b immunostaining of spinal cord sections of APP/IFN-γ Tg mice 12 days after immunization with Aβ10–24. (F) Brain sections from nonimmunized APP and APP/IFN-γ Tg mice were immunostained with antibodies to fibrinogen. Brain sections from a mouse brain with EAE were used for a positive control staining.

Fig. 3.

Aβ10–24 immunization induced Aβ-specific Th1-type T cell proliferation and no Aβ antibodies in APP/IFN-γ Tg mice. APP/IFN-γ Tg mice were immunized with Aβ10–24, and spleen-derived T cells were analyzed in vitro for T cell proliferation, cytokine production, and Aβ antibodies on days 12, 20, and 30 after immunization as described in Materials and Methods. Representative results are shown for day 30 after immunization. (A) T cell proliferation induced by Aβ, PLP139–151, and MOG35–55 peptides and whole mouse MBP. (B) Supernatants collected from spleen-derived cultures incubated with 50 μg/ml Aβ or PLP were tested for IFN-γ, IL-10, and IL-4 production by sandwich ELISA assay. (C) Sera from APP/IFN-γ Tg or B6SJLF1 mice immunized with Aβ10–24 or human Aβ1–42, respectively, were analyzed for IgG1, IgG2a (allotypes a and b), and IgG2b Aβ antibodies. The data shown are representative results of five different experiments.

Fig. 4.

Aβ burden is decreased in hippocampus regions of APP/IFN-γ Tg mice immunized with Aβ10–24. (A) APP or APP/IFN-γ Tg mice were immunized with Aβ10–24 at 9 months of age. Six-micrometer brain sections were taken from the hippocampus and were immunolabeled for CD11b (green) and Aβ (red). TOTO-3 nuclei dye (blue) was used for counterstaining. Brain sections were analyzed by confocal microscopy as described in Materials and Methods. (Aa–Af) Two separate images and their merged image, showing the hippocampal–meningeal area of APP (Upper) and APP/IFN-γ (Lower) Tg mice taken at identical exposures. (B) Intensity representation of the Aβ and CD11b images shown in panels Aa and Ab and Ad and Ae was performed by using Zeiss lsm 510 software as described in Materials and Methods.