Eric M. Reiman

INTRODUCTION: While there may be microbial contributions to Alzheimer’s disease (AD), findings have been inconclusive. We recently reported an AD-associated CD83(+)microglia subtype associated with increased immunoglobulinG4(IgG4) in the transverse colon (TC).

METHODS: We used immunohistochemistry (IHC), IgG4 repertoire profiling, and brain organoid experiments to explore this association.

RESULTS: CD83(+) microglia in the superior frontal gyrus (SFG) are associated with elevated IgG4 and human cytomegalovirus (HCMV) in the TC, anti-HCMV IgG4 in cerebrospinal fluid, and both HCMV and IgG4 in the SFG and vagal nerve. This association was replicated in an independent AD cohort. HCMV-infected cerebral organoids showed accelerated AD pathophysiological features (Aβ42 and pTau-212) and neuronal death.

DISCUSSION: Findings indicate complex, cross-tissue interactions between HCMV and the adaptive immune response associated with CD83(+)microglia in persons with AD. This may indicate an opportunity for antiviral therapy in persons with AD and biomarker evidence of HCMV, IgG4, or CD83(+)microglia.

The emergence of single nucleus RNA sequencing (snRNA-seq) offers to revolutionize the study of Alzheimer’s disease (AD). Integration with complementary multiomics data such as genetics, proteomics and clinical data provides powerful opportunities to link cell subpopulations and molecular networks with a broader disease-relevant context. We report snRNA-seq profiles from superior frontal gyrus samples from 101 well characterized subjects from the Banner Brain and Body Donation Program in combination with whole genome sequences. We report findings that link common AD risk variants with CR1 expression in oligodendrocytes as well as alterations in hematological parameters. We observed an AD-associated CD83(+) microglial subtype with unique molecular networks and which is associated with immunoglobulin IgG4 production in the transverse colon. Our major observations were replicated in two additional, independent snRNA-seq data sets. These findings illustrate the power of multi-tissue molecular profiling to contextualize snRNA-seq brain transcriptomics and reveal disease biology.

Variants in APOE and PSEN1 (encoding apolipoprotein E and presenilin 1, respectively) alter the risk of Alzheimer’s disease. We previously reported a delay of cognitive impairment in a person with autosomal dominant Alzheimer’s disease caused by the PSEN1^E280A variant who also had two copies of the apolipoprotein E3 Christchurch variant (APOE3^Ch). Heterozygosity for the APOE3^Ch variant may influence the age at which the onset of cognitive impairment occurs. We assessed this hypothesis in a population in which the PSEN1^E280A variant is prevalent.