IFN-γ identified as a powerful blood biomarker for Alzheimer’s

By Dr. Priyom Bose, Ph.D.Reviewed by Lauren HardakerFeb 19 2026

A new study uncovers interferon gamma as both a powerful blood-based signal of Alzheimer’s disease (AD) and a potential mechanistic bridge between genetic risk and damaging microglial inflammation in the brain.

Study: Identification of plasma inflammatory biomarkers for Alzheimer’s disease reveals IFN-γ as a regulator of ACSL1-mediated microglia phenotype. Image credit: Antonio Marca/Shutterstock.com

A recent study in Frontiers in Immunology investigated the diagnostic value of plasma inflammatory biomarkers for AD and examined the relationships between key biomarkers, cognitive performance, and APOE genotypes.

Barriers to Timely Diagnosis of Alzheimer’s Disease

Alzheimer’s disease (AD) is a progressive brain disorder that gradually impairs memory, thinking, and behavior. As populations age, the prevalence of AD has increased, making it the most common form of dementia worldwide. In rapidly aging societies like China, the incidence of AD and related dementias has surged, placing immense pressure on healthcare systems and families. The financial and social burden continues to grow as the disease becomes a leading cause of death and disability.

Although early diagnosis of AD is crucial for effective care, current diagnostic methods often fall short. Physicians usually diagnose AD using cognitive tests and advanced imaging. However, these approaches can be expensive, inaccessible, or subjective, particularly in less-resourced communities. Although tests for biomarkers in cerebrospinal fluid and blood, such as amyloid-β and phosphorylated Tau, are promising, they remain largely restricted to research settings due to their complexity and cost. This highlights the urgency of identifying simple, reliable, and accessible biomarkers for AD diagnosis.

Role of APOE ϵ4 in Microglial-Mediated Neuroinflammation in Alzheimer’s Disease

Microglia, the resident immune cells of the central nervous system, play a significant role in the pathogenesis of AD. These cells are activated by amyloid-beta plaques and neurofibrillary tangles, thereby initiating innate immune responses. While transient microglial activation may facilitate the clearance of pathological aggregates, sustained activation leads to the production of neurotoxic mediators and pro-inflammatory cytokines, thereby exacerbating neurodegeneration. Although differential expression of blood-based inflammatory biomarkers has been observed between AD patients and controls, the diagnostic specificity and utility of these markers remain incompletely understood.

The apolipoprotein E (APOE) ϵ4 allele is the most significant genetic risk factor for late-onset AD. Individuals carrying one or two copies of the APOE ϵ4 allele exhibit a markedly increased risk of developing AD. Beyond its established role in lipid metabolism, ApoE4 has been demonstrated to modulate microglial function, promoting neuroinflammatory cascades that exacerbate disease progression.

Recent studies have implicated ApoE4 in the induction of a pathogenic microglial phenotype characterized by lipid droplet accumulation, which contributes to neuronal injury and tau pathology. However, the precise molecular mechanisms underlying ApoE4-mediated microglial reprogramming and neuroinflammation in AD remain incompletely defined.

Assessing Inflammatory Biomarkers and Genetic Risk in Alzheimer’s Disease Detection

This study investigated the potential of blood-based inflammatory markers in aiding the diagnosis of AD and explaining their relationships with genetic risk factors and cognitive decline. Using a combination of blood markers, clinical information, and APOE genotype, a predictive model for AD was developed.

A total of 141 participants were enrolled in this study. AD diagnosis was based on clinical, neuropsychological, and imaging assessments according to established criteria. Researchers measured cognitive function with the Mini-Mental State Examination (MMSE) and Montreal Cognitive Assessment (MoCA), covering key cognitive domains.

MRI was conducted on a 3.0-T scanner to rule out unrelated intracranial abnormalities. Medial temporal atrophy (MTA) was independently assessed and discrepancies resolved by consensus, using age-adjusted criteria for abnormality.

Peripheral blood samples were collected and analyzed. APOE genotyping and analysis of inflammatory proteins were performed. Plasma inflammatory biomarkers were measured using Luminex multiplex technology.

IFN-γ and APOE4 Are Associated With, and May Jointly Promote Inflammatory Microglial Changes in AD

The study cohort included 71 people with AD, 44 with mild cognitive impairment (MCI), and 28 healthy controls (HC). AD patients were older, had less formal education, and were more likely to carry the APOE ϵ4 genotype. The sex distribution was similar across groups. Cognitive scores based on MMSE and MoCA were significantly lower in AD patients, reflecting reduced global cognitive function.

A total of 16 plasma inflammatory biomarkers were measured. Of these, IFN-γ, IL-33, and IL-18 were elevated, while IL-7, IL-6, and CCL11 were decreased in AD patients. Higher levels of IFN-γ, IL-33, and IL-18 were strongly associated with worse cognitive scores, whereas higher levels of IL-7, IL-8, and TSLP were associated with better scores. These results highlight substantial systemic inflammatory changes in AD.

Predictive models for AD were developed using LASSO regression with nested cross-validation. A model combining clinical variables, APOE genotype, and plasma biomarkers achieved the highest accuracy (cross-validated AUC = 0.953; full-cohort model AUC = 0.979), with IFN-γ contributing most to predictions. Importantly, IFN-γ alone distinguished AD from healthy controls (AUC = 0.913) and from MCI (AUC = 0.789), making it the strongest individual protein marker in the panel.

Plasma IFN-γ was highest in AD patients carrying the APOE ϵ4 allele. Transcriptomic analyses of publicly available human postmortem brain datasets revealed that inflammatory and IFN-γ-related pathways were most active in microglia from APOE4/4 AD patients. Subtypes of microglia were identified, with lipid droplet-accumulating microglia (LDAM) being especially expanded and showing high IFN-γ pathway activity in APOE4/4 AD.

Experimental findings confirmed that APOE4 increases ACSL1 expression, a marker of LDAM, in microglia. IFN-γ further boosted ACSL1 expression, particularly in APOE4-overexpressing cells. This in vitro evidence suggests that IFN-γ and APOE4 may interact to promote harmful microglial changes linked to AD pathology, although the study does not directly demonstrate that peripheral IFN-γ crosses the blood–brain barrier or causally drives microglial activation in vivo.

Conclusions

The current study demonstrates that IFN-γ is a promising and highly informative biomarker for AD, especially in individuals carrying the APOE ϵ4 allele. Elevated IFN-γ levels are closely linked to systemic inflammation and are associated with transcriptional signatures of brain-specific inflammatory pathways, promoting the expansion of harmful microglial subtypes through increased ACSL1 expression.

This mechanistic insight highlights the interplay between genetic risk factors and immune signaling in AD, providing a foundation for improved diagnostic strategies and targeted therapies to slow or prevent disease progression. However, the findings are based on a single-center, cross-sectional cohort and require independent validation, and direct in vivo evidence linking peripheral IFN-γ to central microglial activation remains to be established.

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