Challenge-based ex vivo immune profiling reveals stimulus-dependent peripheral immune reprogramming in Alzheimer's...

Altered immune function is increasingly recognized as a contributor to Alzheimer's disease (AD); however, it remains unclear whether peripheral immune alterations reflect constitutive inflammation or stimulus-dependent changes in immune responsiveness. Addressing this distinction is critical for understanding immune dysregulation in neurodegenerative diseases. In this study, we applied a challenge-based ex vivo immune profiling approach to characterize functional immune responsiveness in patients with AD and in cognitively healthy older adults. Peripheral blood mononuclear cells were exposed to defined innate, antigenic, and mitogenic stimuli, and cytokine and β-amyloid (Aβ) responses were quantified in culture supernatants. Diagnosis-by-stimulus interaction effects were assessed using generalized estimating equation models, adjusted for age and sex. In parallel, exploratory correlation-based immune-amyloid network analyses and hypothesis-driven immunogenetic stratification were performed to investigate biomarker coordination patterns and context-dependent genetic influence. Baseline cytokine concentrations showed limited between-group differences, whereas ex vivo immune challenge revealed selective stimulus-dependent alterations in cytokine production. In contrast, immune stimulation revealed selective amplification of stimulus-evoked responses in AD, particularly involving interferon gamma (IFN-γ), interleukin (IL)-4, and IL-10, whereas classical proinflammatory cytokines retained preserved inducibility. Exploratory genotype-stratified analyses suggested potential context-dependent differences in functional immune and Aβ responses to immune challenges. Together, these findings indicate that peripheral immune dysregulation in AD is characterized by stimulus-dependent differences in cytokine production that become apparent under immune challenge conditions, highlighting the value of ex vivo immune stimulation assays in translational immunology in neurodegenerative diseases.