Blood-brain barrier model architecture shapes peripheral immune cell trafficking in Parkinson’s disease

Parkinson’s disease (PD) is a neurodegenerative disorder traditionally characterized by dopaminergic neuron loss in the substantia nigra pars compacta , but peripheral immune dysregulation and blood-brain barrier (BBB) dysfunction have been increasingly implicated in disease pathophysiology. However, how circulating immune cells interact with the human BBB and how these interactions are captured across experimental models remains poorly understood. In particular, human BBB models offer multiple platforms to interrogate these biological questions, with organ-on-chip approaches attracting significant interest. In this context, it is essential to determine whether model architecture influences the assessment of immune-endothelial interactions in PD, and if it may lead to fundamentally different interpretations of immune cell trafficking at the human BBB. Here, we compared peripheral blood mononuclear cells (PBMCs) from control donors or individuals with PD in human induced pluripotent stem cell (iPSC)-derived BBB models to determine how static and dynamic BBB systems influence immune cell behavior. To do so, we leveraged our brain chip platform to establish a model based on expression of the PD-associated SNCA triplication mutation. Using two-dimensional permeable membrane inserts and a three-dimensional (3D) microfluidic BBB chip, we evaluated PBMC attachment and transmigration according to PBMC disease status, endothelial cellular background (control or SNCA triplication), and exposure to α-synuclein (α-Syn) monomers or preformed fibrils (PFFs). PBMCs from PD donors showed increased baseline reactivity and altered endothelial interactions compared with controls. In insert-based models, greater PBMC attachment and selectively increased transmigration of PD PBMCs were associated with SNCA triplication vs. control endothelial cells, while PFF exposure increased attachment without affecting transmigration. In contrast, in the microfluidic BBB chip, attachment was largely unchanged by endothelial background or α-Syn exposure, whereas transmigration increased following α-Syn monomer pre-treatment. Together, PBMC-BBB interactions in PD appear to be shaped by immune cell status, endothelial background, and α-Syn exposure, but are strongly influenced by the architecture of the BBB model. This study underscores the importance of physiologically relevant multicellular and flow-based BBB systems and provides a human-focused framework for studying peripheral immune cell trafficking across the diseased BBB. These findings also emphasize that biological insights into BBB function are inherently shaped by the experimental model used, underscoring the need for complementary human BBB platforms.