Taking a Glimpse Into the Brain's Immune System: Imaging and Blood-Based Biomarkers of the Poststroke Immune Response.

Stroke triggers a multifaceted and dynamic immune response, engaging both innate and adaptive mechanisms that evolve in distinct spatial patterns. While these processes contribute to tissue repair and debris clearance, they also drive secondary injury, shape long-term recovery, and predispose patients to life-threatening complications such as infections and recurrent vascular events. Importantly, preexisting systemic inflammation and immune alterations may interact with the poststroke immune cascade, amplifying risk for complicating outcomes. Despite recent advances, the translation of immunomodulatory therapies remains limited, highlighting the need for a better understanding of immune mechanisms in human stroke. Blood-based biomarkers, including cytokines, chemokines, alarmins, and immune cell profiles, have not only emerged as promising tools to monitor the poststroke immune response but also as potential therapeutic targets. At the same time, advanced neuroimaging techniques are opening new avenues to visualize blood-brain barrier breakdown, microglial activation, and other hallmarks of cerebral inflammation. Together, these circulating and imaging biomarkers offer complementary insights into the evolving brain-immune crosstalk after stroke. This review synthesizes current concepts of poststroke immune responses, systemic interactions, and the role of established and emerging blood-based and imaging biomarkers. We highlight the translational potential of integrative biomarker strategies to improve individualized prognosis, guide precision therapies, and ultimately bridge the gap between mechanistic discovery and clinical application.