The neurovascular unit (NVU) is critical for brain homeostasis through its roles in maintenance of an effective blood brain barrier (BBB) and regulation of cerebral blood flow. Perturbation of the NVU is a hallmark of the pathology of multiple neurodegenerative diseases resulting in loss of BBB integrity, neuroinflammation and neuronal dysfunction. The NVU is a complex structure composed of endothelial cells, pericytes, as well as central nervous system (CNS) glial and neuronal components. While the importance of the CNS vasculature in health and disease is well established, the mechanisms underlying vascular pathology and its contributions to neurodegenerative diseases are less well defined. Neuroinflammation and reactive gliosis occurs in the majority of neurodegenerative diseases and recent studies suggest that immune mediated disruption of the BBB contributes to the induction of reactive gliosis and neuronal dysfunction. Potential consequences of NVU disruption include immune-driven vascular inflammation and leukocyte infiltration in Multiple Sclerosis (MS), protease-mediated tight junction degradation in ischemic stroke (IS), α-synuclein–associated endothelial dysfunction in Parkinson’s Disease (PD), amyloid-β– and tau-induced pericyte injury in Alzheimer’s Disease (AD), and complement-mediated vascular damage in Amyotrophic Lateral Sclerosis (ALS). Here we review the nature of NVU perturbations in these common neurodegenerative diseases, with an emphasis on the contribution of immune modulation of BBB disruption in neuropathology and disease progression.

Diseases of the mature central nervous system (CNS), including Parkinson’s disease (PD), Alzheimer’s disease (AD), Multiple Sclerosis (MS), Ischemic Stroke (IS), and Amyotrophic Lateral Sclerosis (ALS), have distinct characteristics including the populations of cells affected, the molecular basis of the pathology, and the location of the disease. While distinct diseases, they share some common characteristics that include the activation of an immunological response and the perturbation of the functions of the neurovascular unit (NVU).

The NVU is a complex, dynamic structure composed of multiple different cell types (Figure 1). While the NVU was originally thought to simply be the basis of the blood brain barrier (BBB), recent studies indicate it is a far more dynamic element of the CNS (Badaut et al., 2024). The BBB acts as a selective barrier to prevent the unrestrictive passage of peripheral immune cells, pathogens and large molecular moieties from blood to the parenchyma of the brain (Friedman et al., 2025). The BBB is not a passive barrier but facilitates the active transport of selective substances between the lumen of the vasculature and the parenchyma of the brain (Erickson and Banks, 2018). Classical studies using dye tracing at the ultrastructural level (Reese and Karnovsky, 1967) demonstrated that the physical location of the barrier was at the interface between the endothelial cells lining vessels of the brain. These cells, commonly referred to as Brain Endothelial Cells (BECs), have been the subject of extensive investigation, and much is known regarding their molecular composition and response to injury (Yuan et al., 2023). Mature BECs are interconnected by two types of junctions: adherens junctions that provide structural support and maintain the close apposition of cells, and tight junctions, which are formed through interactions among membrane-associated proteins, including cytoplasmic zonula occludin proteins (e.g., ZO-1), transmembrane claudins (most notably claudin-5), and tight-junction–associated MARVEL proteins (TAMPs) such as occludin and tricellulin (Hudson and Campbell, 2021; Raleigh et al., 2010). Tight junctions fuse the plasma membranes of adjacent cells and are the critical element in the generation of the barrier. Considerable evidence suggests that BECs both respond to neuropathological triggers and influence the progression of the disease through the release of a variety of signaling molecules and cytokines (Sá-Pereira et al., 2012; Krueger and Bechmann, 2010; Bhattacharya et al., 2020).

Schematic of a healthy NVU consisting of astrocytes, oligodendrocytes, microglia, pericytes, and brain endothelial cells (BECs). The blood–brain barrier (BBB) comprises BECs held together by tight junctions and claudins. Pericytes and the basement membrane support the BBB and limits the flow of chemicals from the blood into the brain. Astrocyte endfeet wrap blood vessels to help reinforce the integrity of the NVU while simultaneously supporting neuron signaling and oligodendrocyte metabolism. Resting microglia serve as resident macrophages of the CNS helping to clear out debris. Red blood cells (RBCs) and immune cells, including leukocytes and B-cells, circulate in the blood. This figure was generated using BioRender.

The formation of the BBB by BECs is regulated by interactions with other cells within the NVU, including pericytes and astrocytes. Pericytes extend processes along blood vessels and are located between the endothelial cells and astrocyte endfeet (Sá-Pereira et al., 2012; Krueger and Bechmann, 2010; Bhattacharya et al., 2020). Based on cytoskeletal features and their exact positioning along the vascular tree, pericytes can be categorized into ensheathing pericytes (arteriole–capillary junction), mesh pericytes (pre- and post-capillary venules), and thin-strand pericytes (mid-capillary segments; Brown, 2019). Although these classes have been morphologically identified, brain pericytes do not appear to exhibit distinct subtypes at the transcriptomic level and collectively appear to be critical for the formation and maintenance of the BBB (Blanchette and Daneman, 2015; Dalkara et al., 2011; Vanlandewijck, 2018). One of the major signaling pathways between BECs and pericytes is through the PDGFb/PDGFbR pathway, and inhibition of this pathway results in failure of CNS vessel formation and stabilization (Daneman, 2010; Armulik et al., 2010; Betsholtz and Keller, 2014). Other signaling pathways such as Notch and TGF-β have also been shown to be important in the adhesion, proliferation, and migration of pericytes (Krueger and Bechmann, 2010), and their perturbation results in a breakdown of the BBB, hemorrhaging, and perivascular edema (Bhattacharya et al., 2020; Allinson et al., 2012; Gaengel, 2009). Given their critical role in the maintenance of the NVU function, it is not surprising that pericytes have been implicated in a variety of neuropathological conditions.

Another crucial cellular element of the NVU is astrocytes (Liu et al., 2020; Aharoni et al., 2021; McConnell and Mishra, 2022). Astrocytes, which are the most abundant glial cell type in the CNS, are a major class of spatially and functionally heterogeneous glial cells (Bocchi et al., 2025; Serrano-Pozo et al., 2024; Miedema, 2024; Schitine et al., 2015; Bacchi, 2025; Qian et al., 2023) that support neuronal metabolism, regulate synaptic function and myelination, and respond to CNS injury (Alberini, 2018; Babenko et al., 2024; Barres, 2008; Ishibashi et al., 2006; Sofroniew and Vinters, 2009; Stogsdill et al., 2023). Astrocyte processes cover the surface of most CNS vessels and are thought to play multiple roles, including formation and maintenance of the BBB. For example, under specific conditions, astrocytes release pro-inflammatory and anti-inflammatory cytokines that modulate BBB permeability (Manu et al., 2023; Michinaga and Koyama, 2019), while the retraction of astrocyte endfeet around CNS capillaries during inflammation increases BBB vulnerability and, potentially, CNS damage (Manu et al., 2023; Ponath et al., 2018; Salles, 2022).

In pathogenic states, perturbation of the NVU may result in hypoxia, increased inflammatory activity (Stanimirovic and Friedman, 2012), and a secondary cascade of events resulting in the disruption of the BBB (Balasa, 2021), in turn allowing the trafficking of proteins such as fibrin into the CNS. In diseases such as multiple sclerosis, active lesions are characterized by increased leukocyte infiltration (Sweeney et al., 2019) and lesions develop around small, inflamed veins (Gaitán et al., 2011), suggesting that damage to the NVU contributes to the development of neuroinflammatory diseases in the CNS. It is becoming increasingly evident that the pathology of many neurological diseases, regardless of the initial insult, reflects engagement of the immune system and NVU dysfunction. In this review, we integrate emerging evidence that immune–NVU interactions, particularly those involving B cells and glial populations, play a central role in BBB engagement across multiple neurodegenerative diseases, offering a unifying framework for disease progression that extends beyond disease-specific models.

Multiple sclerosis (MS) is a chronic autoimmune, neuroinflammatory, demyelinating disease of the CNS. MS is characterized by localized myelin damage and axonal injury, with lesions predominantly located in brain and spinal cord. CNS white matter is comprised of myelinated and unmyelinated axons, astrocytes, oligodendrocytes, and vascular elements, with the high lipid content of myelin contributing to its opaque white appearance (Walhovd et al., 2014). Symptom onset in MS typically presents in young adults, with a higher prevalence in women than men (Liu et al., 2022), and includes motor dysfunction, tremors, fatigue, nystagmus, paralysis, ataxia, and vision impairment (Ortiz, 2014).

MS is a heterogeneous disease classified into relapsing–remitting MS (RRMS), secondary-progressive MS (SPMS), primary-progressive MS (PPMS), and progressive-relapsing MS (PRMS), with the most common type being RRMS, impacting people in early adulthood (Liu et al., 2022). In RRMS, patients experience relapses that temporarily dampen specific neurological functions, followed by a period of remission in which some functionality is regained. In some patients, the disease transitions to a more progressive SPMS condition (Cree and Hartung, 2025). The rate of progression is variable; some patients never transition to SPMS, while those who do, develop a steadily progressing form of the disease. By contrast, PPMS is characterized by continuous disease progression from onset. In comparison, PRMS is characterized by a constant disease progression that is accompanied by acute relapses with no remission (Dutta and Trapp, 2014).

The ambiguous nature of MS pathology makes reaching a definitive diagnosis difficult in earlier stages of the disease. Initial diagnoses based on changes in inflammation across different regions of the CNS was later amended to include measurements of oligoclonal immunoglobulin G (IgG) bands (OCB) in the patient’s cerebrospinal fluid (CSF; McDonald, 2001; Thompson et al., 2018; Deisenhammer et al., 2019). The increase in IgG levels, coupled with disease progression, likely reflects the differentiation of B cells into plasma cells in response to signals received from T helper cells (Th17; Vaillant, 2023; Graner et al., 2020).

Lesion formation and local demyelination are associated with local inflammatory responses associated with infiltrating autoreactive immune cells (Cui et al., 2020; Cashion et al., 2023). At the level of the NVU, early signs of MS involve cytokine cascades triggered by T-cells, leading to the destruction of cerebral blood vessel integrity enabling the admission of inflammatory leukocytes into the CNS (Ortiz, 2014). One hypothesis is that a breakdown of tolerance established during the gestational and postnatal periods stimulates regulatory T cells (Tregs) to exhibit a pro-inflammatory state and secrete proinflammatory proteins (Cui et al., 2020; Tanaka et al., 2014). Consequently, cells such as peripherally activated microglia, activated B cells, and Th17 cells, are recruited into the CNS, resulting in either protective or pathogenic responses (Cashion et al., 2023; Tanaka et al., 2014). While the role of major classes of CNS cells in MS pathology has become more defined, the role of the NVU is often overlooked (Figure 2).

Representation of immunological involvement and dysfunction of the NVU in multiple sclerosis (MS). The loss of claudins and tight junctions, followed by astrocytic endfeet retraction, results in the disruption of the BBB. Immune cell transmigration is facilitated by an increase in the expression of VCAM-1 and ICAM on endothelial cells. Fibrinogen leakage into the brain initiates coagulation, while fibrin deposition promotes OPC clustering, which activates BMP signaling and inhibits oligodendrocyte differentiation. This blockade of differentiation drives OPCs to target astrocytic endfeet, preventing vascular ensheathment and contributing to their retraction. Local inflammation is a result of the weakened BBB, allowing the infiltration of macrophages, activated microglia (microgliosis), and plasma B cells in peripheral blood, T-regulatory cells (Treg) send activation signals, prompting T-helper cells to secrete IL-17, IL-21, and IL-22 as they shift into a pro-inflammatory state. This stimulates peripheral B-cells to shift to antibody-producing plasma B cells through the expression of major-histocompatibility complex II (MHC-II). The release of IL-6, MMP9, TNF-a, and CCC-2 from pericytes further amplifies neuroinflammation and the disruption of the BBB. This figure was generated using BioRender.

In MS, lesions typically form around blood vessels (Gaitán et al., 2011), where local demyelination of axons compromises their conduction potential, resulting in neurological deficits (Lassmann, 2003). Neurovascular cells, including BECs, pericytes, astrocytes, and microglia, are impacted during the development of MS pathology and may contribute to a pro-inflammatory state of the CNS (Daigle et al., 2025; Iadecola, 2017; Schreiner et al., 2022). Linkage between adjacent BECs weakens during inflammation as tight junctions are lost, allowing increased leukocyte trafficking into the CNS (Cayrol, 2008). Key molecules involved include VCAM-1, ICAM-1, IL-4, IL-10, TNFα, and IFN-γ (Cayrol, 2008; Raine, 1995; Cashion et al., 2023). Inflammatory cues also drive mislocalization of chemokines like CXCL12 and upregulation of leukocyte adhesion molecules on BEC surfaces, including VCAM-1 (Allavena et al., 2010), DARC (Minten et al., 2014), and ALCAM (Cashion et al., 2023; Cayrol, 2008). Notably, ALCAM knockout mice develop more severe experimental autoimmune encephalomyelitis (EAE), a widely used animal model for MS (Constantinescu et al., 2011), suggesting a compensatory role in maintaining BBB integrity (Lécuyer et al., 2017). These changes likely reflect BEC responses to inflammatory signals from surrounding cells, such as pericyte-mediated induction of adhesion molecules (Bisht et al., 2021).

During inflammatory episodes in the CNS, pericytes appear to induce constriction of cerebral blood vessels for extended periods (Fortune, 2025). Studies in animal and human tissue identified PDGFRb, CD13, α-smooth muscle actin (αSMA), NG2, and Atp13a5 as pericyte-specific markers (Kang, 2020; Guo et al., 2024), and in disease, an increase particularly in aSMA and NG2 expression usually indicates pericyte activation (Ferrara et al., 2016; Verbeek et al., 1994). It is important to note that while markers like PDGFRβ and NG2 are widely used, their specificity remains an active area of research. Markers such as αSMA are also expressed by vascular smooth muscle cells, and others, including PDGFRβ, are found on CNS fibroblasts and other mesenchymal cells, particularly near the meninges or in areas of injury (Yao, 2022). This cellular heterogeneity and marker overlap makes precise identification of the pericyte population challenging in pathological settings. In addition to reducing blood flow, pericytes facilitate the migration of immune cells into the CNS via the antigen-presenting molecule, MHC-II, promoting the recruitment of activated T-cells (Silva et al., 2021). Inflammatory T-cells appear to depend on MHC-II-presenting pericytes to proliferate as pericyte removal results in a decrease in the inflammatory T-cell population within the CNS (Silva et al., 2021), supporting the idea that pericyte dysfunction plays a role in MS and permits the transit of inflammatory cells across the BBB. For example, the loss of pericytes is associated with a reduction in tight junctions, decreased claudin-5 expression, and enhanced infiltration of blood-derived proteins into the CNS (Aharoni et al., 2021; Monsour and Borlongan, 2023), while activated pericytes may promote leucocyte adhesion (Choe, 2022) and secrete pro-inflammatory cytokines including TNF-α, IL-6, matrix metalloproteinase 9 (MMP9), and the chemokine CCL-2 (Bhattacharya et al., 2020; Cashion et al., 2023; Meyer-Arndt et al., 2023). The functions of MMP9 in the setting of neuroinflammation are complex, and it has been suggested that MMP9 may disrupt the vascular basement membrane, although it may also be that MMP9 overexpression results in pericyte loss and BBB hyperpermeability through compromising tight junctions (Dohgu et al., 2019).

Astrocytes are a central element in the pathology of MS. The retraction of their endfeet contributes to the weakening of the integrity of CNS vasculature and initiates their secretion of neuroinflammatory factors signaling for oligodendrocyte precursor cells (OPCs) to cluster around cerebral capillaries instead of axons (Cashion et al., 2023; Ortiz and Eroglu, 2024). Within MS lesions, astrocytes become reactive and reduce their coverage of the vasculature, resulting in perturbation of the basal lamina and disruption of the NVU (Figure 3). Additionally, astrocytes have been proposed to play a role in neurovascular coupling (NVC) and the regulation of neural activity in response to cerebral blood flow, which is diminished in MS (Stickland et al., 2019; Lia, 2023). Likewise, interactions between the NVU and ECM regulating trafficking between the CNS and blood may modulate synaptic plasticity (De Luca, 2020). The role of astrocytes in MS has been extensively reviewed, revealing robust morphological and transcriptomic changes that both contribute and respond to disease (Salles, 2022; Ortiz and Eroglu, 2024) (Figure 4).

The NVU is altered in EAE, a mouse model of MS. Electron microscopy images of the NVU in (A) naïve control or (B) EAE mice. Endothelial cell lining the blood vessel is represented by the white dashed line. Yellow or red asterisks represent healthy or missing astrocyte endfeet, respectively. BV – blood vessel. Scale bars 5uM.

Astrocyte and microglial density increase with EAE disease severity. Representative IHC showing GFAP+ astrocytes and IBA1 + microglia/macrophages in spinal cords from naïve mice and EAE mice with clinical scores of 2 and 4. Scale bars 50uM.

Microglia, while not an integral part of the NVU, influence NVU integrity in a number of ways during inflammatory episodes. For example, microglia can exist in multiple states that may be either anti-inflammatory (M1) or proinflammatory (M2; Ding et al., 2021; Mirarchi et al., 2024), with the pro-inflammatory state dominating in areas of MS lesions (Figures 4, 5). Proinflammatory microglia secrete a range of cytokines including TNF-α, nitric oxide (NO) and matrix metalloproteinase (MMPs), and may modulate neurovascular ECM (Lloyd et al., 2019) and the expression of tight junction proteins in BECs (Smith, 2022; Smith, 2022). Due to a high level of motility, microglia quickly migrate to damaged vessels and extend their processes to regions vacated by astrocyte endfeet (Bisht et al., 2021), a response that is muted in the setting of widespread neuroinflammation (Smith, 2022) possibly because of reduced recruitment to blood vessels via decreased ATP release through PANX1-P2RY12 receptor coupling (Bisht et al., 2021). The most upregulated pathways in EAE microglia include Wnt signaling, ECM and synaptic transmission pathways, indicating the multifaceted roles of microglia during disease (Ahn, 2023).

While the majority of studies in MS and animal models such as EAE have focused on the pathology and disruption of the NVU in the spinal cord, in part because lesion burden is high and clinical motor dysfunction can be readily quantified, it is clear that MS pathology in humans also involves substantial inflammatory and neurodegenerative changes in the cortex, deep gray matter, and optic nerve. The cell and molecular mechanisms underlying lesion development in these regions are less well understood, although recent studies using EAE models and cranial window based analyses (Yousefi, 2025) suggest that cortical NVU breakdown in EAE is associated with early pericyte injury, BBB dysregulation, and neuroinflammation. These observations support the hypothesis that widespread effects on the NVU of the cortex contribute to neuroinflammation and neurodegeneration and emphasize the need to integrate a global understanding of NVU biology to obtain a complete picture of disease mechanisms.

A characteristic of MS is the influx of T and B cells into the CNS resulting in BBB breakdown and subsequent neuronal degeneration (Silva et al., 2021; Brummer et al., 2022). In MS, B cells have been detected in white matter, meninges, and CSF (Lucchinetti, 2000) and have been shown to have a higher pro-inflammatory profile compared to those in healthy individuals (Seals, 2022; Li et al., 2018). The success of B cell-targeted therapies like rituximab, ofatumumab, and ocrelizumab in treating different stages of the disease, preventing new lesion formation, and reducing relapse rates highlights the crucial role of B cells in disease progression (Hauser et al., 2008; Hauser et al., 2017; Montalban, 2017). While the target of B cell generated autoantibodies and inflammatory cytokines is generally considered to be neurons and glia, B cells also play an important role in modulating the NVU through their interactions with BECs. Within MS lesions, BECs upregulate adhesion molecules VCAM-1 and ICAM-1 at B cell infiltration sites, which correlate with the expression of B cell counter-receptors VLA-4 and LFA-1 and facilitate B cell migration into the CNS. Several studies have explored the therapeutic potential of targeting VLA-4 in B cells (Rodriguez-Mogeda et al., 2022) that suggest a reduction in B cell migration across BECs by disrupting VLA-4’s interaction with fibrinogen (Cannella and Raine, 1995).

In B-cell-dependent EAE models, VLA-4 deletion in B cells leads to decreased recruitment of proinflammatory B cells, Th17 cells, and macrophages into the CNS, resulting in a significant reduction of clinical symptoms that was independent of peripheral B and T cells (Zamvil, 2015). These results suggest that the effects are primarily due to the selective inhibition of B cell recruitment into the CNS. Conversely, in B-cell-independent EAE models, VLA-4 deficiency in B cells resulted in more severe EAE. This was linked to a significant reduction in regulatory B cells (Bregs) within the CNS, highlighting the importance of VLA-4 for Breg migration and their neuroprotective role (Lehmann-Horn et al., 2016). Additionally, recent clinical studies with natalizumab, a VLA-4 blocking therapy, have shown reduced but not completely blocked immune cell infiltration into the CNS (Kowarik et al., 2021). These findings suggest that the role of VLA-4 on B cells can be either proinflammatory or neuroprotective, depending on the context of the EAE model and the activation state of the B cells. For example, the differential effects of VLA-4 may reflect a subset-specific reliance on VLA-4–mediated trafficking, with regulatory B cells being particularly dependent on VLA-4 for CNS entry during neuroinflammation. We hypothesize that context-dependent differences in B-cell activation state and integrin usage help explain the opposing effects of VLA-4 loss observed in B-cell-dependent versus B-cell-independent EAE models.

In addition to their interactions with BECs, B cells also play a crucial role in modulating the NVU through their effects on glial cells. The presence of proinflammatory B cells alongside reactive glial cells suggests that B cells may significantly influence local gliosis. Astrocytes and microglia may exist in different anti- and pro-inflammatory states that can be influenced by B cells. For example, astrocytes cultured with EAE B cells but not controls resulted in morphological changes (Ahn, 2023) and could induce damage to oligodendrocytes. Transcriptional analysis of EAE astrocytes following B cell depletion suggested that B cell depletion did not reverse astrocytic neuroinflammatory pathways; instead, the top differentially expressed pathways were associated with interaction via NVC and focal adhesion kinase (FAK) pathways, suggesting that functional recovery following B cell depletion is driven by enhancements to the NVU rather than by the direct suppression of inflammation. These findings were further validated in situ, with consistent Cldn 5 expression around blood vessels, a significant reduction of albumin leakage, and decreased immune cell filtration into the spinal cord parenchyma in B cell depleted animals compared to controls (Ahn, 2023).

The role of B cells in MS is clearly complex. In a longitudinal study analyzing published single-cell sequencing data from Maggi (2023) found that B cell depletion was effective in suppressing activated microglia and preventing them from escalating their immune response. Specifically, depletion of CD20 B cells was predicted to affect microglial genes involved in iron/heme metabolism, hypoxia and antigen presentation. However, in vivo validation via MRI data demonstrated B cell depletion did not significantly reduce white matter lesion volume or mitigate the chronic inflammatory process over longer periods, particularly in paramagnetic rim lesions (PRLs). Additionally, in chronic active lesions (CALs), CD20 B-cells comprised a small percentage of all lymphocytes and were outnumbered by plasmablasts and activated T-cells. These findings suggest that while peripheral B-cell depletion is effective in preventing new lesion formation, it does not sufficiently resolve the activity of iron-laden microglia at the edge of chronic active lesions that are isolated behind a closed BBB in prolonged periods of disease (Maggi, 2023).

Reactive gliosis and immune cell infiltration in MS lesions. Immunohistochemistry shows morphological changes in astrocytes (GFAP+) and microglia/macrophages (Iba1+) within the lesion core (white matter, right of yellow line) compared to adjacent gray matter (left of yellow line) in an EAE mouse with clinical score 2. Scale bars 75uM.

The interactions between B cells and components of the NVU—including BECs, astrocytes, and microglia—underscore the multifaceted role of B cells in modulating BBB integrity, leukocyte infiltration, neuroinflammation, and gliosis in MS. Further studies are needed to illuminate the complexity of B cell function within the CNS and open avenues for targeted therapies aimed at preserving NVU function and mitigating disease progression in MS.

Significant progress in the treatment of MS has been made since the introduction of interferon beta-1b (IFNβ-1b) in 1993 (Paty and Li, 1993). Since then, therapies with increasing efficacy, selectivity, and safety have been developed, broadening our understanding of the disease and increasing the window for therapeutic intervention (Montalban, 2017; Kappos et al., 2020). Nevertheless, there is no cure for the disease and many of the current strategies focus on targeting the immune system to reduce inflammatory cytokines or prevent the entry of immune cells into the CNS, thereby reducing acute attacks. However, emerging therapeutics are beginning to target vascular-mediated functions to slow or halt the progression of disease.

MS has long been known to be a T-cell associated disease due to robust T-cell infiltration into the CNS, leading to cytokine release and impairment of tight junctions along the BBB (Wagner et al., 2019). However, early clinical trials with purely T-cell based approaches were found to be ineffective (van Oosten, 1997; Weinshenker, 1991). Later strategies were developed to inhibit lymphocyte infiltration into the CNS (Polman et al., 2006). Approved by the FDA in 2004, natalizumab is a selective adhesion-molecule inhibitor that prevents binding of α4β1 and α4β7 integrins to their receptors, thereby modulating inflammatory reactions in the CNS (Polman et al., 2006). Treatment with natalizumab in RRMS patients reduced the risk of sustained progression of disability by 42% and the rate of clinical relapse by 68%, further supporting the role of lymphocyte migration and vascular dysfunction in disease progression. Subsequent in vitro studies showed that very high levels of ICAM-1 would be required to allow natalizumab to thwart T-cells’ attack on BECs effectively (Soldati et al., 2023). Other disease-modifying therapies (DMTs) have since been approved for relapsing and progressive disease, including cladribine, ocrelizumab, ofatumumab, siponimod, and ponesimod (Montalban, 2017; Giovannoni et al., 2010; Kappos, 2018; Hauser, 2020; Kappos, 2021). The continuous development of DMTs with different mechanisms of action and varying rates of disease control highlight the complex role of the BBB and the need to evaluate disease activity to determine the best course of treatment.

Since the success of rituximab, a monoclonal antibody targeting CD20, a significant amount of evidence suggesting the involvement of B cells rather than T cells has accumulated (Chisari et al., 2022). B-cell directed therapies such as rituximab, ocrelizumab and ofatumumab have investigated targeting B-cells by antibody-mediated depletion (Hauser et al., 2008; Hauser et al., 2017; Hauser, 2020), showing greater functional improvement, lower relapse rates, and reduced rate of lesions. Interestingly, treatment of teriflunomide, an oral DMT that inhibits pyrimidine synthesis and reduces T cell and B cell activation, resulted in higher annualized relapse rates compared to ofatumumab (Hauser, 2020). While teriflunomide significantly reduces B cell counts in patients, T cells are affected to a lesser extent (Gandoglia et al., 2017). More recently, chimeric antigen receptor T cell (CAR-T) technology, initially used for the development of therapies for hematological malignancies, has shown promise as a potential treatment for MS. In 2024, a fully human autologous CD19 CAR-T cell therapy (KYV-101) was used to treat two patients with progressive and refractory MS, resulting in acceptable safety profiles and reduced intrathecal antibodies (Fischbach et al., 2024). One hypothesis for the shortcoming of current B-cell targeted therapies in effectively preventing relapses is that monoclonal antibodies such as rituximab and ocrelizumab do not adequately cross the BBB to influence CNS B cell function. Increased knowledge about the involvement of the CNS vasculature in MS pathogenesis provides rationale for the clinical evolution of MS therapies that target the BBB (Monson, 2005). KYV-101, on the other hand, was observed in the CSF and expanded without signs of immune effector cell-associated neurotoxicity syndrome (Fischbach et al., 2024). These B cell directed therapies not only demonstrate B cell involvement in disease progression but also suggest a role for B cells that have already accumulated in the CNS.

There are currently multiple potential therapies available to treat MS. The majority of these are focused on modulating the effects of the immune system, either through altering inflammatory cytokines or preventing the entry of immune cells into the CNS. While originally thought to be a predominantly T cell mediated disease, the development of B cell depleting therapies have identified a central role for B cells in mediating disease progression.

While not considered a classic neuroinflammatory disease, extensive data suggests there is a pivotal role for changes in the NVU in driving the ongoing pathogenesis in Ischemic Stroke (IS). IS is the leading cause of disability worldwide (Katan and Luft, 2018) and the majority of early studies focused on the loss of neuronal function, including mitochondrial dysfunction, excitotoxicity, and neuronal death (Dirnagl, 2012). It is thought that one of the leading causes of IS are plaques within cerebral vessels and infarcts from vessel lesions (Bailey et al., 2012), expanding the mechanisms of IS to include the NVU and its cellular components. Similar to the pathophysiology of multiple sclerosis, the involvement of the NVU in IS can both contribute to disease or repair of CNS tissue through processes involving glia, neurons, and matrix components of the NVU.

The deleterious effects of IS stem from several key pathophysiological factors involving the cerebral vasculature. During the acute phase of cerebral ischemia glutamatergic excitotoxicity, calcium overload, and oxidative stress are accompanied by BBB damage (Dohmen et al., 2005). Breakdown of the BBB results in increased permeability and downregulated expression of tight junction proteins such as claudin-5 (Stamatovic et al., 2019). Accompanied by the conversion of BBB endothelial cells toward a pro-inflammatory phenotype, an upregulation of adhesion molecules, ICAM-1 and VCAM-1, increases peripheral immune infiltration into the CNS (Supanc et al., 2011). The resulting leukocyte infiltration in the CNS and upregulation in inflammatory pathways triggers neuronal death and glial activation that may restrict recovery and repair of the tissue. Hence, it is critical to target repair of the NVU and BBB as treatment avenues for IS.

Glial cells of the NVU contribute to BBB breakdown by upregulation of proteolytic enzymes, including MMPs. MMP-9 is involved in degradation of the extracellular matrix and basal lamina, resulting in infiltration of peripheral immune cells (Ramos-Fernandez et al., 2011; Wang, 2018). While the exact role of MMP-9 in the development of IS has yet to be defined, it is clear there is a strong association of increased MMP-9 with severity of IS and worsened functional outcome (Ramos-Fernandez et al., 2011; Horstmann et al., 2003; Moldes, 2008; Montaner, 2001). Enhanced expression and activity of MMP-9 is localized around blood vessels, accompanied by increased neutrophil infiltration and macrophage activation (Rosell, 2006). Conversely, inhibition of MMP-9 activity has been shown to rescue fu