Neurological symptoms are recognized in patients with COVID-19, and include anosmia, ageusia, cognitive impairments as well as more severe complications including encephalitis and ischemic strokes. Furthermore, persistent cognitive impairment including 'brain fog' is recognised as part of the long COVID syndrome. While SARS-CoV-2 has been shown to infect cells of the central nervous system (CNS) in vitro and in vivo, it is unclear whether direct infection of the CNS or indirect mechanisms including activation of the coagulation cascade or immune activation are the key drivers of COVID-19 neuropathology. We investigated whether inactivated SARS-CoV-2, or spike protein, can disrupt the integrity of the blood-brain barrier (BBB) and characterised neuroinflammation in the absence of infection. Using an in vitro model of the BBB composed of primary human microvascular endothelial cells, astrocytes, pericytes and microglia, we observed BBB disruption following exposure of the model to SARS-CoV-2 or spike protein. Importantly, loss of BBB integrity was observed in response to luminal (mimicking 'blood side') or abluminal ('brain side') exposure to inactivated virus or spike protein. Transcriptional upregulation of a range of chemokines, inflammatory cytokines and adhesion factors, and release of inflammatory cytokines from BBB models was also observed in response to luminal or abluminal SARS-CoV-2 or spike protein exposure. These data indicate that BBB disruption and immune activation in vitro occurs in response to SARS-CoV-2 in the absence of infection, highlighting the importance of the host immune system in BBB disruption during SARS-CoV-2 infection.
