We next examined immunovascular interactions in PBMCs isolated from patients with COVID-19 and found increased adhesion of PBMCs to human brain endothelial cells in the cohort with long COVID compared to unaffected individuals, which was heightened in the presence of TNF and only modestly affected by blocking antibodies against ICAM-1 and VCAM-1 (Extended Data Fig. 8a,b). Here, TNF is linked to COVID-19.