Serum of Post-COVID-19 Syndrome Patients with or without ME/CFS Differentially Affects Endothelial Cell Function In Vitro.

Observed Findings

• Anti-endothelial cell autoantibodies (AECAs) were significantly more abundant in PCS/CFS patient serum compared to PCS and healthy controls.
• Both PCS and PCS/CFS sera reduced surface expression of several endothelial cell activation markers unexpectedly.
• PCS sera significantly promoted angiogenesis (new blood vessel formation) in vitro, while PCS/CFS sera did not show this enhancement.
• Both patient groups' sera induced release of molecules that inhibit nitric oxide-mediated endothelial relaxation, a key mechanism in blood vessel function.
• Cytokine profiles in serum showed only marginal differences between PCS, PCS/CFS, and healthy control groups.

Inferred Conclusions

• PCS sera may trigger compensatory pro-angiogenic mechanisms to counteract endothelial dysfunction, whereas PCS/CFS patients lack this adaptive response.
• AECA-mediated endothelial damage may represent a distinguishing pathophysiological mechanism in PCS/CFS compared to broader PCS.
• Both patient groups exhibit impaired nitric oxide-dependent endothelial relaxation, contributing to vascular dysfunction and potentially symptom generation.
• The differential functional effects between PCS and PCS/CFS suggest distinct immunopathological mechanisms despite both conditions following COVID-19.

Remaining Questions