Immune and Clotting Dysfunction Detected in Saliva and Blood Plasma after COVID-19.

It is becoming increasingly clear that individuals recovered from acute coronavirus disease 2019 (COVID-19) can develop into long-term sequelae (post-acute sequala of SARS-CoV-2 infection, PACS). While antibody response kinetics against viral particles is well studied in natural infection and vaccine, the molecular mechanisms governing disease formation remain elusive. We investigated plasma and saliva samples from COVID-19 and healthy control subjects to understand early immune responses globally after exposure to the virus. Antibody analyses showed robust IgA and IgG responses, neutralizing functions to the SARS-CoV-2, and positive correlations between matched plasma and saliva fluids. Shotgun proteomics revealed persistent inflammatory patterns in convalescent samples including dysfunction of neutrophil-fibrinogen axis, and dysregulated immune and clotting functions. Our study suggests saliva as fluid to monitor serology and immune functions to detect early and chronic signs of disease development. Further delineation of the pathophysiology in saliva may lead to discovery of novel biomarkers and therapeutic targets to patients at risk to develop PASC and chronic conditions. ### Competing Interest Statement The authors have declared no competing interest.