Volunteers
Peripheral venous blood was collected from 88 volunteers enrolled in this observational cross-sectional study classified according to a previous COVID-19 diagnosis determined by PCR test for SARS-CoV-2 or household contact persons to PCR-tested persons which were not tested despite exposure from a previously published cohort of the first pandemic wave in spring 2020 by Wuhan type SARS-CoV-2 (Sonnleitner, Prelog et al. 2021). Blood samples were obtained between July 2020 and December 2020 6 to 9 months post infection or contacts in the area of East Tyrol, Austria, and the city area of Wuerzburg, Bavaria, Germany. Eight were PCR negative (PCR-), 51 were PCR positive (PCR+), and 29 were not PCR-tested (NT) who had household contact with SARS-CoV-2 infected PCR+ persons (Table 1). Symptomatic persons reported at least one symptom of the infection including headache, cough, temperature >38.5°C, fatigue or anosmia. All participants gave their written informed consent according to the principles of the declaration of Helsinski 2013 and ethical approval of the committee at the University of Wuerzburg (Protocol number 20201105_01).
Peripheral mononuclear blood cells (PBMCs) were isolated by density centrifugation (FicoLite-H, Linaris, Wertheim, Germany) according to standardized laboratory procedures and preserved in liquid nitrogen, while serum samples were preserved at -20°C until use.