IDO2 and long COVID-19: From our previous study6 we knew that in fatal COVID-19 various blood cells express IDO2 and thus we analyzed cytospins from purified PBMC, containing monocytes and lymphocytes from non-hospitalized PASC patients (n = 9) and fully recovered SARS-CoV-2-infected patients (n = 14; overview in Table 2) from the MUSCLE-PASC study.