TNF and COVID-19: In contrast, the immune effector function of PBMCs was related to COVID-19 severity, as mononuclear cells obtained from patients, who suffered from severe to critical disease, demonstrated higher levels of interleukin 10 (IL10, p = 0.044) and tumour necrosis factor (TNF, p = 0.024) mRNA expression as compared to subjects with a milder course of COVID-19 (Fig. 2).