TLR3 and COVID-19: To test this, we performed ex vivo stimulation of PBMCs from healthy or COVID-19–infected individuals, using a mixture of synthetic TLR7 and TLR 8 (TLR7/8) and TLR3 ligands, which are known to be expressed by viruses, and we performed an intracellular staining assay to detect cytokine responses.