IHC
As described by the source labs, specimens containing normal tissue were collected and sampled from anonymized paraffin embedded material of surgical specimens, in accordance with approval from the local ethics committee. The specimens were derived from surgically removed tissue, normal was defined by tissue specific morphological parameters and absence of neoplasia. IHC staining was performed on normal tissue microarray using a standard protocol (https://www.proteinatlas.org/download/IHC_protocol.pdf). Antibodies against human ACE2 (HPA000288, CAB026174), TMPRSS2 (HPA035787), CTSL (CAB000459), and FURIN (CAB009499) were labeled with DAB (3, 3’-diaminobenzidine) stain. Protein expression score was calculated for each receptor based on the staining intensity (negative, weak, moderate or strong) and fraction of stained cells (<25%, 25-75% or >75%). For each protein, the IHC staining profile was matched with mRNA expression data and gene/protein characterization data to yield an ‘annotated protein expression’ profile.