For the precise determination of TMPRSS2 protein expression in HF specimens, we examined both skin-embedded HFs (Fig. 3, Supplemental Figure S1 B, D), which contain all skin appendages, such as sebaceous glands, sweat glands, smooth muscle cells, and adipocytes, and freshly plucked HFs (Fig. 3). Here, TMPRSS2 is linked to hydrops fetalis.