HSD17B1 and viral infectious disease: Interestingly, the mRNA level of Hsd17b1 gene (a non-rate-limiting metabolic enzyme for both testosterone and estradiol biosynthesis) was markedly down-regulated following viral infection (Fig. S1c), which might account for the unchanged serum levels of testosterone and estradiol in SeV-infected mice (Figs. 1a and S1a).