METRNL and infection: Importantly, infection enhanced the expression of genes involved in the browning process, such as Ucp1, Pgc1a (coding for peroxisome proliferator-activated receptor gamma coactivator 1 alpha), Fgf21 (coding for fibroblast growth factor 21), Apln (coding for apelin), Metrnl (coding for meteorin-like protein), and Tmem26 (coding for transmembrane protein 26)42–45 in preadipocytes (MOI of 1, at 24, 48, and 72 hpi) (Fig. 6d).