HPRT1 and pulmonary fibrosis: A previous study focusing on the initial inflammatory phase in the bleomycin-induced pulmonary fibrosis model found Hprt, Ppia and Sdha to be the most stable reference genes [13], and our results confirmed the very same genes, with the addition of Polr2a, as acting reliably as reference genes in RT-qPCR at a later stage in pulmonary fibrosis.