ABCB4 and Hepatic fibrosis: Hence, we hypothesized that vitamin D supplementation ameliorates liver fibrosis in vivo by phenotyping Abcb4 (ATP-binding cassette transporter, subfamily B, member 4) knockout (Abcb4−/−, also known as Mdr2−/−) mice, an established and highly reproducible model of sclerosing cholangitis [16–18].