Table 1: Genetic factors related to vitamin D and primary biliary cirrhosis.

Primary biliary cirrhosis (PBC)Vitamin D

Human leukocyte antigen (HLA)HLA-DR expression increased in patients with PBC [2431]Calcitriol suppresses MHC class II antigen expression in human mononuclear phagocytes and decreases interferon-γ-induced HLA-DR antigen expression in normal and transformed human keratinocytes [3235]

Vitamin D receptor (VDR)(i) BsmI polymorphisms of VDR were associated with PBC in German, Hungarian, Japanese, Italian, and Chinese patients [3640]
(ii) In the Polish population, BsmI and TaqI polymorphisms were associated with the presence of advanced fibrosis/liver cirrhosis at the diagnosis of PBC [41]
(iii) VDR polymorphisms predicted a decreased bone mineral density in PBC patients [42, 43]

Toll-like receptors (TLRs)(i) The expression of TLR-3 was markedly increased in biliary epithelial cells (BECs) in areas of ductular reaction in liver diseases, including PBC [45](i) Calcitriol has been shown to down-regulate intracellular TLR-2, TLR-4, and TLR-9 expression in human monocytes [55]
(ii) The bile duct epithelial cells in PBC liver tissues markedly expressed TLR-4, which was also observed in periportal hepatocytes of PBC liver tissues and its expression was extended to interlobular hepatocytes in advanced-stage PBC [47](ii) TLR activation results in the expression of the VDR and 1α-vitamin D hydroxylase in human monocytes [56]
(iii) Biliary epithelial cells show intense immune reactivity for cathelicidin and for VDR [59]

Apolipoprotein E (ApoE)(i) The ApoE ε4 allele was suggested as a marker of disease severity in PBC [63](i) The LDL receptor on calcitriol-induced macrophages has been found to exhibit specificity for ApoB- and ApoE-containing lipoproteins [67]
(ii) The ε4 allele carriers demonstrated a poor response to ursodeoxycholic acid (UDCA) treatment [64](ii) Among ApoE knockout mice, those with dyslipidemia, high oxidative stress, and pronounced atherosclerosis after unilateral nephrectomy developed less plaque growth and calcification with vitamin D analog treatment (paricalcitol) [6068]

Nramp1 Novel alleles at a polymorphic microsatellite repeat region in the human NRAMP1 gene promoter were identified in patients with PBC [32]Calcitriol is known to stimulate phagocytosis and affects NRAMP1 transcription and protein expression in maturing phagocytes [78]

Cytotoxic T lymphocyte antigen-4 (CTLA-4)(i) PBC is known to be associated with polymorphisms of the CTLA-4 gene in Chinese, Japanese, Canadian, French, American Caucasian, and British patients but not in Brazilian patients [8086]
(ii) The meta-analysis suggests that the CTLA-4 gene may be a risk factor for PBC in Asians, while the AA genotype may be negatively associated with PBC [8789]
Calcitriol promoted regulatory T-cell profiles by increasing CTLA-4 and interleukin-10 in mouse colon protein extracts and stimulated the expression of high levels of CTLA-4 in human CD4+ CD25 T cells [95, 96]