J Clin Med Res

Journal of Clinical Medicine Research, ISSN 1918-3003 print, 1918-3011 online, Open Access

Article copyright, the authors; Journal compilation copyright, J Clin Med Res and Elmer Press Inc

Journal website http://www.jocmr.org

Review

Volume 5, Number 6, December 2013, pages 407-415

The Role of Vitamin D in Autoimmune Hepatitis

**Table 1.** Genetic Factors Related to Vitamin D and Autoimmune Hepatitis (AIH)
Autoimune Hepatitis (AIH)	Vitamin D
Human Leukocyte Antigen (HLA)
DRB10301* and DRB10401* are the susceptibility genes for type 1 AIH in Caucasian American, northern European, and Italian patients, whereas, DRB11501-DRB50101 protects against type 1 AIH in adult Caucasian Americans. DRB10405* allele is associated with the susceptibility to type 1 AIH in Japanese, Chinese, and Mexican patients. DRB11301* is associated with type 1 AIH in Argentine children, Brazilian patients, Venezuelan patients, and Indian patients. Susceptibility to type 2 AIH has been associated DRB107* in Brazil, Germany, and Turkish children. In a systematic review and meta-analysis study in Latin America, DQB102, DQB10603, DRB10405, and DRB11301 alleles were found to be risk factors for AIH, while DRB11302* and DQB10301* alleles were protective factors for AIH.	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.
Vitamin D Receptor (VDR)
BsmI and TaqI are reported to be associated with autoimmune liver diseases. The FokI polymorphisms of VDR are linked to AIH German and Chinese populations.
Cytotoxic T lymphocyte antigen-4 (CTLA-4)
The mRNA levels of CTLAA were significantly decreased in patients with AIH compared with healthy controls. Mice vaccinated with a plasmid containing the N-terminal regional of mouse CTLA-4 and the antigenic region of human CYP2D6 developed anti-LKM1 and anti-LC1 antibodies of IgG2 subclass. In addition, the ALT levels correlated with both the presence of anti-LKM1/anti-LC1 antibodies and presence of liver necroinflammation. CTLA-4 deficiency causes severe lympho-proliferative disorder and multi-organ auto-immunity, leading to massive tissue destruction and early death. CTLA-4 Ig suppressed a lupus-like illness in mouse models and reduced the incidence of diabetes in NOD mice. CTLA-4 polymorphisms are associated with type 1 AIH in northern Caucasian European [53], Chinese patients, and Argentina children; but not in Brazilian, Japanese, German populations. A meta-analysis study demonstrated that CTLA-4 gene +49A/G polymorphisms may be associated with the susceptibility to patients with type 1 AIH, while A/A genotype may be protective against type 1 AIH.	Calcitriol promoted regulatory T cell profiles by increasing CTLA-4 and interleukin-10 in mouse colon protein extracts. Calcitriol also stimulated the expression of high levels of CTLA-4 in human CD4⁺ CD25^- T cells.
Toll-like Receptors (TLRs)
In ConA-induced mouse AIH models, TLRs-My88 signaling accelerates the liver damage, whereas a decrease in CpG-containing oligodeoxynucleotides (CpG-ODN) treatment attenuates ConA-induced mouse AIH. CpG-ODN is a ligand for TLR-9 and is used as an immunological adjuvant. LR-3 also has an important role in liver inflammation and jury in ConA-induced mouse AIH models. In AIH, monocytes were higher in number, displayed a higher tumor necrosis factor alpha (TNF-α), and expressed high levels of TLR-4 compared with healthy controls.	Calcitriol has been shown to down-regulate intracellular TLR-2, TLR-4 and TLR-9 expression in human monocytes. TLR activation results in the expression of the VDR and 1α-vitamin D hydroxylase in human monocytes. Biliary epithelial cells show intense immune-reactivity for cathelicidin and VDR.
Cytochrome P450 Cyp2D6
CYP2D6 is the major target auto-antigen of LKM-1 and expressed on plasma membrane of hepatocytes, suggesting a pathogenic role for anti-LKM-1 in liver injury as a trigger. Anti-LKM-1 sera inhibited CYP2D6 activity in vitro but did not inhibit cellular drug metabolism in vivo. Antibodies against CYP2D6 conformational antigenic sites were present in LKM-1-positive sera.	CYP2D6 is a potential 25 hydroxyvitamin D-1 α-hydroxylase, which converts vitamin D₃ into 25OHD, and vitamin D 25-hydroxylase deficiency resulted in vitamin D deficiency. Human 25-hydroxyvitamin D-1 α-hydroxylase mutations also cause vitamin D-dependent rickets type 1.
Regulatory T cells (Tregs) and the forkhead/winged helix transcription factor 3 (Foxp3)
In humans, mutations in Foxp3 result in an auto-immune syndrome termed IPEX (immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome), an X-linked immuno-deficiency syndrome characterized by insulin-dependent diabetes, thyroiditis, massive T cell infiltration in multiple organs, and chronic wasting. During active disease, CD4⁺CD25^high T cells were fewer, expressed low levels of Foxp3, and were less effective at inhibiting target cell proliferation in patients with AIH than healthy controls. The Foxp3-positive cells were primarily located in hepatic lobular peri-sinusoidal spaces and the portal tract. The frequency of Tregs was increased in AIH patients compared with control and correlated with the inflammatory activity of the liver.	Vitamin D supplement was associated with significantly increased Tregs frequency in apparent healthy individuals. Calcitriol can affect human immune responses by regulating Foxp3 expression in CD4⁺ T cells through direct VDR binding to the Foxp3 gene. Calcitriol stimulated expression of high levels of CTLA-4 and Foxp3 in activated T cells.

Table 1. Genetic Factors Related to Vitamin D and Autoimmune Hepatitis (AIH)

Autoimune Hepatitis (AIH)

Vitamin D

Human Leukocyte Antigen (HLA)

DRB1*0301 and DRB1*0401 are the susceptibility genes for type 1 AIH in Caucasian American, northern European, and Italian patients, whereas, DRB1*1501-DRB5*0101 protects against type 1 AIH in adult Caucasian Americans.
DRB1*0405 allele is associated with the susceptibility to type 1 AIH in Japanese, Chinese, and Mexican patients.
DRB1*1301 is associated with type 1 AIH in Argentine children, Brazilian patients, Venezuelan patients, and Indian patients.
Susceptibility to type 2 AIH has been associated DRB1*07 in Brazil, Germany, and Turkish children.
In a systematic review and meta-analysis study in Latin America, DQB1*02, DQB1*0603, DRB1*0405, and DRB1*1301 alleles were found to be risk factors for AIH, while DRB1*1302 and DQB1*0301 alleles were protective factors for AIH.

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.

Vitamin D Receptor (VDR)

BsmI and TaqI are reported to be associated with autoimmune liver diseases.
The FokI polymorphisms of VDR are linked to AIH German and Chinese populations.

Cytotoxic T lymphocyte antigen-4 (CTLA-4)

The mRNA levels of CTLAA were significantly decreased in patients with AIH compared with healthy controls.
Mice vaccinated with a plasmid containing the N-terminal regional of mouse CTLA-4 and the antigenic region of human CYP2D6 developed anti-LKM1 and anti-LC1 antibodies of IgG2 subclass. In addition, the ALT levels correlated with both the presence of anti-LKM1/anti-LC1 antibodies and presence of liver necroinflammation.
CTLA-4 deficiency causes severe lympho-proliferative disorder and multi-organ auto-immunity, leading to massive tissue destruction and early death.
CTLA-4 Ig suppressed a lupus-like illness in mouse models and reduced the incidence of diabetes in NOD mice.
CTLA-4 polymorphisms are associated with type 1 AIH in northern Caucasian European [53], Chinese patients, and Argentina children; but not in Brazilian, Japanese, German populations.
A meta-analysis study demonstrated that CTLA-4 gene +49A/G polymorphisms may be associated with the susceptibility to patients with type 1 AIH, while A/A genotype may be protective against type 1 AIH.

Calcitriol promoted regulatory T cell profiles by increasing CTLA-4 and interleukin-10 in mouse colon protein extracts.
Calcitriol also stimulated the expression of high levels of CTLA-4 in human CD4⁺ CD25^- T cells.

Toll-like Receptors (TLRs)

In ConA-induced mouse AIH models, TLRs-My88 signaling accelerates the liver damage, whereas a decrease in CpG-containing oligodeoxynucleotides (CpG-ODN) treatment attenuates ConA-induced mouse AIH. CpG-ODN is a ligand for TLR-9 and is used as an immunological adjuvant.
LR-3 also has an important role in liver inflammation and jury in ConA-induced mouse AIH models.
In AIH, monocytes were higher in number, displayed a higher tumor necrosis factor alpha (TNF-α), and expressed high levels of TLR-4 compared with healthy controls.

Calcitriol has been shown to down-regulate intracellular TLR-2, TLR-4 and TLR-9 expression in human monocytes.
TLR activation results in the expression of the VDR and 1α-vitamin D hydroxylase in human monocytes.
Biliary epithelial cells show intense immune-reactivity for cathelicidin and VDR.

Cytochrome P450 Cyp2D6

CYP2D6 is the major target auto-antigen of LKM-1 and expressed on plasma membrane of hepatocytes, suggesting a pathogenic role for anti-LKM-1 in liver injury as a trigger.
Anti-LKM-1 sera inhibited CYP2D6 activity in vitro but did not inhibit cellular drug metabolism in vivo.
Antibodies against CYP2D6 conformational antigenic sites were present in LKM-1-positive sera.

CYP2D6 is a potential 25 hydroxyvitamin D-1 α-hydroxylase, which converts vitamin D₃ into 25OHD, and vitamin D 25-hydroxylase deficiency resulted in vitamin D deficiency.
Human 25-hydroxyvitamin D-1 α-hydroxylase mutations also cause vitamin D-dependent rickets type 1.

Regulatory T cells (Tregs) and the forkhead/winged helix transcription factor 3 (Foxp3)

In humans, mutations in Foxp3 result in an auto-immune syndrome termed IPEX (immune dysregulation, polyendocrinopathy, enteropathy, X-linked syndrome), an X-linked immuno-deficiency syndrome characterized by insulin-dependent diabetes, thyroiditis, massive T cell infiltration in multiple organs, and chronic wasting.
During active disease, CD4⁺CD25^high T cells were fewer, expressed low levels of Foxp3, and were less effective at inhibiting target cell proliferation in patients with AIH than healthy controls.
The Foxp3-positive cells were primarily located in hepatic lobular peri-sinusoidal spaces and the portal tract.
The frequency of Tregs was increased in AIH patients compared with control and correlated with the inflammatory activity of the liver.

Vitamin D supplement was associated with significantly increased Tregs frequency in apparent healthy individuals.
Calcitriol can affect human immune responses by regulating Foxp3 expression in CD4⁺ T cells through direct VDR binding to the Foxp3 gene.
Calcitriol stimulated expression of high levels of CTLA-4 and Foxp3 in activated T cells.

**Table 2.** Summary of the Non-Genomic Role of Vitamin D in Autoimmune Hepatitis
Autoimmune Hepatitis (AIH)	Vitamin D
The mitogen-activated protein kinase (MAPK) signaling pathways
The activation of p38 MAPK signaling pathway was up-regulated in experimental AIH, and the inhibition of p38 MAPK reduced hepatic inflammation and injury. IL-17 contributes to the pathogenesis of AIH via the induction of MAPK signaling pathway. Apolipoprotein A2 (Apo A2) suppressed ConA-induced hepatitis by inhibiting the phosphorylation of ERK1/2 and cJun and reduced the intra-hepatic infiltration of inflammatory cells.	Up-regulation of MAPK phosphatase 1 by vitamin D inhibited LPS-induced p38 activation and cytokine production in monocytes and macrophages.
γδT cells
An elevation in the relative and absolute counts of γδT cells in peripheral and portal areas of patients with AIH. AIH children are associated with an expansion and activation of γδT cells in the peripheral blood.	Calcitriol significantly inhibits the pro-inflammatory activity of γδT cells in a dose dependent fashion.
Interferon-gamma (IFN-γ)
Soluble liver antigen-specific IFN-γ responses were significantly more frequent in AIH patients. This response was positively correlated with transaminase levels and decreases with immune-suppressive treatment or disease in remission state. Production of IFN-γ is needed for the pathogenesis in a mouse model of fulminant liver inflammation and murine model of hepatitis.	Calcitriol decreased the serum ALT levels and markedly attenuated the histological liver damage, and reduction of IFN-γ in ConA-induced hepatitis. Calcitriol inhibits CD40-induced IFN-γ and immune-modulatory activity in human monocytes and is a potent suppressor of IFN-γ-mediated macrophage activation.
Reactive Oxygen Species (ROS)
The amount of ROS found in AIH livers was significantly higher than in healthy human livers. Markers of lipid peroxidation were significantly elevated in patients with AIH compared with normal controls. Red blood cell glutathione (GSH) concentrations were significantly lower in AIH than normal controls, but plasma GSH peroxidase activity was significantly higher in AIH patients with elevated ALT values compared with normal controls. Homologs of NADPH oxidases (NOXs) are major sources of ROS and was expressed in human livers with stage 2-3 AIH.	Vitamin D may reduce the extent of lipid peroxidation, induces SOD activity in the hepatic antioxidant system in rats, enhances intracellular GSH pools, and significantly reduces nitrite production induced by lipopolysaccharide (LPS). In rat centrilobular hepatocytes, a vitamin D-deficient diet induced a significant increase in NADPH.
Nitric oxide synthase (NOS)
NO production in both serum and liver tissue increased in the liver injury induced by delayed-type hypersensitivity to picryl chloride. Both endogenous and exogenous NO protected liver against CoA-induced liver injury. Increased iNOS expression and nitrotyrosine accumulation correlated with the histological severity of AIH.	Calcitriol-produced by macrophages may provide protection against the oxidative injuries caused by NO burst. Calcitriol is known to inhibit lipopolysaccharides (LPS)-induced immune activation in human endothelial cells.

Table 2. Summary of the Non-Genomic Role of Vitamin D in Autoimmune Hepatitis

Autoimmune Hepatitis (AIH)

Vitamin D

The mitogen-activated protein kinase (MAPK) signaling pathways

The activation of p38 MAPK signaling pathway was up-regulated in experimental AIH, and the inhibition of p38 MAPK reduced hepatic inflammation and injury.
IL-17 contributes to the pathogenesis of AIH via the induction of MAPK signaling pathway.
Apolipoprotein A2 (Apo A2) suppressed ConA-induced hepatitis by inhibiting the phosphorylation of ERK1/2 and cJun and reduced the intra-hepatic infiltration of inflammatory cells.

Up-regulation of MAPK phosphatase 1 by vitamin D inhibited LPS-induced p38 activation and cytokine production in monocytes and macrophages.

γδT cells

An elevation in the relative and absolute counts of γδT cells in peripheral and portal areas of patients with AIH.
AIH children are associated with an expansion and activation of γδT cells in the peripheral blood.

Calcitriol significantly inhibits the pro-inflammatory activity of γδT cells in a dose dependent fashion.

Interferon-gamma (IFN-γ)

Soluble liver antigen-specific IFN-γ responses were significantly more frequent in AIH patients. This response was positively correlated with transaminase levels and decreases with immune-suppressive treatment or disease in remission state.
Production of IFN-γ is needed for the pathogenesis in a mouse model of fulminant liver inflammation and murine model of hepatitis.

Calcitriol decreased the serum ALT levels and markedly attenuated the histological liver damage, and reduction of IFN-γ in ConA-induced hepatitis.
Calcitriol inhibits CD40-induced IFN-γ and immune-modulatory activity in human monocytes and is a potent suppressor of IFN-γ-mediated macrophage activation.

Reactive Oxygen Species (ROS)

The amount of ROS found in AIH livers was significantly higher than in healthy human livers.
Markers of lipid peroxidation were significantly elevated in patients with AIH compared with normal controls.
Red blood cell glutathione (GSH) concentrations were significantly lower in AIH than normal controls, but plasma GSH peroxidase activity was significantly higher in AIH patients with elevated ALT values compared with normal controls.
Homologs of NADPH oxidases (NOXs) are major sources of ROS and was expressed in human livers with stage 2-3 AIH.

Vitamin D may reduce the extent of lipid peroxidation, induces SOD activity in the hepatic antioxidant system in rats, enhances intracellular GSH pools, and significantly reduces nitrite production induced by lipopolysaccharide (LPS).
In rat centrilobular hepatocytes, a vitamin D-deficient diet induced a significant increase in NADPH.

Nitric oxide synthase (NOS)

NO production in both serum and liver tissue increased in the liver injury induced by delayed-type hypersensitivity to picryl chloride.
Both endogenous and exogenous NO protected liver against CoA-induced liver injury.
Increased iNOS expression and nitrotyrosine accumulation correlated with the histological severity of AIH.

Calcitriol-produced by macrophages may provide protection against the oxidative injuries caused by NO burst.
Calcitriol is known to inhibit lipopolysaccharides (LPS)-induced immune activation in human endothelial cells.