Immunological relationship between autoimmune liver disease and autoimmune thyroid disease:a cross-sectional study

Background: High prevalence of autoimmune thyroid disease (AITD) in patients with autoimmune liver disease (AILD) has been observed. Data on the clinical relationship between AILD and AILD remain scanty. We aimed to evaluate the immunological relationship between AILD and AITD. Results: 324 patients with AILD were enrolled, 113 out of 324 patients were concurrent AITD (34.9%). Patients with autoimmune hepatitis (AIH) were more likely to develop AITD (45.8%), followed by autoimmune hepatitis-primary biliary cholangitis overlap syndrome (AIH-PBC OS) (39.5%) and PBC (22.6%). AILD patients with concurrent AITD showed higher levels of IgG (21.5 g/L vs 16.3 g/L, P<0.0001) and gamma globulin (γ-globulin)(27.1% vs 21.9%, P<0.0001), and IgG were positively correlated with thyroid antibodies thymoglobulinantibody (TGAb), thyroid peroxidase antibody (TPOAb) (r=0.396, 0.322; P<0.0001, P=0.002, respectively). The frequency of TPOAb positivity was highest in PBC patients with concurrent AITD (83.9%). The AIH concomitant with AITD had a higher nuclear homogenizing antinuclear antibody (ANA) positivity compared with the AIH alone (P=0.019). PBC patients with concurrent AITD were significantly older than the PBC patients without AITD (P=0.0004). Thyroid dysfunction in AILD patients with concurrent AITD was principally characterized by Hashimoto's thyroiditis (65.5%) and diffuse lesions were mainly indicated in thyroid ultrasound (53.1%). Conclusions: The high incidence of AILD concomitant with AITD, as well as the higher levels of serum IgG and γ-globulin, and the strong correlation between thyroid antibody and IgG, suggesting that we should strengthen the screening immunoglobulin

Immunological relationship between autoimmune liver disease and autoimmune thyroid disease:a cross-sectional study CURRENT

Background
Autoimmune liver disease (AILD), caused by the imbalance of immune tolerance and leading to liver and gallbladder system damage, is a group of autoimmune diseases. The spectrum of AILD includes autoimmune hepatitis (AIH), primary biliary cholangitis (PBC), primary sclerosing cholangitis (PSC), and overlap syndrome (OS). Autoimmune thyroid diseases (AITD), featured by the production of autoantibody which induced by abnormal autoimmune responses and targets thyroid cells, is a class of organ-specific autoimmune disease, and mainly including Hashimoto's thyroiditis (HT) and Graves' disease (GD). AILD frequently overlap other extrahepatic autoimmune disease (EHAID) [1][2][3], AITD is the commonest concurrent EHAID in AILD patients (10-23%) [4][5][6]. The high incidence of AILD concomitant with AITD may be closely relevant to its underlying pathogenesis. Dr. Daya CM [7]proposed the concept of molecular mimicry, that is, infection with a virus or bacterium that contains a protein similar to a thyroid protein may result in the activation of thyroid-specific T cells, triggering immune system disorders and giving rise to thyroid dysfunction. Whether hepatocytes or cholangiocytes and thyroid cell have similar proteins, which cross-react with each other and activate specific T cells, leading to the concurrence of AILD and AITD, remains yet to be determined.
The incidence rate, clinical features, and outcomes in AILD patients concomitant with EHAID have been analyzed by previous studies [8][9][10][11][12][13][14][15]. No targeted study on the correlation between AITD and AILD has been conducted. Therefore, our study intends to analyze the differences in biochemical and immunological indicators between AILD patients with and without AITD and to explore the possible association of clinical immunology between the two diseases.

Patient selection
Retrospectively recruited 324 inpatients with AILD at Department of Hepatology, Tianjin Associated diagnosis of EHAID and family history of autoimmune diseases were searched and retrieved via the hospital electronic records, clinical letters and medical case notes.
All these diseases have been diagnosed and confirmed based on the international criteria.
The diagnosis of GD was based on the American Thyroid Association Guidelines for Diagnosis and Management of Hyperthyroidism and Other Causes of Thyrotoxicosis (2016) [20]. The diagnosis of HT was based on the Chinese Guidelines for diagnosis and treatment of Adult Hypothyroidism (2017) [21].

Laboratory methods
Patients' case records, such as age, sex, symptoms, personal and family history, were Thyroid ultrasounds were performed by a well-trained physician (PHILIPSIU22, Netherlands).
A liver biopsy was performed in 187 patients with AILD. Histological assessment of the severity of liver inflammation and the degree of fibrosis was based on the scoring system proposed by Batts and Ludwig [22]. Biopsies were evaluated by two experienced pathologists that were unaware of the subjects' identity or clinical information.

Statistical analysis
Results were analyzed using SPSS version 23.0 (IBM Corp, USA). Continuous variables satisfied normality were expressed as mean±standard deviation (x±SD), and Student ttest was used to compare the differences in variable between the two groups.

Immunological indicators
AILD patients with concurrent AITD showed higher levels of IgG (21.5 g/L vs 16.3 g/L, P<0.0001) and γ-globulin (27.1% vs 21.9%, P<0.0001). (Table 5) The serum IgG levels in the three subgroups of AILD patients with concurrent AITD was higher than those of patients without concurrent AITD (

Autoantibody profile
No significant differences were observed in ANA between PBC/AIH-PBC OS patients with and without AITD (P>0.05) ( Table 3, Table 4). But the nuclear homogenous ANA between AIH patients with and without AITD was excluded ( P=0.019). ( Table 2)

Thyroid function
Thyroid dysfunction were mainly manifest as Hashimoto's thyroiditis and thyroid antibody positivity in AILD concomitant with AITD, and ultrasound indicated diffuse thyroid lesions.
The frequency of TPOAb positivity differed significantly among the three subgroups of  Similarly, the levels of IgG and γ-globulin in AILD concomitant with AITD were higher than those in AILD alone, and IgG in the three subgroups of AILD patients with concurrent AITD was higher than those of patients without concurrent AITD as well. Further exploration of the correlation between IgG and thyroid antibodies revealed a positive correlation. It is possible, therefore, that presence of AITD could increase serum levels of IgG. Meanwhile, some AILD patients with concurrent AITD had undergone or were undergoing antithyroid or immunosuppressive therapy. Related literature has established that anti-thyroid therapy reduces thyroid antibody titers [30], signifying that IgG may be higher before controlling especially in PBC individuals, once IgG was found to be elevated dramatically, not only AIH-PBC overlap but also closely monitoring of thyroid function should be considered.
This study revealed that nuclear homogenization ANA positivity was more prevalent in AIH concomitant with AITD compared to AIH alone. However, the result may be limited by the retrospective and small sample sizes of this study, whereby considerable multicenter and prospective cohort is necessary to estimate the probability. No statistical significance in other autoantibodies was attained between AILD patients with and without AITD, indicating that the specificity of autoantibodies in thyroid diseases was not evident and the screening of AITD susceptible individuals in AILD merely by certain autoantibodies was inappropriate.
Our study observed that the TPOAb positivity was the highest in PBC patients with concurrent AITD compared with other AILD patients with concurrent AITD, which was in parallel with Nakamura H's findings [31]. Nevertheless, further research remains to be carried out whether it can be identified as a serological clue to distinguish AIH from PBC when the diagnosis is equivocal. Consequently, we set about exploring the expression of TPO (a membrane-bound glycoprotein containing a heme prosthetic group) and cholangiocytes surface proteins to establish a probable interplay of molecular mechanism. Interestingly, our data showed that AITD more frequently coincided with AILD's onset or occurred years after the diagnosis of AILD, which was conflict with Guan-Wee Wong's [6] findings that EHAID predated AIH diagnosis. Actually, controversy still exists on the above results. Firstly, Thyroid abnormality was unveiled by accident during active stages of hepatitis, which was ignored or missed in previous clinical practice. Secondly, Patients, prior to AILD, who have suffered from thyroid disease and have accepted antithyroid therapy, whereas the liver function was not systematically screened then. After all, AILD tended to be asymptomatic at presentation. Lastly, it's well-recognized that patients with autoimmune disease are prone to involve multiple organs, liver and thyroid might be affected simultaneously or successively. As a consequence, an uncertain sequence still exists in AILD and AITD. Meanwhile, the selection bias cannot be avoided, opinions on the onset time of disease vary from hepatologists to endocrinologists. Hence, it is of vital importance to strengthen the consultation between hepatologist and endocrinologist and promote the development of the MDT diagnosis and treatment model.

Conclusions
In summary, AITD was found to be the most prevalent concurrent autoimmune disease in AILD patients with concurrent EHAID. It seems reasonable to recommend routine screening for autoimmune thyroid disease in patients with AILD when IgG and γ-globulin were significantly elevated.

Funding
This research received no specific grant from any funding agency.

Availability of data and materials
All data and analysis results are included in this article. The datasets used and/or analyzed during the current study are available from the corresponding author on reasonable request.

Author'contributions
Jia

Ethics approval and consent to participate
The study was approved by the Ethics Committee of Tianjin Second People's Hospital.
Written informed consent was obtained from all study participants.

Consent for publication
Not applicable. EHAID, extrahepatic autoimmune disease; AILD, autoimmune liver disease; AITD, autoimmune thyroid disease; HT, Hashimoto's thyroiditis; GD, Graves' disease. Data were shown as mean ± SD and/or median (range).  Data were shown as mean ± SD and/or median (range).