Failure of thymic deletion and instability of autoreactive Tregs drive autoimmunity in immune-privileged liver.

The liver is an immune-privileged organ that can deactivate autoreactive T cells. Yet in autoimmune hepatitis (AIH), autoreactive T cells can defy hepatic control and attack the liver. To elucidate how tolerance to self-antigens is lost during AIH pathogenesis, we generated a spontaneous mouse model of AIH, based on recognition of an MHC class II-restricted model peptide in hepatocytes by autoreactive CD4+ T cells. We found that the hepatic peptide was not expressed in the thymus, leading to deficient thymic deletion and resulting in peripheral abundance of autoreactive CD4+ T cells. In the liver, autoreactive CD4+ effector T cells accumulated within portal ectopic lymphoid structures and maturated toward pathogenic IFN-γ and TNF coproducing cells. Expansion and pathogenic maturation of autoreactive effector T cells was enabled by a selective increase of plasticity and instability of autoantigen-specific Tregs but not of nonspecific Tregs. Indeed, antigen-specific Tregs were reduced in frequency and manifested increased IL-17 production, reduced epigenetic demethylation, and reduced expression of Foxp3. As a consequence, autoantigen-specific Tregs had a reduced suppressive capacity, as compared with that of nonspecific Tregs. In conclusion, loss of tolerance and the pathogenesis of AIH were enabled by combined failure of thymic deletion and peripheral regulation.

Update of the simplified criteria for autoimmune hepatitis: Evaluation of the methodology for immunoserological testing.

BACKGROUND & AIMS: The simplified criteria for the diagnosis of autoimmune hepatitis (AIH) include immunofluorescence testing (IFT) of antinuclear and smooth muscle autoantibodies (ANA and SMA) on rodent tissue sections. We aimed to establish scoring criteria for the implementation of ANA IFT on human epithelioma-2 (HEp-2) cells and ELISA-based testing. METHODS: ANA and SMA reactivity of 61 AIH sera and 72 non-alcoholic fatty liver disease controls were separately assessed on tissue sections and HEp-2 cells to compare the diagnostic value at increasing titers. A total of 113 patients with AIH at diagnosis and 202 controls from 3 European centers were assessed by IFT as well as 3 different commercially available ANA ELISA and 1 anti-F-actin ELISA. RESULTS: ANA assessment by IFT on liver sections had 83.6% sensitivity and 69.4% specificity for AIH at a titer of 1:40. On HEp-2 cells, sensitivity and specificity were 75.4% and 73.6%, respectively, at an adjusted titer of 1:160. Area under the curve (AUC) values of ANA ELISA ranged from 0.70-0.87, with ELISA coated with HEp-2 extracts in addition to selected antigens performing significantly better. SMA assessment by IFT had the highest specificity for the SMA-VG/T pattern and anti-microfilament reactivity on HEp-2 cells. ELISA-based anti-F-actin evaluation was a strong predictor of AIH (AUC 0.88) and performed better than SMA assessment by IFT (AUC 0.77-0.87). CONCLUSION: At adjusted cut-offs, both ANA IFT using HEp-2 cells and ELISA-based autoantibody evaluation for ANA and SMA are potential alternatives to tissue-based IFT for the diagnosis of AIH. LAY SUMMARY: Autoantibodies are a hallmark of autoimmune hepatitis and are traditionally tested for by immunofluorescence assays on rodent tissue sections. Herein, we demonstrate that human epithelioma cells can be used as a reliable substrate for immunofluorescence testing. ELISA-based testing is also a potentially reliable alternative for autoantibody assessment in autoimmune hepatitis. We propose the implementation of these testing methods into the simplified criteria for the diagnosis of autoimmune hepatitis.

TNF-Producing Th1 Cells Are Selectively Expanded in Liver Infiltrates of Patients with Autoimmune Hepatitis.

Autoimmune hepatitis (AIH) is a chronic inflammatory liver disease that is believed to be driven by a CD4+ T cell response to liver Ags. However, the pathogenic function of CD4+ effector T cells in AIH is not fully understood. To characterize liver-infiltrating lymphocytes in AIH, we determined the cytokine production of infiltrating cells obtained from biopsy material by quantitative RT-PCR and flow cytometry. A cytokine quantitiative RT-PCR array of AIH specimens revealed that TNF was the most strongly upregulated cytokine, as compared with control livers. To confirm this finding, we determined the frequencies of TNF-producing CD4+ T cells in peripheral blood and in liver biopsy specimens in comparison with those of CD4+ T cells producing IFN-γ or IL-17. In AIH, TNF-producing CD4+ T cells were significantly expanded, both in blood and liver, whereas IL-17-producing CD4+ T cells were not. However, the majority of the TNF-producing CD4+ T cells in AIH also produced IFN-γ, suggesting that TNF producers might represent a pathogenic activation state of Th1 cells. Ag-specific stimulation of PBMC from AIH patients with the AIH-associated autoantigen SEPSECS resulted in significant TNF production only in patients manifesting SLA/LP autoantibodies targeting SEPSEC but not in healthy individuals who do not manifest this reactivity. Taken together, our findings indicated that TNF-producing CD4+ T cells are expanded in AIH, both in blood and in liver. TNF-producing CD4+ T cells in AIH seem to be aberrantly activated Th1 cells. Our findings provide a rationale for therapeutic efforts using TNF blockade in AIH.

The 5'-nucleotidase S5nA is dispensable for evasion of phagocytosis and biofilm formation in Streptococcus pyogenes.

5'-nucleotidases are widespread among all domains of life. The enzymes hydrolyze phosphate residues from nucleotides and nucleotide derivatives. In some pathobiontic bacteria, 5'-nucleotidases contribute to immune evasion by dephosphorylating adenosine mono-, di-, or tri-phosphates, thereby either decreasing the concentration of pro-inflammatory ATP or increasing the concentration of anti-inflammatory adenosine, both acting on purinergic receptors of phagocytic cells. The strict human pathogen Streptococcus pyogenes expresses a surface-associated 5'-nucleotidase (S5nA) under infection conditions that has previously been discussed as a potential virulence factor. Here we show that deletion of the S5nA gene does not significantly affect growth in human blood, evasion of phagocytosis by neutrophils, formation of biofilms and virulence in an infection model with larvae of the greater wax moth Galleria mellonella in S. pyogenes serotypes M6, M18 and M49. Hence, the surface-associated 5'-nucleotidase S5nA seems dispensable for evasion of phagocytosis and biofilm formation in S. pyogenes.