Mucosal-associated invariant T (MAIT) cells, defined as CD3+ Valpha7.2+ CD161++ T lymphocytes, are central in the immunosurveillance, tissue maintenance and repair at mucosal sites.^{1 2} They are considered integral in protecting the biliary mucosa from microbiota due to their predominant location around the portal tracts.^{2 3} In autoimmune liver disease (AILD), MAIT cell cytokine production of interferon gamma (IFNγ), tumour necrosis factor alpha (TNF-α) and granzymes are significantly reduced compared to healthy subjects.^1–3 Furthermore, chronic MAIT cell activation predisposes the liver to the profibrotic state which was shown to be interleukin-17A (IL-17A) dependent in AILD³. The biological characteristics and functional activity of MAIT cells in children with AILD has not been investigated. We performed mass cytometry by CyTOF (Cytometry by Time of Flight) on peripheral blood mononuclear cells (PBMC) from children with AILD (AIH type 1, N=8, median age 14 yrs (range 9–14), and PSC, N=8, 14 yrs (range 12–15) and in healthy children (HC) (N=8, 12 yrs (range 5–15)). PBMCs treated with a cell stimulation cocktail of phorbol 12-myristate 13-acetate (PMA) and ionomycin were incubated for 4hours prior to downstream CyTOF investigation. Untreated paired PBMCs from the same patients were used as controls. MAIT cell and conventional CD3+ cytokine production, measured as the median metal intensity (MMI), were recorded. Our results show stimulated (STIM) blood MAIT cells from children with PSC had higher TNF-α production than AIH patients and healthy children (figure 1). Reduced MAIT cell Granzyme B and IFNy expression were observed from the AIH and PSC cohorts compared to HC. IL-17A production was induced in the 4hour incubation period, an observation not previously reported in adult MAIT cells which requires longer activation. The patients’ CD3+ T lymphocyte cytokine expression levels were also assessed and are presented for comparison. Of note, although the trend of CD3+ TNF-α production is similar, it is 20-fold less than observed in MAIT cells. No CD3+ IL-17A production is observed in all three cohorts. In conclusion, reduced IFNγ and Granzyme production in our paediatric AILD cohort is consistent with MAIT cell dysfunction described in adult AILD. However, higher MAIT cell TNF-α and IL-17A production in the PSC cohort following acute activation suggests TNF superfamily pathway preservation and a greater potential for early release of the chronic inflammatory cytokine IL-17A, both of which may contribute to autoimmune liver disease progression.

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Abstract OC53 Figure 1

Box – and- whisker plots showing the MAIT cell post-stimulation (STIM) response in paediatric patients with AIH N=8, PSC N=8 and in healthy children N=8. MAIT cell expression levels of the cytokines TNF-α, IFNy, Granzyme B and IL-17A are displayed in the top row. Their paired CD3+ post-STIM responses are shown in the bottom row

References

1. D’Souza C, Chen Z, Corbett A. Revealing the protective and pathogenic potential of MAIT cells. Mol Immunol. 2018 Nov;103:46–54.

2. Jeffery HC, van Wilgenburg B, Kurioka A. Biliary epithelium and liver B cells exposed to bacteria activate intrahepatic MAIT cells through MR1. J Hepatol. 2016 May;64(5):1118–1127.

3. Bottcher K, Rombouts K, Saffioti F. MAIT Cells are chronically activated in patients with autoimmune liver disease and promote profibrogenic hepatic stellate cell activation. Hepatology. 2018 Jul;68(1):172–186.