Crosstalk between type II NKT cells and T cells leads to spontaneous chronic inflammatory liver disease.

Background & Aim: Natural killer T (NKT) cells are CD1d-restricted innate-like T cells that modulate innate and adaptive immune responses. Unlike the well-characterized invariant/type I NKT cells, type II NKT cells with a diverse T cell receptor repertoire are poorly understood. This study defines the pathogenic role of type II NKT cells in the etiology of chronic liver inflammation.

Methods: Transgenic mice with the Lck promoter directing CD1d overexpression on T cells in Jα18 wild-type (Lck-CD1dTgJα18; type I NKT cell sufficient) and Jα18-deficient (Lck-CD1dTgJα18, type I NKT cell deficient) mice were analyzed for liver pathology and crosstalk between type II NKT cells and conventional T cells. CD1d expression on T cells in peripheral blood samples and liver sections from autoimmune hepatitis patients and healthy individuals were also examined.

Results: Lck-CD1dTgJα18 and Lck-CD1dTgJα18 mice developed similar degrees of liver pathology resembling chronic autoimmune hepatitis in humans. Increased CD1d expression on T cells promoted the activation of type II NKT cells and other T cells. This resulted in T1-skewing and impaired T2 cytokine production in type II NKT cells. Dysfunction of type II NKT cells was accompanied by conventional T cell activation and pro-inflammatory cytokine production, leading to a hepatic T/B lymphocyte infiltration, elevated autoantibodies and hepatic injury in Lck-CD1dTg mice. A similar mechanism could be extended to humans as CD1d expression is upregulated on activated human T cells and increased presence of CD1d-expressing T cells was observed in autoimmune hepatitis patients.

Conclusions: Our data reveals enhanced crosstalk between type II NKT cells and conventional T cells, leading to a T1-skewed inflammatory milieu, and consequently, to the development of chronic autoimmune liver disease. Lay summary: CD1d overexpression on T cells enhances crosstalk between type II NKT cells and T cells, resulting in their aberrant activation and leading to the development of chronic autoimmune liver disease.