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^o, 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^o 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 T_h1-skewing and impaired T_h2 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 T_h1-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.