Background & aims: In hepatitis, hepatocytes gain the ability to express major histocompatibility complex (MHC) class II molecules and to present antigen to CD4 T cells. Here, we investigated whether MHC class II-expressing hepatocytes influence in vitro the differentiation of CD4 T cells and in vivo the T-cell response to and control of viral infection.
Methods: Class II transactivator-transgenic hepatocytes that constitutively express MHC class II molecules were used to stimulate CD4 T cells in vitro, and the effector response type of the stimulated CD4 T cells was determined. The in vivo relevance of the obtained findings was confirmed by infecting nontransgenic or class II transactivator-transgenic mice with lymphocytic choriomeningitis virus.
Results: MHC II-expressing hepatocytes induced T helper cell (Th) 2 differentiation of uncommitted CD4 T cells and abrogated the ability of previously differentiated Th1 to secrete interferon-gamma, even in the presence of proinflammatory microbial signals. The suppression of Th1 responses by hepatocytes was associated with poor expression levels of Th1-promoting Delta-like Notch ligands. In vivo, MHC II expression by hepatocytes impaired the interferon-gamma production by lymphocytic choriomeningitis virus-specific CD4 and CD8 T cells and prolonged viral persistence.
Conclusions: By instructing infiltrating CD4 T cells to differentiate into a less inflammatory phenotype, MHC II-expressing hepatocytes seem to impair antiviral CD8 T-cell responses and viral clearance. Thus, hepatocytes may contribute to the chronicity of hepatitis virus infection.