Autoreactive Cd4+ Lkm–Specific and Anticlonotypic T–Cell Responses in Lkm–1 Antibody–Positive Autoimmune Hepatitis

Abstract

Peripheral blood mononuclear cells (PBMC) of patients with autoimmune hepatitis (AIH) and controls were studied for their proliferative response to six overlapping synthetic peptides covering the 33-amino acid immunodominant region of cytochrome P450IID6, the main target antigen of LKM-1 antibody-positive type II AIH. PBMC from 8 of 8 type II AIH patients (100%), 6 of 12 LKM-1 antibody-negative type I AIH patients (50%), but only 4 of 31 patients with chronic hepatitis C (12.9%) reacted with a 23-amino acid LKM peptide and mainly with a shorter 18-amino acid LKM peptide. Follow-up showed that LKM-specific T-cell responses decreased after immunosuppression had started. Fine specificity, HLA restriction, and cytokine release of LKM-specific T cells were analyzed with 16 CD4+ peptide-specific T-cell lines and 21 CD4+ T-cell clones isolated and expanded from blood and liver tissue of six AIH patients. Activated LKM-specific T cells released interferon gamma (IFN-gamma) but no or little interleukin-4. In three AIH patients, PBMC showed specific recognition of autologous LKM-specific T cells, suggesting the presence of a regulatory T-cell network. These T cells also showed the CD4+ phenotype and secreted large amounts of IFN-gamma. Furthermore, it was assessed that the regulatory T-cell response is clonotypic. To conclude, we describe a major T-cell epitope in AIH that was recognized by Th1 helper cells isolated from blood and liver tissue. This autoreactive T-cell response correlated widely with disease activity and LKM-1 antibody status and seemed to be regulated by anticlonotypic T cells.