Identification of HLA-A2-restricted CD8(+) cytotoxic T cell responses in primary biliary cirrhosis: T cell activation is augmented by immune complexes cross-presented by dendritic cells

Constitutive versus activation-dependent cross-presentation of immune complexes by CD8(+) and CD8(-) dendritic cells in vivo

Murine splenic dendritic cells (DCs) can be divided into two subsets based on CD8alpha expression, but the specific role of each subset in stimulation of T cells is largely unknown. An important function of DCs is the ability to take up exogenous antigens and cross-present them in the context of major histocompatibility complex (MHC) class I molecules to CD8(+) T cells. We previously demonstrated that, when cell-associated ovalbumin (OVA) is injected into mice, only the CD8(+) DC subset cross-presents OVA in the context of MHC class I. In contrast to this selectivity with cell-associated antigen, we show here that both DC subsets isolated from mice injected with OVA/anti-OVA immune complexes (OVA-IC) cross-present OVA to CD8(+) T cells. The use of immunoglobulin G Fc receptor (Fc(gamma)R) common gamma-chain-deficient mice revealed that the cross-presentation by CD8(-) DCs depended on the expression of gamma-chain-containing activating FcgammaRs, whereas cross-presentation by CD8(+) DCs was not reduced in gamma-chain-deficient mice. These results suggest that although CD8(+) DCs constitutively cross-present exogenous antigens in the context of MHC class I molecules, CD8(-) DCs only do so after activation, such as via ligation of Fc(gamma)Rs. Cross-presentation of immune complexes may play an important role in autoimmune diseases and the therapeutic effect of antitumor antibodies.

The immunology of primary biliary cirrhosis: the end of the beginning?

The chronic liver disease primary biliary cirrhosis (PBC) is characterised by autoreactive B-cell and T-cell responses directed against mitochondrial antigens. In recent years these responses have been extensively characterised and the principal PBC associated autoantigen identified as pyruvate dehydrogenase complex (PDC). The identification of anti-PDC responses (present in over 95% of PDC patients) has given rise to important questions pertinent to our understanding of the pathogenesis of PBC. What specific role to anti-PDC responses play in target cell damage? How and why does immune tolerance break down to as highly conserved and ubiquitously expressed self-antigen as PDC? Why does breakdown in tolerance to an antigen present in all nucleated cells result in damage restricted to the intra-hepatic bile ducts? In attempting to answer these key questions we have, in this review, proposed a unifying hypothesis for the pathogenesis of PBC.

Interactions between dead cells and dendritic cells in the induction of antiviral CTL responses

Dendritic cells - professional antigen-presenting cells - are key players for activating adaptive immune responses against viruses. Apoptosis or lytic cell death often accompanies viral infection. Dendritic cells can acquire infected dead or dying cells as exogenous sources of antigens for presentation on MHC class I and II molecules to initiate T cell responses. This pathway of activating T cells may be critical for the development of effective antiviral immunity in vivo.

Autoreactive CD8 T cells in organ-specific autoimmunity: emerging targets for therapeutic intervention

The importance of CD8 T cells in the pathogenesis of organ-specific autoimmune diseases has not previously been well recognized. Recent evidence, however, indicates that autoreactive CD8 T cells can contribute substantially to tissue damage in both murine and human autoimmune disorders. As such, these T cells now become an attractive target for therapeutic intervention.

Quantitative and functional analysis of PDC-E2-specific autoreactive cytotoxic T lymphocytes in primary biliary cirrhosis

While the pathologic mechanisms responsible for organ-specific tissue damage in primary biliary cirrhosis (PBC) remain an enigma, it has been suggested that the pathology is mediated by autoreactive T cells infiltrating the intrahepatic bile ducts. Previously, we have documented that there is 100-fold enrichment in the frequency of CD4(+) autoreactive T cells in the liver that are specific for peptides encoded by the E2 components of the pyruvate dehydrogenase complexes (PDC-E2). We have also recently characterized the first MHC class I-restricted epitope for PDC-E2, namely amino acid 159-167, a region very similar to the epitope recognized by MHC class II-restricted CD4(+) cells and by autoantibodies. The effector functions of these PDC-E2(159-167)-specific CD8(+) cytotoxic T lymphocytes (CTLs) are not well understood. We have taken advantage of tetramer technology and report herein that there is tenfold increase in the frequency of PDC-E2(159-167)-specific CTLs in the liver as compared with the blood in PBC. In addition, the precursor frequency of the CTLs in blood was significantly higher in early-stage PBC. Of interest was the fact that, upon stimulation with the peptide, the response of PDC-E2(159-167) tetramer-positive cells is heterogeneous with respect to IFN-gamma synthesis. These data, we believe for the first time, document the enrichment of autoantigen-specific CD8(+) T cells in the PBC liver, suggesting that CD8(+) T cells play a significant role in the immunopathogenesis of PBC.