Critical Requirement for Professional APCs in Eliciting T Cell Responses to Novel Fragments of Histidyl-tRNA Synthetase (Jo-1) in Jo-1 Antibody-Positive Polymyositis

Abstract

Polymyositis (PM) is an autoimmune muscle disease characterized by oligoclonal T cell infiltrates mediating myocytotoxicity. Although antigenic triggers for this process remain undefined, clinically homogeneous subsets of PM patients are characterized by autoantibodies directed against nuclear and cytoplasmic Ags that include histidyl-tRNA synthetase (Jo-1). Available evidence suggests that formation of anti-Jo-1 autoantibodies is Ag-driven and therefore dependent on CD4+ T cells that may also direct cytolytic CD8+ T cells involved in myocyte destruction. To assess peripheral blood T cell responses to Jo-1, we first subcloned full-length human Jo-1 as well as novel fragments of Jo-1 into the maltose-binding protein expression vector pMALc2. Expressed proteins were then used in standard proliferation assays with either PBMC or autologous DCs as sources of APCs. Although PBMC-derived APCs and DCs both supported peripheral blood T cell proliferation when primed with full-length human Jo-1, only DCs promoted proliferative responses to a unique amino-terminal fragment of Jo-1. mAb blockade of different HLA Ags revealed that these responses were MHC class II dependent. Therefore, for the first time, these studies demonstrate anti-Jo-1 T cell responses in Jo-1 Ab-positive PM patients as well as in healthy control subjects. More importantly, this work underscores the critical importance of APC type in dictating T cell responses to a novel antigenic fragment of Jo-1.

Species-specific immune responses generated by histidyl-tRNA synthetase immunization are associated with muscle and lung inflammation

“…Consistent with this hypothesis, we have previously demonstrated Jo-1-specific T cells in the peripheral blood of Jo-1 antibody-positive patients [14]. However, because T cells targeting Jo-1 can also be found in individuals without disease [14], a direct link between such T cells and myocytotoxicity is currently lacking.…”

“…Expressed proteins were purified with amylose resin per the manufacturer's protocol (New England Biolabs, Ipswich, MA), filter sterilized, and then subjected to additional column purification for endotoxin removal (Profos AG, Regensburg, Germany) prior to use in proliferation assays. As previously described [14], full length versions of Jo-1 were cleaved with Factor Xa (New England Biolabs, Ipswich, MA) to release the MBP moiety and further purified using ion exchange chromatography.…”

“…However, because T cells targeting Jo-1 can also be found in individuals without disease [14], a direct link between such T cells and myocytotoxicity is currently lacking. Establishing appropriate in vitro and in vivo models to analyze Jo-1-specific T cell clones is therefore necessary to determine whether antibodies targeting Jo-1 merely represent markers of disease or reflect pathogenic, antigen-specific T cell responses.…”

Anti–Jo‐1 antibody levels correlate with disease activity in idiopathic inflammatory myopathy

“…While histopathologic and immunohistochemical studies support T cell-mediated tissue damage rather than humoral mechanisms for myocytotoxicity (19)(20)(21), the association of class-switched anti-Jo-1 antibody with muscular as well as extramuscular disease activity suggests that underlying Jo-1-specific T cells fuel both anti-Jo-1 antibody formation and cell-mediated immune responses. In fact, we have previously demonstrated the existence of Jo-1-specific T cells in anti-Jo-1 antibodypositive patients (22). Such T cells also exist in the repertoire of nondiseased control subjects, but the absence of anti-Jo-1 antibody in these individuals indicates that Jo-1-specific T cells have not been activated in vivo.…”

The Antisynthetase Syndrome

“…Whether similar mechanisms are operative in the lung is not known, but it has been suggested that HRS adopts a more immunogenic conformation in the lung than in blood cells (28). Previously, it was shown that T cells from the blood of both ASS patients and healthy individuals often recognized HRS (29). No data on T cell or B cell reactivities to HRS in inflamed muscle or lung exist, but CD4+ T cells from the bronchoalveolar lavage fluid of two anti-Jo-1+ ASS patients have been shown to contain the same T cell receptor gene family (30).…”