Background/Purpose:

 Idiopathic inflammatory myopathy is a rare chronic inflammatory disease that is associated with the presence of autoantibodies pointing to a contribution of adaptive immune responses to disease manifestation. One of the most frequent myositis-specific autoantibodies is raised against histidyl-tRNA synthetase (Jo1). This autoantibody can be detected in 20% of myositis patients and is associated with interstitial lung disease (ILD). ILD may precede myositis symptoms implicating that the autoimmune reaction may start in the lungs. The release of Jo1 and fragments thereof into the extracellular milieu is believed to trigger both activation of T cells by antigen-presenting cells and influx of CCR5 expressing cells e.g. dendritic cells and Th1 lymphocytes. So far, there is only limited knowledge about Jo1-reactive T cells in myositis patients.

Methods:

A candidate T cell epitope was predicted from the N-terminal part of the Jo-1 protein. In order to identify and characterize Jo1 antigen-specific Th cells, we stimulated peripheral blood (n=9) and BAL cells (n=3) of myositis patients with either recombinant Jo1 protein or the 13aa peptide covering the predicted epitope. Subsequently, CD3⁺CD4⁺T cells were analyzed for up-regulation of CD40L by flow cytometry at day 5. In addition, T cells were examined for effector functions by measuring expression of intracellular cytokines. Finally we compared the phenotype of T cells in blood and BAL (n=4) by staining for Th1 associated chemokine receptors.

Results:

Stimulation of cells from blood and BAL with Jo1 protein caused a high up-regulation of CD40L on CD3⁺CD4⁺ T cells. Thus, Jo1-specific CD4⁺T cells can be detected in both blood and BAL fluid of myositis patients. Upon activation, Jo1-specific T cells mainly show Th1 effector functions as evident by IFNg expression.

Stimulation of cells with the 13aa peptide corresponding to our novel candidate T cell epitope also resulted in a high up-regulation of CD40L.

Moreover, Jo1-reactive T cells are highly enriched in the BAL fluid. Those antigen-specific T cells have a highly pronounced Th1 phenotype as around 60% produce IFNg in response to antigen stimulation compared to only 10% IFNg responders in the corresponding blood samples. Interestingly, BAL T cells were all (100%) positive for CXCR3 and CCR5, two chemokine receptors specifically expressed on Th1 cells. In contrast, CD4⁺T cells derived from blood only showed 20% positivity for CCR5 and CXCR3 expression, respectively.

Conclusion:

 In this study, we were able to demonstrate presence of Jo1-reactive CD4⁺ T cells in inflammatory myopathies and thus provide evidence that those T cells do react with epitopes on this autoantigen. Jo1 reactive CD4⁺ T cells are also present in the lung and show here pronounced Th1 effector functions. Moreover, we were able to identify a novel T cell epitope of the histidyl-tRNA synthetase. This will open up new ways for studying disease mechanisms and might provide novel starting points for therapeutic intervention.

ACR Meeting Abstracts - https://acrabstracts.org/abstract/characterization-of-histidyl-trna-synthetase-specific-th-cell-response-in-blood-and-broncheoalveolar-lavage-bal-of-myositis-patients/