Identification and characterization of SmD183–119‐reactive T cells that provide T cell help for pathogenic anti–double‐stranded DNA antibodies

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Abstract
Objective The C‐terminal peptide of amino acids 83–119 of the SmD1 protein is a target of the autoimmune response in human and murine lupus. This study was undertaken to test the hypothesis that SmD183–119‐reactive T cells play a crucial role in the generation of pathogenic anti–double‐stranded DNA (anti‐dsDNA) antibodies. Methods Splenic or lymph node T cells derived from unmanipulated as well as SmD183–119‐immunized NZB/NZW mice were analyzed in vitro by enzyme‐linked immunospot (ELISpot) assay to determine T cell help for anti‐dsDNA generation induced by the SmD183–119 peptide. Cytokines expressed by these T cells were measured by ELISpot assay, enzyme‐linked immunosorbent assay, and flow cytometry. SmD183–119‐ and ovalbumin‐specific T cell lines were generated and characterized. Results The SmD183–119 peptide, but not the control peptides, significantly increased the in vitro generation of anti‐dsDNA antibodies in cultures from unmanipulated NZB/NZW mice. Interferon‐γ (IFNγ), interleukin‐2 (IL‐2), IL‐4, transforming growth factor β, and IL‐10 production increased in response to the peptide in young mice; only IFNγ and IL‐2 were increased in older, diseased mice. Activation of SmD183–119‐reactive T cells by immunization of NZB/NZW mice resulted in elevated anti‐dsDNA synthesis and, later, increased antibodies to SmD183–119. Most cells in SmD183–119‐specific CD4+ T cell lines helping both antibodies had increased intracellular expression of IFNγ, and most expressed both IFNγ and IL‐4. Conclusion The SmD183–119 peptide plays an important role in generating T cell help for autoantibodies, including anti‐dsDNA, and activates different subsets of T cells as defined by distinct cytokine expression. This peptide is an interesting target structure for the modulation of autoreactive T cells, and its characterization may contribute to our understanding of the role of autoantigen‐reactive T cells in the pathogenesis of SLE.