Identification and characterization of antigen-specific CD4⁺ T cells targeting renally expressed antigens in human lupus nephritis with two independent methods

In the search for anti-renal autoreactivity in human lupus nephritis, we stimulated blood-derived CD4⁺ T cells from patients with systemic lupus erythematosus with various kidney lysates. Although only minor responses were detectable, these experiments led to the development of a search algorithm that combined autoantibody association with human lupus nephritis and target gene expression in inflamed kidneys. Applying this algorithm, five potential T cell antigens were identified. Blood-derived CD4⁺ T cells were then stimulated with these antigens. The cells were magnetically enriched prior to measurement with flow cytometry to facilitate the detection of very rare autoantigen-specific cells. The detected responses were dominated by IFN-γ-producing CD4⁺ T cells. Additionally, IL-10-producing CD4⁺ T cells were found. In a next step, T cell reactivity to each single antigen was independently evaluated with T cell libraries and [³H]-thymidine incorporation assays. Here, Vimentin and Annexin A2 were identified as the main T cell targets. Finally, Vimentin reactive T cells were also found in the urine of three patients with active disease. Overall, our experiments show that antigen-specific CD4⁺ T cells targeting renally expressed antigens arise in human lupus nephritis and correlate with disease activity and are mainly of the Th1 subset.