CD74 is a T cell antigen in spondyloarthritis.

Objective Spondyloarthritis (SpA) is a chronic inflammatory disease of unknown aetiology. Previously, we identified autoantibodies against CD74 in sera of SpA patients. The aim of this study was to evaluate CD74 as a T cell antigen in SpA. Methods Recombinant CD74 protein and a panel of selected peptides representing its amino acid residues were examined for their capability to stimulate peripheral blood mononuclear cells from patients with SpA. In particular, cytokine production by CD4(+) T cells was evaluated with flow cytometric detection of intracellular TNF-alpha, IFN gamma, TGF beta and IL-17A. Patients' sera were tested for antibodies against CD74 using ELISA. Samples from patients with rheumatoid arthritis and healthy blood donors were similarly tested as controls. Results Significantly more CD4(+) T cells from SpA patients produced TNF-alpha, IFN gamma and IL-17A in response to recombinant CD74 than patients with rheumatoid arthritis or healthy blood donors. Among evaluated epitopes, the most promiscuous one lies within the peptide of the amino acid residues 142-185, which appeared more immunogenic. Further, the proportion of cytokine producing CD4(+) T cells was significantly higher among SpA patients with autoantibodies against CD74. Conclusion CD74 is a T cell antigen in SpA, eliciting Th1 and Th17 responses, which may be relevant in disease pathogenesis. Recognition of the highly immunogenic amino acid residues of CD74 may contribute to our understanding of autoimmune responses of T helper cells in SpA.