Altered Repertoire Diversity and Disease-Associated Clonal Expansions Revealed by T Cell Receptor Immunosequencing in Ankylosing Spondylitis Patients

Objective Ankylosing spondylitis (AS) is a common spondyloarthropathy primarily affecting the axial skeleton and strongly associated withHLA-B*27carriage. Genetic evidence implicates both autoinflammatory processes and autoimmunity against anHLA-B*27-restricted autoantigen in immunopathology. In addition to articular symptoms, up to 70% ofASpatients present with concurrent bowel inflammation, suggesting that adverse interactions between a genetically primed host immune system and the gut microbiome contribute to the disease. Accordingly, this study aimed to characterize adaptive immune responses to antigenic stimuli inAS. Methods The peripheralCD4 andCD8 T cell receptor (TCR) repertoire was profiled inASpatients (n = 47) andHLA-B*27-matched healthy controls (n = 38). Repertoire diversity was estimated using the Normalized Shannon Diversity Entropy (NSDE) index, and univariate and multivariate statistical analyses were performed to characterizeAS-associated clonal signatures. Furthermore, T cell proliferation and cytokine production in response to immunogenic antigen exposure were investigated in vitro in peripheral blood mononuclear cells fromASpatients (n = 19) andHLA-B*27-matched healthy controls (n = 14). Results Based on theNSDEmeasure of sample diversity acrossCD4 andCD8 T cell repertoires,ASpatients showed increasedTCRdiversity compared to healthy controls (forCD4 T cells,P= 7.8 x 10(-6); forCD8 T cells,P= 9.3 x 10(-4)), which was attributed to a significant reduction in the magnitude of peripheral T cell expansions globally. Upon in vitro stimulation, fewer T cells fromASpatients than from healthy controls expressed interferon-gamma (forCD8 T cells,P= 0.03) and tumor necrosis factor (forCD4 T cells,P= 0.01; forCD8 T cells,P= 0.002). In addition, theCD8TCRsignature was altered inHLA-B*27+ASpatients compared to healthy controls, with significantly expanded Epstein-Barr virus-specific clonotypes (P= 0.03) and cytomegalovirus-specific clonotypes (P= 0.02).HLA-B*27+ AS patients also showed an increased incidence of public CD8 TCRs, representing identical clonotypes emerging in response to common antigen encounters, including homologous clonotypes matching those previously isolated from individuals with bacterial-induced reactive arthritis. Conclusion The dynamics of peripheral T cell responses in AS patients are altered, suggesting that differential antigen exposure and disrupted adaptive immunity are underlying features of the disease.