Comprehensive Phenotyping of Circulating T and B Cell Subsets in Patients with Ankylosing Spondylitis Associated with Crohn’s Disease

Background: Ankylosing spondylitis (AS) associated with Crohn’s disease (CD) is a nosological form of spondyloarthropathies with a low population prevalence. The pathogenesis of this disease is not fully understood, and there are no precise differential diagnostic methods to distinguish AS associated with CD from AS and CD separately in the early stages of the disease. The main objective for this study is to define lymphocyte-mediated immunity in patients with AS associated with CD. Methods: For the pilot study, we recruited 4 groups: CD (n=16), AS+CD (n=13), AS (n=13) and healthy controls (HC, n=26). Immune phenotyping of peripheral blood lymphocytes via flow cytometry. Results: In the AS+CD group, circulating regulatory T cells (Treg) levels were increased compared to the other groups. The frequency of CD73+ Tregs within the effector memory (EM) compartment was also elevated in the AS+CD group relative to the AS and CD groups alone. At the same time, the EM Tcyt and EM Th populations were lower in the AS+CD group compared to the CD group. Tfh17 levels were lower in the AS+CD group than in the AS group and showed a positive correlation with Bm5 and switched memory B cells. Additionally, Tfh17 and switched memory B cells correlated negatively with acute-phase markers, whereas Tfh2 correlated positively with the BASDAI activity index. Conclusions: In patients with AS associated with CD, exhaustion of the regulatory compartment of adaptive immunity is seen, whereas the humoral component appears oriented towards resolving the inflammatory responses.