Susceptibility to ankylosing spondylitis but not disease outcome is influenced by the level of HLA-B27 expression, which shows moderate variability over time

Objective: Previous reports have highlighted the relevance of HLA-B27 expression in the pathogenesis of ankylosing spondylitis (AS). The aim of the current study was to estimate the level of HLA-B27 expression on the cell surface of ex vivo monocytes and lymphocytes by a quantitative method and to correlate this with AS disease susceptibility, disease clinical indexes, and the occurrence of acute anterior uveitis (AAU).Method: We recruited 32 B27-positive patients with AS and 32 B27-positive healthy normal controls (NCs) for evaluation at different time points. The expression of HLA-B27 molecules was quantified by flow cytometry on ex vivo peripheral blood mononuclear cells (PBMCs). Patients were also evaluated by scores on the Bath AS disease activity (BASDAI), functional (BASFI), and metrology (BASMI) indexes.Results: The expression of HLA-B27 molecules was significantly higher in patients with AS than in B27-matched controls in the case of both monocytes [219K (IQR 174K–308K) vs. 137K (IQR 96K–170K), p...