title: Susceptibility to ankylosing spondylitis but not disease outcome is influenced by the level of HLA-B27 expression, which shows moderate variability over time.
abstract: 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).
  
  
  METHODS
  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 < 0.0001] and lymphocytes [82K (IQR 58K-118K) vs. 54K (IQR 44K-61K), p < 0.0001]; AS only vs. AS with AAU: p = 0.744 in monocytes and p = 0.701 in lymphocytes. Comparisons with metrology and functional indexes were also not significant (BASMI: r = 0.05, p = 0.77; BASFI: r = -0.09, p = 0.67). The overexpression of HLA-B27 molecules was stable after 1 week of follow-up. At 3 years follow-up, the variability was moderate and did not correlate with variations in disease activity (BASDAI: r = -0.01, p = 0.92 ns).
  
  
  CONCLUSIONS
  The level of HLA-B27 expression in PBMCs correlates with the susceptibility to AS but not with the disease outcome, nor with the occurrence of extra-articular manifestations such as AAU.
authors.affiliation: Rheumatology Unit, University of Cagliari, Cagliari, Italy. cauli@medicina.unica.it
authors.forename: A
authors.initials: A
authors.lastname: Cauli
authors.forename: G
authors.initials: G
authors.lastname: Dessole
authors.forename: A
authors.initials: A
authors.lastname: Vacca
authors.forename: G
authors.initials: G
authors.lastname: Porru
authors.forename: L
authors.initials: L
authors.lastname: Cappai
authors.forename: M
authors.initials: M
authors.lastname: Piga
authors.forename: P P
authors.initials: PP
authors.lastname: Bitti
authors.forename: M T
authors.initials: MT
authors.lastname: Fiorillo
authors.forename: R
authors.initials: R
authors.lastname: Sorrentino
authors.forename: C
authors.initials: C
authors.lastname: Carcassi
authors.forename: A
authors.initials: A
authors.lastname: Mathieu
mesh_terms: D000328:Adult; D000911:Antibodies, Monoclonal; D016022:Case-Control Studies; D004198:Disease Susceptibility; D005260:Female; D005434:Flow Cytometry; D005500:Follow-Up Studies; D015870:Gene Expression; D015796:HLA-B27 Antigen / Q000378:metabolism*; D006801:Humans; D008214:Lymphocytes / Q000276:immunology*; D008297:Male; D008875:Middle Aged; D009000:Monocytes / Q000276:immunology*; D012720:Severity of Illness Index; D013167:Spondylitis, Ankylosing / Q000276:immunology*
chemical_list: D000911:Antibodies, Monoclonal; D015796:HLA-B27 Antigen