Objectives: The aims of this study were to examine immune cell proportions in peripheral blood of patients with ankylosing spondylitis (AS) and to investigate relationships between immune cells, level of bone formation related molecules, and radiographic changes.
Methods: Forty-nine AS patients and 53 age- and sex-matched healthy controls (HCs) were enrolled in this study. Clinical parameters were extensively evaluated in the study subjects. CD4+ T-cells, CD8+ T-cells, CD56+ T-cells, natural killer cells, and natural killer T (NKT) cells in peripheral blood were measured by flow cytometry. Serum levels of Dickkopf-1 and bone morphogenic proteins were determined using enzyme linked immunosorbent assays. Modified Stokes AS spinal scores were used to assess radiographic changes.
Results: Patients were found to have a significantly higher percentages of CD56+T-cells than healthy controls (median 1.31% vs. 0.53%, p<0.001), whereas percentages of peripheral blood natural killer T (NKT) cell were lower in patients than in controls (median 0.07 % vs. 0.10%, p=0.010). Moreover, mean CD 56+T to NKT cell ratio was markedly higher in patients. Although no significant correlations were observed between the immune cell percentages and bone formation-related molecule levels, interestingly, patients with a higher CD56+T to NKT cell ratio at baseline were found to develop greater radiographic changes (r=0.79, p=0.007, age and disease duration adjusted) during 3 years of radiographic follow-up.
Conclusions: An altered T-cell compartment, particularly with respect to CD56+ T and NKT cells, was observed in AS patients and could contribute to radiographic changes in AS.