Background Ankylosing spondylitis (AS) is a chronic inflammatory disease, of unknown aetiology, characterized by pathological new born formation. Yet, the relevance of immune system in the activation of inflammatory and osteoproliferative pathways in this disease is still unknown.

Objectives 1) To analyze the profile of inflammation, oxidative status and bone turnover in plasma and leukocyte subsets, as well as the endothelial function in AS patients. 2) To evaluate the relationship among those biomarkers and their correlation with disease activity.

Methods Thirty patients with AS and 30 healthy donors were included in the study. Disease function and activity status were analyzed using the BASFI and BASDAI indexes, respectively. Endothelial function was determined by the post occlusive hyperaemia test using Laser-Doppler. Several biomarkers of oxidative stress, inflammation, thrombosis and bone turnover were analyzed in leukocyte subsets (lymphocytes, neutrophils and monocyte subsets: classic or MON1:CD14+/CD16-; intermediate or MON2:CD14+/CD16+; non-classic or MON3:CD14dim/CD16+) by RT-PCR and flow cytometry. Antioxidant enzyme activities, nitric oxide (NO) and total antioxidant capacity (TAC) of plasma were measured by specific kits.

Results Compared to healthy donors, a significant alteration of the endothelial function was observed in AS patients. Several inflammatory and osteogenic markers were differentially modified in the different immune cell subsets. Neutrophils showed an increase in the inflammatory markers TNFa, IL6, ERAP1 and IL10, whereas lymphocytes displayed increased TNFa, IL-2 e IKK. The monocyte analysis demonstrated a reduction in MON1 percentage, along with an increase in MON2 and MON3 percentage. MON1 monocytes showed a specific increase of IL1b e IL6, whereas MON2+MON3 increased IL10, IL23, MCP1, MIP1a, ERAP1, TF e IKK. The osteogenic markers significantly altered in neutrophils were TGFb, ALP, DKK1 y Runx2. Non-significant changes were observed in lymphocytes, whereas MON1 showed elevated BMP2 and OPG levels. Oxidative stress analysis demonstrated an increase in catalase activity, peroxides and percentage of cells with depolarized mitochondria in all leukocyte subsets, along with a reduction of plasma NO and TAC.

Correlation and association studies showed that endothelial dysfunction and oxidative damage were associated with evolution time of the disease and BASFI. Mitochondrial dysfunction was correlated with an increase in osteogenic markers. Increase in inflammatory markers was associated with endothelial dysfunction, oxidative status and BASDAI index.

Conclusions 1) AS patients show an endothelial dysfunction directly associated with the inflammatory profile and disease progression. 2) Circulating leukocyte subsets in AS patients seem to play a differential role in the inflammatory and bone turnover processes, so that neutrophils and classic monocytes seem to mediate both processes whereas lymphocytes and non-classic monocytes seem to be more associated with the inflammatory process. 3) The oxidative stress and, particularly, the mitochondrial dysfunction, may act as a key mediator in the inflammation and new born formation processes present in AS patients.

Acknowledgements Funded by JA PI-0314-2012, SER

Disclosure of Interest None declared