Background Ankylosing Spondylitis (AS), with poorly understood pathogenesis, is a chronic inflammatory rheumatic disease, and as a result of inflammation, morbidity and mortality may occur. Many cell types are involved in inflammatory process, and particularly antigen presentation is important. Monocytes are also one of the most important sources of antigen presenting cells, activated by inflammation and chemotactic stimulation, reach the inflammatory focus through the vessel wall and become macrophage, a cell type which has more highly phagocytic ability. There are two main monocyte populations in peripheral blood. First, forming a smaller population, less mature, has a lower volume and higher tumoricidal activity cells (CD14^+/CD16⁺), second and higher population, consist of more mature monocytes; this monocytes have a higher volume, and they get more actively involved in antibody dependent cellular cytotoxicity (CD14⁺/CD16^-). CCR2 is a chemokine expressed on monocytes, and in inflammatory condition they play an important role on extravasation and transmigration of monocytes.

Objectives The aim of this study is to evaluate phenotypes and determine the distribution according to disease activity of monocytes, important source of antigen presenting cells, in patients with AS.

Methods Patients classified as AS according to modified New York criteria and healthy controls were included. Patients on biologic treatment have an active infection, or known chronic diseases were excluded. Besides routine clinic laboratory evaluation, to determine subtypes and activation status of monocytes, flow cytometry analyzes were performed on peripheral blood. In multi- colored analyze CD14-FITC, CD16-PE and CCR2-PerCP were used. Monocyte percentages and monocyte subtype were determined. CCR2 expression on monocytes and on monocyte subtypes was studied.

Results The demographic characteristics of AS patients and controls were summarized on table. Inflammatory markers were found to be significantly higher in patients with AS. Apart from percentages of CD14⁺/CD16⁺ and CD14^+/CD16^- subtypes which were similar between two groups, CCR2 expression was detected significantly higher in AS patients in both subgroups. There was no difference between monocyte subgroups and CCR2 expressions when classified according to disease activity in patients with AS.

Conclusions In our study, compared to control group, CCR2 expression on monocyte subgroups was significantly higher independent from disease activity in patients with AS. We believe, this may contribute to the understanding of inflammatory process in AS patients.

Disclosure of Interest None declared