Arginase-1 and Mer Tyrosine Kinase Expression in Monocyte Populations in Patients with Axial Spondyloarthritis

Axial spondyloarthritis is characterized by activation of innate immune cells, which manifested in elevation of classical monocytes and predominance of the proinflammatory phenotype. However, the immunosuppressive potential of monocyte/macrophages remains practically unexplored. We evaluated the expression of Mer tyrosine kinase (MerTK) and arginase-1 (Arg1) in monocyte subsets in patients with axial spondyloarthritis, considering different clinical features. The expression of MerTK and Arg1 in intermediate and non-classical monocytes from patients with axial spondyloarthritis was reduced in comparison with the normal. The most pronounced decrease in monocyte expression of MerTK and Arg1 was associated with a more aggressive course of the disease (presence of coxitis, high disease activity, HLA-B27 positivity) and lack of response to conventional therapy. These data demonstrate an important role of MerTK and Arg1 in limiting myeloid-driven inflammation.