Objective: To determine whether synovial expression of triggering receptor expressed on myeloid cells-1 (TREM-1) is up-regulated in patients with distinct types of inflammatory or non-inflammatory arthritis.
Methods: Synovial fluid (SF) samples were analyzed for levels of soluble TREM-1 (sTREM-1, n = 132), tumor necrosis factor α (TNFα, n = 78), and leukocyte TREM 1 mRNA (n = 48). Synovial tissue from 4 rheumatoid arthritis (RA) patients, 2 patients with Crohn’s associated arthritis, 1 patient with ankylosing spondylitis (AS), and 1 patient with osteoarthritis (OA) were examined for TREM-1 expression by immunohistology, and 3 of the RA samples were also analyzed by Western blotting.
Results: SF sTREM-1 levels in septic arthritis and RA were similar to each other and were each greater than those in gouty arthritis, non-septic/non-RA inflammatory arthritis, and non-inflammatory arthritis. SF TNFα and sTREM-1 levels correlated with each other, and sTREM-1 and leukocyte TREM-1 mRNA levels each correlated with SF leukocyte counts. TREM-1 in RA was expressed in situ in synovial tissue by cells of myelomonocytic lineage but was not detectably expressed in control OA synovial tissue.
Conclusions: Synovial TREM-1 expression is increased in septic arthritis and RA. In patients with acute inflammatory arthritis, elevated SF sTREM 1 levels may point the clinician to a diagnosis of septic arthritis or RA. In RA patients, targeting TREM-1 may have therapeutic benefits by reducing local proinflammatory cytokine and chemokine release.