Bactericidal/permeability increasing protein (BPI) is a leukocyte product exerting antibacterial activity. Its production may be stimulated by cytokines, mainly Tumor Necrosis Factor (TNF) alpha. We studied BPI in the synovial fluid (SF) of psoriatic arthritis (PsA), a disease suspected to be influenced by infectious agents.

The levels of BPI and various indices of SF inflammation, including cytokines and its receptors, were determined in the SF of 18 patients with PsA and compared with those of 12 patients with rheumatoid arthritis (RA) and 9 with osteoarthritis (OA).

The lowest SF levels of BPI were found in PsA (145.3 +/- 97.3 ng/ml), significantly lower than in RA (307.7 +/- 42.8 ng/ml, p = 0.0001) and similar to those in OA (151.1 +/- 52.4 ng/ml). Furthermore, only in PsA, and not in the RA and OA subgroups, correlations were observed between BPI and the indices considered, including TNF alpha (r = 0.746, p = 0.0004).

Due to its relationship with local inflammation, SF BPI may play a role in the pathogenesis of arthropathies, in particular PsA.