Interleukin 13 in synovial fluid and serum of patients with psoriatic arthritis

To compare the pattern of interleukin (IL) 13 production in synovial fluid (SF) and serum of patients with psoriatic arthritis (PsA) with that in patients with rheumatoid arthritis (RA) and osteoarthritis (OA), investigating its relation to the proinflammatory cytokine IL12.

SF and serum IL13 levels were determined in 35 patients with PsA, 36 with RA, and 15 with OA. The main clinical and laboratory variables, including number of painful and/or swollen joints, Ritchie index, morning stiffness, erythrocyte sedimentation rate, level of C reactive protein, level of rheumatoid factor, and SF analysis, were also evaluated.

SF IL13 levels were significantly higher in patients with PsA (p<0.02) or RA (p<0.012) than in patients with OA, with no significant difference between the former two. SF IL12 levels were significantly higher in patients with PsA (p<0.023) than in those with OA. Serum IL13 (p<0.0001) and IL12 (p<0.02) levels were lower in patients with PsA than in those affected by RA. Only patients with PsA had higher IL13 levels in SF than in serum (p<0.002). The IL13 SF/serum ratio was higher in the PsA group than in the group with RA (p<0.005) or OA (p<0.026). SF IL13 levels correlated with serum IL13 levels (p<0.0001) in RA and with SF IL12 levels (p<0.03) in PsA.

In PsA, there appears to be localised production of IL13, in balance with IL12, in the inflamed joints. The distinct IL13 secretion profiles in PsA, RA, and OA may be related to the clinical pictures, reflecting the different pathogenic mechanisms involved in inflammatory and degenerative joint diseases.