Serum and synovial fluid interleukin-15 level in rheumatoid arthritis

Abstract EN

In a trial to a assess the value of interleukin-15 (IL-15) as an important cytokine implicated in the pathogenesis of rheumatoid arthritis (RA), and its correlation with disease activity, its level was measured in sera and synovial fluids of 44 RA patients, 22 were in the active stage of the disease (with synovial effusion} and the other 22 were in remission, (12 in the subacute and 10 in the chronic stage of the disease) out of all patients, 30 were seropositive and 14 were seronegative for rheumatoidfactor (RF).

Values of serum IL-15 of RA patients were compared with those of 12 apparently healthy age and sex matched controls, while values of synovial fluid (SF) IL-15 in the active RA patients were compared with IL-15 levels in SF of 12 osteoarthritic patients (OA) as a control group.

The study revealed undetectable serum IL-15 levels in normal controls and 15 RA patients [5 in the active stage and 10 in remission (7 in the chonic and 3 in the subacute stage].

In comparing RA patient groups, it was found that serum IL-15 was significantly higher in the active group than in the remission group (P<0.05) and in the subacute than in the chronic stage ofRA(P<0.01).

In paired samples (n=22) of sera and SF from RA patients, IL-15 levels were higher in the SF than in sera (p<0.001), in addition, the SF levels of IL-15 in RA patients significantly exceeded those present in OA (P<0.001).

Serum IL-15 was found to be positively correlated with synovial fluid IL-15 in active RA patients (r=0.703, p<0.001).

Serum 1L-15 was higher in RA patients with positive rheumatoid factor (p<0.05), also a significant positive correlation was detected between synovial fluid IL-15 and rheumatoid factor inactive RA patients (r=0.719, p<0.01).

C-reacttve protein (CRP) was positively correlated with synovial fluid IL-15 in the active group ofRA (r-0.501, p<0.05).

There was a significant positive correlation between serum and synovial fluid IL-15 in active RA on one hand and ESR on the other hand (r=0.623,p<0.01 andr~0.452, p<0.05 respectively), in the same patient group, serum and synovial fluid IL-15 were positively correlated with all clinical parameters of disease activity including: duration of morning stiffness (r=0.464, p<0.05 andr=0.656, p<0.001 respectively), number of swollen joints(r=0.761, P<0.001 and r=0.576, P<0.01 respectively), and number of tender joints (r=0.897, P<0.001 and r=0.611, P<0.01 respectively).

No correlation could be detected between IL-15 levels whether in the serum or the synovial fluid and duration of the disease in RA.

In conclusion a higher concentration cfIL-15 is found mainly in RA synovial fluid.

This locally produced cytokine can contribute to the pathogenesis of RA, also 1L-15 can be used as a parameter of disease activity, in RA.