Genetic deletion of interleukin-15 is not associated with major structural changes following experimental post-traumatic knee osteoarthritis in rats

Post-traumatic Osteoarthritis (PTOA) is a degenerative joint disease, leading to articular cartilage breakdown, osteophyte formation, and synovitis, caused by an initial joint trauma. Pro-inflammatory cytokines increase catabolic activity and may perpetuate inflammation following joint trauma. Interleukin-15 (IL-15), a pro-inflammatory cytokine, is increased in OA patients, although its roles in OA pathophysiology are not well characterized. IL-15 levels appear to correlate to self-reported pain levels, and polymorphisms in the IL-15 receptor alpha gene correlate to a 1.5-fold increase in OA symptoms. This could be due to IL-15 effects on the activity of proteinases, such as matrix metalloproteinases (MMP) -1, -3, and -7. Here we utilized Il15 deficient rats to examine the role of IL-15 in PTOA pathogenesis in an injury-induced model of OA. OA was surgically induced in Il15 deficient rats and control wild-type rats to compare PTOA progression. Semi-quantitative scoring of the articular cartilage, subchondral bone, osteophyte size, and synovium was performed by two blinded observers. Analyses of articular cartilage damage, subchondral bone damage, and osteophyte formation revealed no significant difference between Il15 deficient rats and wild-type rats following PTOA-induction. Similarly, synovitis scoring across 6 parameters found no significant difference between genetic variants. Overall, IL-15 does not appear to play a key role in the development of structural changes in this surgically-induced rat model of PTOA.