In a clinical study by Filardo15, leukocyte-rich PRP (L-PRP) resulted in a higher incidence of side effects in the treatment of osteoarthritis compared with pure PRP (P-PRP), which had a lower leukocyte concentration, possibly due to the fact that leukocytes in PRP may deliver pro-inflammatory cytokines, such as interleukin-1β (IL-1β) and tumor necrosis factor-α (TNF-α), at the site of injection, resulting in the production of destructive proteases that inhibit the formation and promote the degradation of extracellular matrix15, 16, 17. This evidence concerns the gene TNF and osteoarthritis.