Interleukin-8 mRNA expression in synovial fluid of canine stifle joints with osteoarthritis

The objective of this study was to examine and compare the presence of interleukin (IL)-8 mRNA in canine stifle osteoarthritis (OA) differing in etiopathogenesis. Synovial fluid (SF) samples were collected from 24 clinically normal stifle joints and 46 diseased stifle joints (32 stifle joints with cranial cruciate ligament rupture (CCLR), 2 joints with CCLR and patella luxation (PL), 7 joints with medial PL and 5 joints with primary OA). The samples were centrifuged to collect synovial fluid cells for RNA extraction. Reverse transcription polymerase chain reaction (RT-PCR) was performed to obtain cDNA from all samples. Canine IL-8 mRNA expression was determined using real time PCR. Synovial fluid glass smears were made of all samples and coloured with H&E for differential cell counts. All stifle joints were radiographed and graded for the severity of OA. Sixty-one percent (28/46) of the samples from canine stifle OA had IL-8 mRNA expression in contrast to 4% (1/24) in the control stifle joints. This difference in prevalence is highly significant. There were no statistically significant pairwise differences among the mean ranks of the various OA groups for the absolute amount of IL-8 mRNA expression. Neither was there a link between the severity of OA (determined by radiographic evaluation) and the presence of IL-8 in the SF nor any significant difference in the absolute amount of IL-8 between the different OA grades. No statistical difference was found in differential cell counts between IL-8-positive and -negative SF samples. IL-8 cannot be used as a specific joint disease marker since IL-8 expression is found in OA differing in etiopathogenesis. It might, however, relate to the ongoing inflammation within the joint.