Cytokine production in the infrapatellar fat pad: another source of cytokines in knee synovial fluids.

BACKGROUND: Recent studies have shown that adipose tissue is an endocrine organ that releases various cytokines. OBJECTIVE: To investigate the production of growth factors and proinflammatory cytokines in infrapatellar fat pad specimens. METHODS: Infrapatellar fat pad tissues were obtained from patients during knee surgery. Protein levels of basic fibroblast growth factor (bFGF), vascular endothelial growth factor (VEGF), tumour necrosis factor (TNF)alpha, and interleukin (IL)6 in homogenised tissues were measured by an enzyme immunoassay. Gene expressions for those cytokines were examined by reverse transcription-polymerase chain reaction (RT-PCR). Localisation of bFGF and VEGF was evaluated by immunohistochemistry and in situ hybridisation. RESULTS: Infrapatellar fat pads were found to contain various protein levels of bFGF, VEGF, TNF alpha, and IL6. Further, gene expressions for these cytokines were detected by RT-PCR. Immunohistochemistry and in situ hybridisation showed that the expressions of both bFGF and VEGF were localised in immature adipocytes, interstitial undifferentiated mesenchymal cells, and vascular endothelial cells. CONCLUSION: The production of bFGF, VEGF, TNF alpha, and IL6 in the infrapatellar fat pad was demonstrated. Although synovial cells and articular chondrocytes are thought to be primary sources of cytokines found in knee synovial fluids, the results suggest that they may also originate from this fat pad.