Tissue Levels of Leukemia Inhibitory Factor Vary by Osteoarthritis Grade

The objective of this study was to observe the expression of leukemia inhibitory factor (LIF) in animals and in different clinical grades of patient osteoarthritic tissues. Thirty-five rabbits were used in a Colombo model of experimental osteoarthritis (OA). Five rabbits each were sacrificed on postoperative days 3, 7, 14, 28, 42, 56, and 84. Immunohistochemistry analysis for LIF expression and distribution in the cartilage and synovium of animals was performed at these times. Sixty-seven samples of human articular tissue were obtained from patients with different grades of OA according to symptoms and radiographic inspection. The mRNA expression of LIF was determined by reverse transcription polymerase chain reaction, and LIF protein was determined by enzyme-linked immunosorbent assay (ELISA). The results showed a slight expression of LIF in normal cartilage tissue but less in synovium tissue; however, the expression of LIF was marked in synovial lining cells and superficial and middle-layer cartilage in animal OA (P<.05). Leukemia inhibitory factor mRNA was expressed at the highest level in moderate degrading subchondral bone, and LIF was expressed at the highest level in seriously degrading articular cartilage tissue. These results were similar to those found with ELISA. This study suggests that LIF in OA articular tissues varies by clinical symptoms and grade. It plays an important role in the pathogenesis of OA.