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Background There are few reports of a biological role for glycosyltransferases in the infiltration of osteoarthritic synovitis. The aim of this research was to investigate the expression and cellular location of β-1,4-galactosyltransferase Ⅰ (β-1,4-GaIT-Ⅰ) in a surgically-induced rat model of knee osteoarthritis (OA), and explore the role of β-1,4-GalT-Ⅰ in the pathogenesis of OA.Methods Male Sprague-Dawley rats were randomly divided into three groups: OA group, sham group and normal group. The model of OA was established in the right knees of rats by anterior cruciate ligament transaction (ACLT) with partial medial meniscectomy. Fibroblast-like synoviocytes (FLSs) obtained from normal rat synovial tissue were cultured.The expression of β-1,4-GalT-Ⅰ mRNA in the synovial tissue, articular cartilage and FLSs treated with tumor necrosis factor-α (TNF-α) were assayed by real-time PCR. West-blotting and immunohistochemisty were used to observe the expression of β-1,4-GalT-Ⅰ at the protein level. Double immunofluorescent staining was used to define the location of the β-1,4-GalT-Ⅰ with macrophage-like synoviocytes, FLSs, neutrophils, and TNF-α in the OA synovium. The alteration of TNF-α in FLSs which were treated with lipopolysaccharide (LPS) and β-1,4-GalT-Ⅰ-Ab were detected by enzyme-linked immunosorbent assay (ELISA).Results The mRNA and protein expression of β-1,4-GalT-Ⅰ increased in synovial tissue of the OA group compared with the normal and sham groups at two and four weeks after the surgery, however, no significant difference appeared in the articular cartilage. Immunohistochemistry also indicated that the β-1,4-GalT-Ⅰ expression in OA synovium at four weeks after surgery increased sharply compared with the control group. β-1,4-GalT-Ⅰ co-localized with macrophage-like synoviocytes, FLSa, neutrophils and TNF-α in rat OA synovitis. Moreover, in vitro β-1,4-GalT-Ⅰ mRNA in FLSs was affected in a dose- and time-dependent manner in response to TNF-α stimulation. ELISA revealed that the expression of TNF-α was attenuated in FLSs in vitro when treated with anti β-1,4-GalT-Ⅰ antibody.Conclusion β-1,4-GalT-Ⅰ may play an important role in the inflammation process of rat OA synovial tissue which would provide the foundation for further researching into the concrete mechanism of β-1,4-GalT-Ⅰ in OA synovitis.