title: Co-culture of synovial fibroblasts and differentiated U937 cells is sufficient for high interleukin-6 but not interleukin-1beta or tumour necrosis factor-alpha release.
abstract: Inflamed synovium is characterized by high concentrations of cytokines [interleukin (IL)-6, IL-1beta and tumour necrosis factor (TNF)-alpha] and the abundant presence of infiltrated monocytes, many of which are found adjacent to the resident fibroblast-like synoviocytes. We have used a co-culture of fibroblast-like synoviocytes and differentiated U937 cells to study IL-6, IL-1beta and TNF-alpha release. After a 3 day co-culture, 35% of the U937 cells had adhered and were fully differentiated towards monocytes, as determined by expression of p47phox, CD14, MSE-1, Mac-1, collagenase and NADPH oxidase activity. IL-6 release from fibroblast-like synoviocytes was induced 4-fold by co-culture with differentiated U937 cells. However, co-culture of differentiated U937 cells with fibroblast-like synoviocytes failed to release detectable levels of IL-1beta and TNF-alpha from the U937 cells. Addition of synovial fluid further increased IL-6 release, but again had no effect on IL-1beta or TNF-alpha, although U937 cells differentiated by phorbol ester were able to release these two cytokines and, in the case of the co-culture, mRNAs for both cytokines were highly expressed in the U937 cells. We postulate that the influx of monocytes into the synovium is instrumental in the elevation of IL-6 levels, but this is not sufficient to explain high levels of IL-1beta or TNF-alpha.
authors.affiliation: Department of Dermatology, St Bartholomew's and the Royal London Hospital, School of Medicine and Dentistry.
authors.forename: V
authors.initials: V
authors.lastname: Chen
authors.forename: D
authors.initials: D
authors.lastname: Croft
authors.forename: P
authors.initials: P
authors.lastname: Purkis
authors.forename: I M
authors.initials: IM
authors.lastname: Kramer
mesh_terms: D000943:Antigens, Differentiation / Q000378:metabolism; D001172:Arthritis, Rheumatoid / Q000378:metabolism*; D002452:Cell Count; D002454:Cell Differentiation; D018920:Coculture Techniques; D017931:DNA Primers / Q000737:chemistry; D005347:Fibroblasts / Q000378:metabolism; D005434:Flow Cytometry; D006801:Humans; D007375:Interleukin-1 / Q000235:genetics / Q000378:metabolism*; D015850:Interleukin-6 / Q000235:genetics / Q000378:metabolism*; D009000:Monocytes / Q000737:chemistry / Q000378:metabolism*; D012333:RNA, Messenger / Q000096:biosynthesis; D012867:Skin / Q000166:cytology; D013582:Synovial Fluid / Q000378:metabolism; D013583:Synovial Membrane / Q000166:cytology / Q000378:metabolism*; D014407:Tumor Cells, Cultured; D014409:Tumor Necrosis Factor-alpha / Q000235:genetics / Q000378:metabolism*
chemical_list: D000943:Antigens, Differentiation; D017931:DNA Primers; D007375:Interleukin-1; D015850:Interleukin-6; D012333:RNA, Messenger; D014409:Tumor Necrosis Factor-alpha