Detection of TNF-β and TNF-β receptor expression in cultured human chondrocytes in vitro by immunofluorescence microscopy. Primary human chondrocytes were either left untreated (Co. (A) and (E): without primary antibody; basal-co.: (B)) and (F) with primary antibody) or treated for 1 hour with 1 ng/ml interleukin 1β (IL-1β) (C) and (G) or 5 ng/ml IL-1β (D) and (H). Immunolabeling was performed with primary antibodies for tumor necrosis factor β (TNF-β) (B) through (D) and TNF-β receptor (TNF-β-R) (E) through (H), followed by incubation with rhodamine-coupled secondary antibodies and counterstaining with 4′,6-diamidino-2-phenylindole to visualize cell nuclei. Images shown are representative of three different experiments. Original magnification, ×400; bar, 30 nm.