Chondrocyte expression of IL-7 receptors. (a) Chondrocytes isolated from normal cartilage (n = 1) were incubated with a fluorescently labeled recombinant IL-7 to demonstrate binding of IL-7 to the cell surface. Labeled cells were examined by flow cytometry. The peak that is shaded purple with the black line shows cells stained with IL-7, the peak with the pink line shows blocking antibody negative control, and the peak with the green line shows cells stained with the biotin negative control. (b) Chondrocytes isolated from normal cartilage were incubated with a fluorescently labeled recombinant IL-7 as above. Labeled cells were examined by confocal microscopy. IL-7 staining is shown in green. Top left is the green channel, top right is differential intermittent contrast, and bottom left is the merged image. Chondrocytes from eight different donors showed similar results. (c) Pooled RNA isolated from 10 different sets of cultured chondrocytes was subjected to reverse transcription and real-time PCR with an IL-7 receptor primer set. An amplification plot is shown to demonstrate positive signal. Amplified chondrocyte cDNA in triplicate is shown with the blue lines. Negative control with no reverse transcription of RNA before real-time PCR is shown with a red line. Negative control with no cDNA is shown with the black line.