Cytokine mRNA repertoire of articular chondrocytes from arthritic patients, infants, and neonatal mice

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Abstract
Articular chondrocytes from nine arthritic patients, five infants, and Balb/c neonatal mice were analyzed for the presence of various cytokine mRNAs by a reverse transcriptase polymerase chain reaction (RT-PCR). Four cytokine mRNAs, interleukin (IL)-6, IL-8, IL-11, and macrophage colony stimulating factor (M-CSF), were detected in all human chondrocytes, regardless of source. IL-10, IL-12p35, and tumor necrosis factor alpha (TNF-α) transcripts were found in at least 12 of the 14 human samples. IL-13, granulocyte colony stimulating factor (G-CSF), granulocyte macrophage colony stimulating factor (GMCSF), and TNF-βmRNAs were found more predominantly in infant samples and in samples from patients with rheumatoid arthritis (RA) compared with samples from patients with osteoarthritis (OA). Another group of cytokine mRNAs, IL-1 (α, β), IL-4, IL-5, and IL-7, were only weakly expressed in some human samples. The cytokine transcripts that were not found were IL-2, IL-3, and interferon gamma (IFN-γ. Because of the large array of cytokine transcripts detected, human chondrocyte preparations were further purified by reacting them with a monoclonal antibody specific to chondrocyte differentiation antigen and subjecting them to fluorescent-activated cell sorting. A similar array of cytokines was found between the sorted and unsorted chondrocytes, although TNF-α, G-CSF, and GM-CSF transcripts appeared to be upregulated during the sorting process. Human chondrocytes that dedifferentiated into fibroblasts (a 40-day and a 77-day culture) no longer expressed mRNAs for IL-1, G-CSF, GM-CSF, and TNF-α, but all other cytokine mRNAs remained detectable. Although certain phenotypic characteristics were lost:, including reactivity to chondrocyte-specific monoclonal antibodies and morphological features, chondrocytes in long-term culture still expressed cytokine mRNAs. As expected, more consistent results were obtained when seven preparations of chondrocytes from neonatal Balb/c mice were examined using available cytokine primers. They contained IL-1, IL-5, IL-6, IL-7, IL-12, GM-CSF, M-CSF, transforming growth factor beta (TGF-β), TNF-α, and TNF-β mRNAs but lacked IL-2, IL-3, IL-4, IL-10, and IFN-γ mRNAs. Future experiments to define conditions by which these cytokine protein products are expressed are needed to help assess their roles in chondrocyte biology and in disease states.