Interleukin 6 as a marker of mesangial cell proliferative activity
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Background. The role of Interleukin 6 (IL-6) in the pathogenesis of mesangial proliferative glomerulonephritis has been controversial. To test the hypothesis that glomerular mesangial cell (GMC)-derived IL-6 may not be a mitogen for GMCs, but, rather, a factor that reflects GMC proliferative activity, we investigated how the culture condition; namely, cell confluency, affected IL-6 production in human cultured GMCs.
Methods. IL-6 in the culture supernatant was measured by enzyme-linked immunoassay (ELISA). The expression of IL-6, IL-6 receptor (IL-6R), and proliferating cell nuclear antigen (PCNA) mRNA in GMCs was examined by reverse transcriptase polymerase chain reaction (RT-PCR). The effects of human recombinant IL-6 (rIL-6) on the proliferation of GMCs and an IL-6 dependent cell line, B9 cells, were evaluated by a colorimetric assay.
Results. The IL-6 ELISA study revealed that subconfluent GMCs secreted more IL-6 than confluent GMCs (12.9 ± 2.9 pg/104 cells versus 4.05 ± 0.2 pg/104 cells; P < 0.01). In the RT-PCR, the mRNA expression of both IL-6 and PCNA was upregulated in subconfluent GMCs as compared with confluent GMCs. An approximately four-fold increase in IL-6 mRNA expression and a two-fold increase in PCNA mRNA expression were shown. IL-6R mRNA expression was demonstrated in GMCs by RT-PCR. However, recombinant human IL-6, which stimulated the growth of B9 cells in a dose-dependent fashion, did not induce GMC proliferation.
Conclusions. GMC-derived IL-6 may have significance as a marker of GMC proliferative activity, although GMC-derived IL-6 per se does not act as an autocrine growth factor for GMCs.
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