Connective tissue growth factor (CCN2) is a profibrotic factor acting downstream and independently of TGF-b to mediate renal fibrosis. Although inflammation is often involved in the initiation and/or progression of fibrosis, the role of inflammatory cytokines in regulation of glomerular CCN2 expression, cellular proliferation and extracellular matrix accumulation is unknown. We studied two such cytokines, TNF-a and IFN-g, for their effects on cultured mesangial cells in the presence or absence of TGF-b, as a model for progressive nephrofibrosis. Short-term treatment with TNF-a, like TGF-b, significantly increased secreted CCN2 per cell, but unlike TGF-b inhibited cellular replication. TNF-a combined with TGF-b further increased CCN2 secretion and mRNA levels and reduced proliferation. Surprisingly however, TNF-a treatment decreased baseline collagen type I protein and mRNA levels, and largely blocked their stimulation by TGF-b. Long-term treatment with TGF-b or TNF-a alone, no longer increased CCN2 protein levels. However, the combination synergistically increased CCN2. IFN-g had no effect on either CCN2 or collagen activity and produced a mild inhibition of TGF-b-induced collagen only at a high concentration (500 U/ml). In summary, we report a strong positive regulatory role for TNF-a, but not IFN-g, in CCN2 production and secretion, including that driven by TGF-b. The stimulation of CCN2 release by TNF-a, unlike TGF-b, is independent of cellular proliferation, and not linked to increased collagen type I. This suggests that the paradigm of TGF-b-driven CCN2 with subsequent collagen production may be overridden by an as yet undefined inhibitory mechanism acting either directly or indirectly on matrix metabolism.