Different expression of TNF-alpha receptors and prostaglandin E-2 production in normal and fibrotic lung fibroblasts - Potential implications for theevolution of the inflammatory process

Normal human lung fibroblasts downregulate the production of tumor necrosis factor (TNF)-alpha by activated monocytes through the production of prosta glandin E-2 (PGE(2)), contributing to the local control of the inflammatory process. In this study, we provide evidence that fibroblasts derived from diseased tissue, such as fibrotic lung fibroblasts, exhibit different funct ional features compared with normal cells, with particular regard to their modulatory role. Indeed, fibrotic fibroblasts (FF) spontaneously produced l ess PGE(2) (3,300 +/- 410 pg/ml) compared with normal fibroblasts (NF) (7,5 00 +/- 270 pg/ml) and, as a consequence, they showed a reduced ability to d ownregulate the production of TNF-alpha by lipopolysaccharide (LPS)activate d monocytes. The percentage of inhibition induced by normal cells on the pr oduction of TNF-alpha by LPS-activated monocytes was 61 +/- 5.9%, whereas t he inhibitory effect exerted by fibrotic cells was reduced to 32 +/- 4% (P < 0.01). We have also observed that the ability of TNF-alpha to induce PGE( 2) was impaired in FF and was related to a reduced expression of cyclooxyge nase 2. This was possibly due to the reduction of the expression of TNF rec eptors (TNFRs) in fibrotic cell lines compared with normal cell lines. Flow cytometry revealed that the mean fluorescence intensity (MFI) of both isof orms of TNFR was significantly lower in FF compared with NF. The MFI of TNF R1 was 3.55 +/- 0.12 for NF and 1.78 +/- 0.35 for FF (P < 0.001). The MFI o f TNFR2 was 1.95 +/- 0.27 for NF and 0.99 +/- 0.16 for FF (P < 0.01). The a nalysis of the effect of TNF-alpha on some functions associated with collag en metabolism in NF and FF showed an increase of the expression of the rece ptor for collagen type I (alpha(2)beta(1) integrin) in NF (42 +/- 10%) and an even larger increase in FF (102 +/- 23%) (P < 0.05). Interestingly, unli ke NF, TNF-alpha failed to increase matrix metalloproteinase 1 levels in FF and did not cause any growth inhibition in these cells. The reduced capabi lity of fibrotic cells to produce PGE(2) either spontaneously or after TNF- alpha treatment may lead to an unrestrained release of TNF-alpha from activ ated monocytes and, as a result of the reduced expression of TNFRs, to a di fferent response of these cells to TNF-alpha. These changes may be importan t in the evolution of the inflammatory process, potentially contributing to its transformation into a chronic and self-perpetuating process.