C. Platzer et al., UP-REGULATION OF MONOCYTIC IL-10 BY TUMOR-NECROSIS-FACTOR-ALPHA AND CAMP ELEVATING DRUGS, International immunology, 7(4), 1995, pp. 517-523
It is well established that endotoxin [lipopolysacharide (LPS)] induce
s pro-inflammatory cytokine production in monocytes, which is followed
by secretion of the anti-inflammatory cytokine, IL-10. IL-10 down-reg
ulates inflammatory response [tumor necrosis factor (TNF)-alpha, IL-1,
IL-6, IL-8] as well as IL-10 synthesis itself. We wondered whether pr
o-inflammatory cytokines such as TNF-alpha may be involved in the regu
lation of human IL-10 synthesis. TNF-alpha induced de novo IL-10 mRNA
expression in a dose-dependent manner but no IL-10 protein in human pe
ripheral blood mononuclear cells. Furthermore, LPS-induced IL-10 gene
and protein expression was significantly inhibited by neutralizing ant
i-TNF-alpha mAb. On the basis of these results, we conclude that TNF-a
lpha is involved in the up-regulation of its antagonist IL-10. Paradox
ically, drugs that effectively inhibit expression of TNF-alpha via the
elevation of intracellular cAMP level (iloprost, pentoxifylline, pros
taglandin E(2) and N6,2-O-dibutyryl cAMP) augmented the endotoxin-indu
ced IL-10 synthesis at both protein and mRNA levels. In order to provi
de a basis for the analysis of the transcriptional regulation of the h
uman IL-10 gene, we isolated a fragment of the human IL-10 gene contai
ning 1308 bp of the 5' non-coding sequence. It shows remarkable homolo
gy to the mouse IL-10 promoter in regions that have been associated wi
th transcriptional regulation, including a cAMP responsive element whi
ch could explain the cAMP-mediated effects. The lack of a NF-kappa B-l
ike binding site in the human sequence suggests a NF-kappa B-independe
nt mechanism of TNF-alpha-induced IL-10 gene activation. In summary, o
ur data demonstrate that TNF-alpha and cAMP elevating mediators, via i
nduction of IL-10, are part of a negative feedback circuit that contro
ls acute inflammatory response.