TNF-ALPHA REGULATES IL-4-INDUCED FC-EPSILON-RII/CD23 GENE-EXPRESSION AND SOLUBLE FC-EPSILON-RII RELEASE BY HUMAN MONOCYTES

We examined the regulatory effects of TNF-alpha on IL-4-induced gene expression of the low-affinity receptor for IgE (Fc epsilon RII/CD23) in human monocytes and IL-4-induced soluble Fc epsilon RII (sFc epsilon RII) release from monocytes. IL-4-induced Fc epsilon RII expression on the surface of monocytes was reduced by TNF-alpha as early as 1 day after culture and the effect of TNF-alpha increased with prolonged culture. The present analysis was designed to examine whether or not TNF-alpha could suppress IL-4-induced Fc epsilon RII mRNA expression and enhanced IL-4-induced sFc epsilon RII release, The addition of TNF-alpha to monocyte cultures with IL-4 significantly reduced Fc epsilon RII expression on the surface of monocytes and significantly increased sFc epsilon RII release from monocytes. Over time, there was an inverse relationship between the disappearance of cell surface Fc epsilon RII and the appearance of sFc epsilon RII in culture supernatants. Fc epsilon RII mRNA expression in monocytes cultured with IL-4 was not affected by TNF-alpha when examined at 6 h after cultivation. When the cells were cultured with TNF-alpha for more than 24 h, however, TNF-alpha down-regulated IL-4-induced Fc epsilon RII mRNA levels, This correlated with the kinetics of down-regulation of IL-4-induced Fc epsilon RII expression on the surface of monocytes by TNF-alpha, These results suggest that TNF-alpha-dependent reduction of IL-4-induced Fc epsilon RII expression on the surface of monocytes resulted, at least in part, from the suppression of Fc epsilon RII mRNA expression and the enhancement of sFc epsilon RII release.