Transforming Growth Factor-μ Inhibits the Antiviral Action of Interferons in Human Embryonic Fibroblasts

Transforming growth factor-beta inhibits interferon-gamma-induced HLA-DR expression by cultured human fibroblasts

This study shows the induction of HLA-DR (DR) in fibroblasts by IFN-gamma and investigates the molecular mechanisms involved in the further DR down-regulation by TGF-beta 1. Kinetics of DR induction on human dermal fibroblasts by IFN-gamma showed that 1 hr of exposure was required to induce detectable levels of DR, and maximal DR expression was achieved only after 2 days of exposure to IFN-gamma. TGF-beta 1 inhibited DR induction by IFN-gamma, although complete inhibition never could be achieved, even with high concentrations of TGF-beta 1 and low concentrations of IFN-gamma. Inhibition was not accounted for by reduction in cell numbers, as TGF-beta 1 stimulated growth of the fibroblasts. Inhibition of DR induction was seen only if TGF-beta 1 was added during the first 24 hr of IFN-gamma treatment. TGF-beta 1 inhibited equally well if the cells were pretreated for as little as 1 hr and then washed before addition of IFN-gamma. TGF-beta 1 did not cause an overall suppression of protein synthesis. Northern blot analysis revealed that TGF-beta 1 greatly reduced the steady-state level of DR beta mRNA induced by IFN-gamma at 24 hr, and then DRP transcripts became undetectable at later stages. It is concluded that early intracellular signals must build up to stimulate maximum DR synthesis, which, later on, are inactivated or degraded by the action of TGF-beta 1. We suggest that these mechanisms regulating DR gene transcription involve the action of genes coding for specific IFN-gamma-inducible transcriptional factors that are turned on and off in an expeditious manner.

Sensitive antiproliferative neutralization assay for the detection of neutralizing IFN-alpha and IFN-beta antibodies

Antibodies to interferon (IFN) may compromise IFN treatment in some patients. In tumor therapy, a critical function of type I IFNs is their antiproliferative effect. For the quantification of neutralizing IFN antibodies we have developed an antiproliferative neutralization assay (APA) based on the reduction of IFN-mediated growth inhibition of Daudi cells by IFN-alpha and IFN-beta antibodies. Proliferation was quantified by [3H]thymidine incorporation, and the neutralizing potency of IFN antibody-positive sera was expressed as the neutralizing titer inhibiting 50% of the antiproliferative activity of 10 IU/ml of IFN (NT50). The APA is easy to perform, reproducible, and more sensitive than a well-established antiviral neutralization assay (AVA). All 30 sera with recombinant IFN-alpha 2a-binding antibodies proved to be neutralizing antibody-positive in the APA whereas seven were scored antibody-negative or uninterpretable in the AVA. The APA is recommended as a second or third line assay for the estimation of the neutralizing potency of spontaneous or treatment-induced IFN-alpha and IFN-beta-specific antibodies.

Effects of transforming growth factor-beta 1 against the inhibitory action of interferon on DNA synthesis and viral replication in hepatitis B virus DNA-transfected cell

Studies were undertaken to examine the effects of recombinant human transforming growth factor beta 1 (TGF-beta 1) on DNA synthesis and antiviral actions of interferons (IFNs) in HepG2 cell, a hepatoma cell line, transfected with hepatitis B virus (HBV) DNA. The inhibitory effects of IFN-alpha and -gamma on DNA synthesis of HepG2 cells were enhanced in a dose-dependent manner by a simultaneous addition of TGF-beta. The degree of suppression by the reagents was greater in HBV-nontransfected cells than in transfected cells. Inhibition of DNA synthesis was not due to direct cytotoxic effects of the additives, since the viability of HepG2 cells was comparable in the control and treated cultures as determined by trypan blue exclusion. Treatment of HBV DNA-transfected HepG2 cells with IFNs resulted in decrease in production of HB surface and e antigens, and in the level of HBV DNA, but TGF-beta reversed the IFN-induced antiviral state in HBV DNA-transfected HepG2 cells. TGF-beta had no direct effect on HBV replication. These results indicate that rTGF-beta 1 exerts a differential effect against the inhibitory actions of IFN on DNA synthesis and viral replication in HepG2 cells.