The effect of enhancing antibodies on TNF interactions with its specific receptor: Consequences for in vitro TNF antiviral activity

This study examines the interaction of TNF with its receptor(s) in the presence of antibodies which have been previously found to enhance the in vivo antiviral and antitumor activities of this cytokine. The presence of Mab 32 has been previously shown to enhance the binding of ¹²⁵I-TNF to the surface L929 cells (13), and this property was also found in the present study for HeLa cells. In addition to this, Mab 32 was found to enhance the internalization of the TNF ligand into both L929 and HeLa cells compared to control treated cultures. The consequences of such enhanced TNF-binding on TNF antiviral activity were examined in both L929 cells and HeLa cells. It was discovered that the similarities in antibody-enhanced TNF binding and internalization contrasted dramatically with the sensitivities of these two cell lines to the antiviral actions of TNF, both with and without Mab 32 (viz., L929 cells were sensitive; HeLa cells were resistant). It has been proposed that the modulation of TNF-R expression, particularly by IFNs, is an important factor in TNF's biological effects. It has been shown that the presence of IFN-γ, with TNF plus specific enhancing antibodies, further augmented antiviral activity in vivo (13). This finding stimulated interest in examining IFN-γ modulation of TNF-R as a factor in the antiviral activity of TNF. The expression of TNF receptor(s) in TNF- and/or IFN-γ-exposed cells, both with and without HSV-1 infection, was therefore examined. TNF alone could induce a dose-dependent increase in receptor expression which was not significantly increased by Mab 32. Exposure of L929 cells to TFN-γ alone also induced TNF receptor expression in mock-infected cells. HSV-1 infection of L929 cells resulted in a significant upregulation of TNF-R expression which was reversed if the cells had been preexposed to IFN-γ. The inclusion of TNF with IFN-γ before infection restored TNF-R expression but did not show any further synergistic or additive effects on TNF-R expression Some minor increases in TNF-R expression were seen if Mab 32 was included with these two cytokines.