The expression of I‐A correlates with the uptake of interferon‐γ by macrophages

Abstract

The current studies were designed to examine some of the requirements for I-A expression when macrophages (MΨ) were treated with interferon-gamma (IFN-γ). In order to define the minimum time required for IFN-γ to induce surface expression of I-A antigen on bone marrow-derived MΨ, cells were incubated with IFN-γ for varying lengths of time, washed and thereafter incubated for 72 h before assaying I-A surface expression. Using saturating amounts of IFN-γ (300 IRU/ml), we found that between 0 and 30 min of IFN-γ treatment there is a direct correlation between the length of treatment and the level of I-A surface expression. When the steady state level of RNA for the I-A_β gene was assayed, a low level of I-A_β RNA was seen in cells treated for 10 min with saturting amounts of IFN-γ (300 IRU/ml) while a 30-min or 60-min exposure of cells to the same concentration of IFN-γ resulted in a steady increase in the level of I-A_β RNA. Similar results were found when we measured the levels of RNA for the tumor necrosis factor and C3 complement genes, both of which are induced by IFN-γ in MΨ. MΨ treated with low amounts of IFN-γ (3 IRU/ml) for 30 min do not express cell surface I-A. Cells incubated continuously for 72 h with 3 IRU/ml of IFN-γ expressed a level of I-A on the surface equivalent to the level of I-A expressed on cells treated for only 30 min with 300 IRU/ml of IFN-γ. Based on the observed correlation between either the IFN-γ concentration or the length of time the cells were exposed to IFN-γ, or the level of I-A expression on MΨ, we conclude that the expression of I-A correlates with the uptake of IFN-γ.