Quantification of indoleamine 2,3-dioxygenase gene induction in atopic and non-atopic monocytes after ligation of the high-affinity receptor for IgE, FcεRI and interferon-γ stimulation

Antigen-presenting cells (APCs) are crucial in regulating the outcome of T cell responses. Certain APCs are able to down-regulate T cell proliferation in vitro by inducing the enzyme indoleamine 2,3-dioxygenase (IDO) upon interferon-γ(IFN-γ) stimulation. IDO is the rate-limiting enzyme in the catabolism of the essential amino acid tryptophan. A lack of extracellular tryptophan creates environments in which cells become starved for this amino acid. The high-affinity receptor for IgE, FcεRI, is the principal receptor for the binding of specific IgE in type I-mediated allergies. We demonstrated recently that IDa is overexpressed in FcεRI-stimulated monocytes. In the present study, we performed quantification of IDO gene induction after treatment of atopic (FcεRI^high) and non-atopic (FcεRI^low/-) monocytes with IgE/anti-IgE and IFN-γ. By quantitative PCR ELISA, we found IDO molecule induction in atopic monocytes was enhanced about 50-fold over non-atopic monocytes after ligation of FcεRI. Stimulation with IFN-γ at a concentration of 100 U/ml in culture medium caused an increase in IDO gene copy numbers in atopics of about fourfold over that of non-atopics. This comparative quantification study demonstrates clearly the regulation of IDO gene expression by FcεRI and discloses differences thereof in atopic and non-atopic cells upon inflammatory stimuli.