Advanced glycation endproducts induce self- and cross-tolerance in monocytes

Advanced glycation endproducts (AGEs) are well-known inflammatory mediators, which are recognized by immune cells through their corresponding receptor RAGE and have been shown to participate in the pathophysiology of a variety of acute as well as chronic inflammatory diseases. Nevertheless, no data are available on the aftermath of AGE recognition on immune cells. We used the monocytic cell line MonoMac6 as well as primary human monocytes for double stimulation experiments. We measured secreted as well as intracellular levels of TNF-α using ELISA and flow cytometry. In addition, gene expression of surface receptors (RAGE and TLR4) and TNF were measured by qPCR. Stimulation with AGE leads to a dose-dependent induction of self- and cross-tolerance in both primary monocytes as well as the MonoMac6 cell line. The AGE tolerance depended neither on a decreased expression of RAGE or TLR4, nor on a decrease of TNF-α expression. Nevertheless, intracellular TNF-α was decreased, hinting towards a posttranscriptional regulation. High levels of AGEs are capable to activate immune cells at first, but induce a secondary state of hypo-responsiveness in these cells. Based on the origin of its causal agent, we propose this phenomenon to be “metabolic tolerance”.