The JAK-STAT signaling pathway is fundamental for immune system regulation. It involves phosphorylation of several types of STAT proteins in response to binding of cytokines to immune cell receptors. Traditionally, the immune signaling studies focus on measuring the levels of phosphorylated STATs (pSTATs) following individual cytokine application. We developed an experimental approach, based on multiparametric flow cytometry, to simultaneously measure the levels of five pSTATs after 15 minutes of cell treatment with high doses of individual cytokines and their paired combinations.
Analysis of our experimental data involving peripheral blood mononuclear cells from healthy donors reveals systematic suppression of IL-10R, IL-6R, and IL-2Rβγ signaling in T cells, B cells, NK cells, and monocytes. This suppression is mediated by at least all tested cytokines that do not induce relevant pSTATs by themselves. Remarkably, the cytokines with negligible own signaling do act as prominent selective signaling suppressors. In contrast, the signaling of IFNAR, IFNGR, IL-4R, and IL-2Rαβγ remains largely unaffected by co-application of other cytokines.
We propose that this pattern of signaling suppression represents an evolutionary developed mechanism enhancing the promptness, specialization, and efficiency of the immune response, while increased concentration of cytokines serves as a danger signal of inefficient response. We hypothesize that selective signaling suppression arises from the differential sensitivity of conformations of cytokine-receptor complexes to the increase of cell surface tension and stiffness, which is caused by effects following the binding of cytokines to membrane-associated molecules, including glycocalyx elements. While the rewiring of immune cell signaling should represent a powerful evolutionary tool for augmentation of adaptive response, it should also lead to the prolonged suppression of counteracting signaling pathways, culminating in cytokine release syndrome and contributing to autoimmune diseases.