Key Points Novel GM-CSF signaling pathways through IFN-γR/IRF-1 and AKT/mTOR provide monocyte licensing for suppressor function. Only licensed but not fresh Ly-6Chigh murine or human CD14+ monocytes secrete nitric oxide or IDO for T-cell suppression.

Budde K (2022) The natural history of de novo donor-specific HLA antibodies after kidney transplantation.

Interleukin (IL)‐6‐type cytokines have no direct antiviral activity; nevertheless, they display immune‐modulatory functions. Oncostatin M (OSM), a member of the IL‐6 family, has recently been shown to induce a distinct number of classical interferon stimulated genes (ISG). Most of them are involved in antigen processing and presentation. However, induction of retinoic acid‐inducible gene (RIG)‐I‐like receptors (RLR) has not been investigated. Here we report that OSM has the capability to induce the expression of the DExD/H‐Box RNA helicases RIG‐I and melanoma differentiation antigen 5 (MDA5) as well as of the transcription factors interferon regulatory factor (IRF)1, IRF7 and IRF9 in primary fibroblasts. Induction of the helicases depends on tyrosine as well as serine phosphorylation of STAT1. Moreover, we could show that the OSM‐induced STAT1 phosphorylation is predominantly counter‐regulated by a strong STAT3‐dependent SOCS3 induction, as Stat3 as well as Socs3 knock‐down results in an enhanced and prolonged helicase and IRF expression. Other factors involved in regulation of STAT1 or IRF1 activity, like protein tyrosine phosphatase, non‐receptor type 2 (PTPN2), promyelocytic leukaemia protein (PML) or small ubiquitin‐related modifier 1 (SUMO1), play a minor role in OSM‐mediated induction of RLR. Remarkably, OSM and interferon‐γ (IFN‐γ) synergize to mediate transcription of RLR and pre‐treatment of fibroblasts with OSM fosters the type I interferon production in response to a subsequent encounter with double‐stranded RNA. Together, these findings suggest that the OSM‐induced JAK/STAT1 signalling is implicated in virus protection of non‐professional immune cells and may cooperate with interferons to enhance RLR expression in these cells.

Interleukin-27 (IL27) is a type-I cytokine of the IL6/IL12 family and is predominantly secreted by activated macrophages and dendritic cells. We show that IL27 induces STAT factor phosphorylation in cancerous cell lines of different tissue origin. IL27 leads to STAT1 phosphorylation and recapitulates an IFN-γ-like response in the microarray analyses, with up-regulation of genes involved in antiviral defense, antigen presentation, and immune suppression. Like IFN-γ, IL27 leads to an up-regulation of TAP2 and MHC-I proteins, which mediate increased tumor immune clearance. However, both cytokines also upregulate proteins such as PD-L1 (CD274) and IDO-1, which are associated with immune escape of cancer. Interestingly, differential expression of these genes was observed within the different cell lines and when comparing IL27 to IFN-γ. In coculture experiments of hepatocellular carcinoma (HCC) cells with peripheral blood mononuclear cells, pre-treatment of the HCC cells with IL27 resulted in lowered IL2 production by anti-CD3/-CD28 activated T-lymphocytes. Addition of anti-PD-L1 antibody, however, restored IL2 secretion. The levels of other T 1 cytokines were also enhanced or restored upon administration of anti-PD-L1. In addition, we show that the suppression of IL27 signaling by IL6-type cytokine pre-stimulation-mimicking a situation occurring, for example, in IL6-secreting tumors or in tumor inflammation-induced cachexia-can be antagonized by antibodies against IL6-type cytokines or their receptors. Therapeutically, the antitumor effects of IL27 (mediated, e.g., by increased antigen presentation) might thus be increased by combining IL27 with blocking antibodies against PD-L1 or/and IL6-type cytokines.

The pro-inflammatory cytokines tumor necrosis factor (TNF), interleukin-1 (IL-1) and interleukin-6 (IL-6) are key players of the innate and adaptive immunity. Their activity needs to be tightly controlled to allow the initiation of an appropriate immune response as defense mechanism against pathogens or tissue injury. Excessive or sustained signaling of either of these cytokines leads to severe diseases, including rheumatoid arthritis, inflammatory bowel diseases (Crohn's disease, ulcerative colitis), steatohepatitis, periodic fevers and even cancer. Studies carried out in the last 30 years have emphasized that an elaborate control system for each of these cytokines exists. Here, we summarize what is currently known about the involvement of receptor endocytosis in the regulation of these pro-inflammatory cytokines' signaling cascades. Particularly in the last few years it was shown that this cellular process is far more than a mere feedback mechanism to clear cytokines from the circulation and to shut off their signal transduction.