IFNγ Causes Keratinocyte Necroptosis in Acute Graft-Versus-Host Disease.

Epidermal keratinocytes form the first-line cellular barrier of the skin for protection against external injuries and maintenance of local tissue homeostasis. Expression of ZBP1 was shown to cause necroptotic keratinocyte cell death and skin inflammation in mice. We sought to characterize the relevance of ZBP1 and necroptosis in human keratinocytes and type 1-driven cutaneous acute graft-versus-host disease. in this study, we identify ZBP1 expression, necroptosis, and interface dermatitis as being the hallmarks of acute graft-versus-host disease. ZBP1 expression was dependent on leukocyte-derived IFNγ, and interference with IFNγ signaling by Jak inhibition prevented cell death. In predominantly IL-17-driven psoriasis, both ZBP1 expression and necroptosis could not be detected. Of note, in contrast to the signaling in mice, ZBP1 signaling in human keratinocytes was not affected by RIPK1's presence. These findings show that ZBP1 drives inflammation in IFNγ-dominant type 1 immune responses in human skin and may further point to a general role of ZBP1-mediated necroptosis.

Detection of In Vivo Inflammasome Activation for Predicting Sepsis Mortality.

Sepsis is a severe life-threatening syndrome caused by dysregulated host responses to infection. Biomarkers that allow for monitoring the patient's immune status are needed. Recently, a flow cytometry-based detection of in vivo inflammasome activation by formation of cytoplasmic aggregates of ASC (apoptosis-associated speck-like protein containing a caspase recruitment domain) has been proposed. Here we report on the frequency of ASC-speck+ leukocytes correlating with the survival of sepsis. 25 patients with sepsis were sampled consecutively for 7 days. Blood, serum samples and patient data were collected according to the guidelines of the PredARRT-Sep-Trial. Flow cytometric analysis was performed on fresh whole blood samples to investigate the formation of ASC-specks in leukocyte subsets. Serum samples were analyzed for production of IL-1ß, IL-18 and additional inflammatory markers. ASC-speck formation was found to be increased in leukocytes from sepsis patients compared to healthy donor controls. The absolute number of ASC-speck+ neutrophils peaked on day 1. For monocytes, the highest percentage and maximum absolute number of ASC-speck+ cells were detected on day 6 and day 7. Inflammatory cytokines were elevated on day 1 and declined thereafter, with exception of IL-18. Survival analysis showed that patients with lower absolute numbers of ASC-speck+ monocytes (<1,650 cells/ml) on day 6 had a lower probability to survive, with a hazard ratio (HR) of 10.178. Thus, the frequency of ASC-speck+ monocytes on day 6 after onset of sepsis may serve to identify patients at risk of death from sepsis.

ERK/p38 MAP-kinases and PI3K are involved in the differential regulation of B7-H1 expression in DC subsets.

Regulatory molecules of the B7-H-family expressed by DC are important for immune homeostasis, but their regulation is largely unknown. When investigating the pathways regulating B7-H1 expression in monocyte-derived DC (MoDC), freshly isolated myeloid DC (mDC) and plasmacytoid DC, respectively, we showed that in MoDC and mDC B7-H1 expression was upregulated by a standard cytokine cocktail, poly I:C or LPS. MoDC utilize ERK and PI3K pathways to upregulate B7-H1 in response to cytokines, whereas p38 kinase was predominantly utilized in response to poly I:C. In mDC, ERK and p38 pathways are involved in B7-H1 regulation, and similar to MoDC, mainly p38 signaling was required for poly I:C-induced expression of B7-H1. Plasmacytoid DC responded only to CpG with upregulation of B7-H1 and in addition to p38 also utilized the PI3K and ERK pathways to regulate B7-H1 expression. As a functional consequence of B7-H1 expression on DC, we demonstrate downmodulation of IFN-gamma production in T cells. Thus, the differential regulation of B7-H1 on DC subsets may suppress immune responses variably, depending on the target DC population. Further analysis of the regulatory mechanisms may facilitate the development of new immunosuppressive therapies, utilizing the regulation of B7-H1 expression on DC.