Abstract
Pyroptosis is a programmed and inflammation-inducing cell death that occurs predominantly in macrophages. It is characterized by the inflammasome-mediated activation of caspase-1, leading to cell lysis. During pyroptosis, pro-inflammatory mediators such as IL-1β are released extracellularly to further recruit and activate other immune cells. Thus, pyroptosis plays a crucial role in the prevention of the spread of pathogens. The clinically applied synthetic glucocorticoid, hydrocortisone (HC), has strong immunoregulatory properties. It may act as an immunosuppressive agent by negatively regulating pro-inflammatory gene transcription but has also shown immune-sensitizing properties. The conditions that determine the immunosuppressive or immune-sensitizing actions of HC during an infection are not fully clear. We hypothesized that the outcome may differ depending on the onset and duration of its administration. Therefore, we investigated the impact of acute (treatment upon infection) and chronic (24 h pre-treatment before infection) HC treatment on pyroptosis induction and execution in THP-1 macrophage-like cells. The focus was on pyroptosis-associated signaling pathways, inflammasome assembly and activation, IL-1β, and cell death. Physiological HC concentration and HC deprivation were used as controls. Compared to the physiological concentration, cells displayed augmented inflammasome activation and IL-1β release following acute HC treatment. Conversely, the whole pyroptosis machinery was suppressed by chronic HC administration. These in vitro investigations demonstrate pro-inflammatory actions of acute HC exposure and the immunosuppressive effects of chronic treatment. These differential effects on pyroptosis emphasize the importance of individualized HC medication in patients upon infection, and suggest the inclusion of IL-1β as a marker for current immune capacities.