Monocyte Derived Macrophage (MDM) responses to heme stimulation

Abstract

In hemolytic conditions such as sepsis and sepsis-induced Acute Respiratory Distress Syndrome (ARDS), elevated concentrations of red blood cell degradation products like cell free heme are present in patients and have been associated with poor clinical outcomes. Previously, we and others have reported that cell free heme is cytotoxic, pro-inflammatory and induces alveolar epithelial barrier disruption <i>in vitro</i>. To better understand underlying mechanisms of heme-induced injury, apart from alveolar barrier integrity, characterization of immune cell responses to heme stimulation are required. For this purpose, monocyte derived macrophages (MDMs) from three healthy volunteers were generated and stimulated with 100µM heme for 24h. Apoptosis induction and surface marker expression (CD14, CD86, CD91, CD163, CD206 and MHC-II) were measured <i>via</i> flow cytometry. Additionally, supernatants were collected, and multiplex analysis was performed. In this study we show that heme does not have any effect on MDM apoptosis and surface marker expression. However, the levels of several pro-inflammatory cytokines are increased in response to heme stimulation <i>in vitro</i> compared to untreated controls. Overall, our results indicate that the role of heme in macrophages is associated with pro-inflammatory cytokine secretion, while surface marker expression and apoptosis remained unaltered. Further studies are ongoing to investigate the role of heme stimulation at the gene and protein levels.