Innate Immune Activation

Moritz M. Gaidt, Francesca Rapino, Thomas Graf, Veit Hornung

Monocytes and macrophages play a pivotal role in the induction and shaping of immune responses. Expressing a broad array of pattern recognition receptors (PRRs), monocytes and macrophages constitute an integral component of the innate branch of the immune system. Traditionally, the majority of innate immune sensing and signaling pathways have been studied in macrophages of the murine system. This is largely due to the fact that genetic loss-of-function studies are amenable in this species. On the other hand, human cell lines of the monocyte-macrophage cell lineage have been widely used to study myeloid cells in vitro. However, commonly utilized models (e.g., THP-1 cells) only mimic a limited spectrum of the immunobiology of primary human myeloid cells. Recently, we have explored the possibility to fill this gap with a human trans-differentiation cell culture system, in which lineage conversion from malignant B-lineage cells to monocytes/macrophages is caused by the inducible nuclear translocation of a C/EBPα transgene, BLaER1 cells. Using this model, we were able to characterize a novel inflammasome signaling entity that could not have been uncovered in the murine system or THP-1 cells. Here, we describe the handling of BLaER1 cells, providing a detailed protocol for their induced trans-differentiation. We also provide data to demonstrate the applicability of the BLaER1 monocyte/macrophage system to study phagocytosis and various PRR cascades in human cells.