Three cell deaths and a funeral: macrophage clearance of cells undergoing distinct modes of cell death.

Macrophage clearance of apoptotic cells has been extensively investigated, but less is known regarding the clearance of cells dying by other forms of programmed cell death, e.g., necroptosis or ferroptosis. Here, we established a model of three different cell deaths using the same cell line and the occurrence of distinct cell death modalities was verified by using the specific inhibitors, zVAD-fmk, necrostatin-1, and ferrostatin-1, respectively. Cell death was characterized by using transmission electron microscopy (TEM), the gold standard for the demarcation of different cell death modalities. Moreover, using annexin V as a probe, we could detect surface exposure of phosphatidylserine (PS) in all three types of cell death, and this was confirmed by using specific anti-PS antibodies. We then co-cultured the cells with human monocyte-derived macrophages and found that cells dying by all three death modalities were engulfed by macrophages. Macrophage clearance of apoptotic cells was more efficient when compared to necroptotic and ferroptotic cells with multiple internalized target cells per macrophage, as shown by TEM. We propose that clearance of dying cells also should be taken into account in the classification of different cell death modalities.