Fever-range temperature alters continual efferocytosis mediated by mouse proinflammatory macrophages

Fever, a cardinal sign of inflammation, has been shown to modulate macrophage functions. Here, we investigate whether fever affects macrophage efferocytosis. This process is essential for the resolution of inflammation and the return to homeostasis with the reprogramming of macrophages toward a proresolving phenotype. Using primary mouse bone marrow-derived macrophages stimulated with lipopolysaccharide and interferon-γ (ie proinflammatory macrophages), we first validated that exposure to febrile temperature (39.5 °C) induced a heat shock protein response. Then, we observed that febrile temperature decreased the capacity of proinflammatory macrophages to uptake apoptotic cells. This reduced efferocytic capacity of macrophages exposed to febrile temperature resulted from a decreased capacity to interact with apoptotic cells and to internalize these dying cells. Exposure to febrile temperature reduced the cell motility of macrophages in response to apoptotic cells, as assessed by IncuCyte live-cell imaging. RNA sequencing analysis of proinflammatory macrophages exposed to febrile temperature identified an upregulation of the Adam17 gene. As this gene encodes a protease that sheds the efferocytic receptor Mer, we determined cell surface expression of Mer and quantified soluble Mer in the culture supernatants of proinflammatory macrophages exposed to febrile temperature. While febrile hyperthermia induced the Mer cleavage from the cell surface of proinflammatory macrophages, ADAM17 inhibition during exposure to febrile temperature did not restore the efferocytic capacity of proinflammatory macrophages. Thus, reduction of Mer expression induced by hyperthermia did not represent the main mechanism explaining reduced efferocytosis. Nevertheless, our work suggests that fever, by decreasing the efferocytic capacity of macrophages, maintains their proinflammatory state.