Differentiation of macrophages in the presence of anaphylatoxin C3a: effect on efferocytosis

BACKGROUND: Macrophages are unique professional phagocytes involved in both innate and adaptive immune responses. This is made possible by their functional plasticity—the ability to acquire different phenotypes. Switching between subtypes during interactions with other immune system components is referred to as polarization. Anaphylatoxin C3a has been shown to influence macrophage polarization. Depending on the polarization state, macrophages exhibit different phagocytic activities. Given the contradictory evidence regarding C3a’s effects on macrophages, determining its impact on phagocytosis in general and on efferocytosis in particular is of special interest. AIM: The work aimed to investigate the effect of anaphylatoxin C3a on efferocytosis by M0 and M2 macrophages. METHODS: The experiments were conducted using human peripheral blood mononuclear cells. Macrophages were differentiated in the presence of C3a, and M2 polarization was induced with interleukin-4. Efferocytosis was assessed using confocal microscopy, whereas phagocytosis was evaluated via flow cytometry. Real-time reverse transcription polymerase chain reaction was used to measure expression of the efferocytosis receptor genes mertk, axl, and tyro3. RESULTS: M2 macrophages demonstrated greater efferocytic capacity compared to M0 macrophages. Anaphylatoxin C3a did not affect the phagocytosis of dead Escherichia coli bacteria but inhibited the phagocytosis of apoptotic cells in both unpolarized M0 and alternatively activated M2 macrophages. It was also shown that C3a reduces the expression of the Tyro3 receptor gene in both M0 and M2 macrophages. CONCLUSION: Anaphylatoxin C3a exerts a suppressive effect on efferocytosis, likely through modulation of apoptotic cell recognition processes.