Macrophages differentiation in the C3a presence: influence on efferocytosis

Background. Macrophages are unique cells as professional phagocytes that take part in the innate and adaptive immune response. This is possible due to the functional plasticity of macrophages: ability to acquire different phenotypes. Switching between subtypes when macrophages interact with other elements of the immune system is called polarization. Anaphylotoxin C3a has been shown to influence macrophage polarization. At the same time, depending on polarization, macrophages exhibit different phagocytic activity. Since C3a effect on macrophages is controversial, resolving the issue of C3a influence on phagocytosis in general and efferocytosis of macrophages in particular is interest.

Aim – to investigate the effect of anaphylotoxin C3a on efferocytosis by M0 and M2 macrophages.

Materials and methods. Experiments were performed applying peripheral blood mononuclear cells. Macrophages were differentiated in the presence of C3a, and polarization to the M2 phenotype was executed using interleukin-4. Efferocytosis was estimated by confocal microscopy, and phagocytosis was assessed by flow cytofluorometry. Real-time PCR was applied to set up the expression of the efferocytosis receptor genes mertk, axl, and tyro3.

Results. M2 macrophages have a high potential for efferocytosis compared to M0 macrophages. Anaphylatoxin C3a doesn`t impact on E.coli-FITC phagocytosis, but inhibits apoptotic cells phagocytosis in both non-polarized macrophages and alternatively activated M2 macrophages. Moreover, it has been shown that C3a reduces receptor gene Tyro 3 expression in both M0 and M2 macrophages.

Conclusions. Anaphylatoxin C3a has an inhibitory effect on efferocytosis, which is probably realized through the regulation of apoptotic cells recognition processes.