Macrophage phenotypes and Gas6/Axl signaling in apical lesions

Macrophages participate in the periapical inflammation with pro-inflammatory M1 cells and anti-inflammatory M2 cells. Gas6/Axl signal is the responsible pathway for the activation of M1 and polarization of M2. The aim of this study was to compare the number of CD16⁺ M1 cells, CD206⁺ M2 cells, and Gas6/Axl expression between apical granulomas and radicular cysts.

Twenty-four cases of granuloma and twenty of cysts were submitted to immunohistochemistry using anti-CD16 and anti-CD206 antibodies for determining M1 and M2 macrophages and investigating the cells with positive Gas6 and Axl expression.

There were more numerous of M1 macrophages in radicular cysts (175.9 ± 87.7) compared to apical granuloma (116.6 ± 55.8), and M2 macrophages was higher in cysts (204.0 ± 97.6) than granuloma (152.9 ± 64.6). The level of Gas6/Axl expression were similar. There was a significant different in M1 macrophage (P = 0.014) between two diagnosis. In patients with or without root resorption, the number of M1 were 194.6 ± 57.2 compared with 139.1 ± 79.6. The number of M2 were 241.7 ± 81.4 and 164.6 ± 77.1. The expression of Axl was stronger in root resorption patients (191.1 ± 43.6), but the tendency in Gas6 expression was similar. Significant differences were noted in high M2 infiltration and Axl positive lesions.

It appears that macrophages associated with significantly higher numbers in radicular cysts than apical granuloma. Meanwhile, macrophages and Axl receptor was intensively expressed in patients with root resorption, related to severe inflammation.