In our study, both CD68+iNOS+ M1 and CD68+CD206+ M2 subtypes of macrophages were quantified in periapical lesion tissues collected from patients with pre-treated AP plus intact coronal restoration and no signs of root fracture, which suggested persistent and uncontrolled infection.46,47 Infiltrated M1 macrophages in these apical lesion tissues were significantly more abundant compared with M2 macrophages. Here, MRC1 is linked to alkaline phosphatase measurement.