A histochemical study of the behavior of macrophages during experimental apical periodontitis in rats

The behavior of macrophages from experimentally induced periapical lesions of rats was studied in paraffin sections using nonspecific esterase and a monoclonal antibody, ED1. Macrophages were seen near the regularly arranged osteoblasts in controls and the detached osteoblasts at the initiation phase of bone resorption. In addition, numerous macrophages were widely distributed throughout the periodontium at the activation phase of bone resorption. On the other hand, macrophages were rarely seen near the bone formation surfaces, but large numbers of macrophages were localized in microabscess at the activation phase of bone formation. It is suggested that macrophages may play an important role in activation of osteoclastic bone resorption and inhibition of complete bone repair in bone remodeling during experimental apical periodontitis.