The expression of PD-1 and LAG-3 in periapical lesions.

Periapical lesions are the distinct result of chronic root canal infection and could generate severe bone resorption surrounding apical regions. Despite the local cytokine and cell-mediated immune responses, periapical lesions are also characterized by its auto-restrict inflammation. However, the detailed mechanism related to its auto-restriction of immune response is still unclear. Co-inhibitory immune checkpoints are important molecules which could negatively modulate immune response especially in T cell function. In this study we detected the expressional pattern of PD-1/LAG-3 in periapical lesions. Immunohistochemical staining showed that the inflammatory response including up-regulation of TNF-α and the infiltration of T cells, was severe in granuloma and restricted in periapical cyst. PD-1 and LAG-3 both could be detected in granuloma and cyst, while scarcely observed in control group. Exhausted T cells, characterized by PD-1 or LAG-3 positive, accumulated within granuloma and reduced in cyst. Our study revealed that in periapical lesions, T cell exhaustion characterized by PD-1 or LAG-3 positive, might contribute to the auto-restriction of inflammatory response in periapical lesions.