Effect of methotrexate-induced neutropenia on rat periapical lesion.

We investigated the effect of methotrexate-induced neutropenia on periapical lesions in rats. Periapical lesions were prepared in all animals by pulpal exposure. The animals were injected with methotrexate three times a week 4 weeks before or after the pulpal exposure. The periapical lesion of each animal was examined histologically, histometrically, and immunohistochemically. The total leukocyte count and neutrophil count in the peripheral blood decreased after the injection. The methotrexate-induced neutropenia elicited after pulpal exposure did not change the status of the periapical lesion, whereas the neutropenia before the exposure inhibited the development of the lesion. Moreover, the neutropenia before pulpal exposure resulted in an inhibition of infiltration of neutrophils into the lesion.