Effects of methotrexate on trophoblast proliferation and local immune responses.

Methotrexate is a folic acid analogue that has been used successfully for the treatment of ectopic pregnancy and, in conjunction with misoprostol, for medical abortions of early intrauterine pregnancies. To administer the most efficacious treatment requires knowledge of the mechanism underlying the induction of methotrexate-induced abortion. This study was designed to ascertain trophoblast integrity, proliferation and differentiation following administration of methotrexate. In addition, to determine if methotrexate affects the local uterine immune response, we ascertained the numbers and identities of decidual leukocytes following treatment. Ten women with undesired intrauterine pregnancies of 42-49 days gestation were recruited to receive methotrexte 50 mg/m2 i.m. A suction aspiration was performed 7 days later. Tissues from gestational age-matched elective surgical abortions were used as controls. Additionally, specimens from women who received methotrexate and misoprostol for abortion in a clinical trial of oral methotrexate in combination with misoprostol, who had a suction abortion because of continued embryonic cardiac activity 14 days after the methotrexate, were evaluated. Immunoreactivity to proliferating cell nuclear antigen and cyclin D3 antibodies was used to demonstrate a marked reduction in the proliferation index of cytotrophoblasts from methotrexate-treated abortions. Methotrexate treatment failures and non-treated pregnancies had a much higher proliferation index. There was no direct destruction of the syncytiotrophoblast, as indicated by the continued presence of human placental lactogen and beta-human chorionic gonadotrophin proteins. A decrease in the total number of leukocyte cells was observed in the decidua of methotrexate-treated samples, with the large granular lymphocyte (LGL) cells showing the greatest decline in numbers. Our conclusions from this study are that methotrexate acts primarily to derail the normal developmental programme of the trophoblast stem cell population, as well as to decrease LGL cell numbers in the decidua.