Augmentation of immune responses after methotrexate administration.

A single intraperitoneal injection of 0.5 mg methotrexate (MTX) has been found to increase the immune reactivity of spleen cells from (C57B1/6 X DBA/2)F1 mice. Five days after injection, spleen cells from MTX-treated mice exhibited greater PHA responsiveness and GvH reactivity, and mice given SRBC at this time developed greater than normal direct PFC responses. This pattern of effects of MTX was particularly evident in mice that had been given high doses of BCG intravenously 14 days before testing, a treatment that generally depressed the measured activities. MTX enhancement of GvH was also observed in mice that had been depleted of short-lived T lymphocytes by adult thymectomy. We suggest that MTX-sensitive cells possible exert, particularly in BCG-treated mice, a suppressive action on the responding cells.