The kinetics of inhibition with methotrexate and vinblastine of the primary immune response to sheep red blood cells in mice.

Forty-eight or 72 h after immunization with sheep red blood cells, CBA mice were injected intraperitoneally with a single dose of methotrexate or vinblastine, 2.5 mg/kg and 1.5 mg/kg respectively, and then the number of direct plaque-forming cells in their spleen was estimated at 4-h intervals. The PFC growth curve showed an exponential and staircase pattern. After administration of both cytostatics, the PFC numbers in the spleen of mice changed in a wave-like fashion: the increase was accompanied by a decrease. In some parts of the curves obtained the PFC numbers increased or decreased 2 to 7 times within 4 hours. A marked increase in PFC numbers in the controls and in animals treated with both cytostatics occurred at 60, 72--76, 84--88 h of the immune response. It is suggested that methotrexate and vinblastine do not prevent recruitment of precursor cells into PFC and consequently the number of PFC increases. The decrease in PFC numbers under the influence of both cytostatics presumably results from "unbalanced growth".