Studies on the Mechanism of Action of Methotrexate and Cyclophosphamide on Contact Sensitivity in the Guinea Pig

Abstract

The contact agents used were 2-phenyl-4-ethoxy-methylene-5-oxazolone and picryl chloride. The effects of the drug regimes starting on different days after sensitization was studied. Inhibition of the development of sensitivity was found consistently with methotrexate if the course was started 2 or 4 days after sensitization, and with cyclophosphamide if the course was started 2 days after sensitization. Drug regimes started after the fourth day gave inconsistent results. In some cases skin test sites showed reactions 3-4 days after the drug was withdrawn. Guinea-pigs which had been maintained on the drug for 8 days were still capable of being passively sensitized by the transfusion of lymphoid cells from sensitive donors. Methotrexate caused no diminution in passive sensitivity, though cyclophosphamide caused some diminution of reactivity which was probably nonspecific.