Suppression of immune and hemopoietic cellular responses by methisazone.

The antiviral drug methisazone (N-methylisatin beta-thiosemicarbazone) was tested for its effect on immune responses to sheep erythrocytes and on hemopoietic colony-forming cell (granulocyte-macrophage progenitor cell) responses to complete Freund's adjuvant in mice. Suppressive activity was demonstrated in both systems, the immune system being more readily and more consistently susceptible. Evidence is presented which suggests that the insoluble particulate form of the drug has both stimulatory and suppressive effects on the colony-forming cell system, whereas the soluble form is only suppressive. Methisazone increased the mortality from ectromelia in adjuvant-treated animals.