Mechanism of cellular suppression induced by oral tilorone treatment of mice.

Specific-pathogen-free B6D2 F1 hybrid mice were treated orally with tilorone hydrochloride (100 mg/kg of body weight per day) and infected with sublethal doses of Listeria monocytogenes, Salmonella enteritidis, Mycobacterium bovis (BCG Pasteur), or M. tuberculosis Erdman. Daily tilorone treatment inhibited the cell-mediated response to all of the intracellular parasites, and most of the mice succumbed to the challenge. Tilorone suppressed delayed hypersensitivity responses to the microbial sensitins as well as to sheep erythrocytes. However, humoral responses (immediate hypersensitivity reactions) were stimulated. The types of growth curves obtained in the tilorone-treated mice were quite different from those observed in T-cell-depleted mice and tended to resemble those seen in sublethally irradiated (400 rads) animals. Leukocyte counts were depressed 10-fold by daily tilorone treatment. Both monocyte and granulocyte (but not large-lymphocyte) counts were depressed. There was an initial drop in small-lymphocyte counts with a later recovery phase. Tilorone treatment reduced the granulomatous response within the Salmonella-infected liver, suggesting that the drug interferes with the mobilization of the mononuclear defenses within the normal host.