Inhibition of delayed hypersensitivity by metronidazole and misonidazole.

The effect on cell-mediated immunity of two hypoxic cell radiosensitizers, metronidazole and misonidazole, was examined. Immunocompetence was assayed by measuring delayed hypersensitivity reactions in mice sensitized on the abdomen with 2,4-dinitro-1-fluorobenzene (DNFB) and subsequently challenged on the ears with DNFB. Single and fractionated treatments with misonidazole or metronidazole were found to suppress delayed hypersensitivity reactions to DNFB. This finding is in agreement with other data in the literature which show that many imidazoles, including nitroimidazoles, inhibit aspects of the cell-mediated immune response in animals and man. The potential immunosuppressive effects of nitroheterocyclic radiosensitizers should be considered when these agents are evaluated in the laboratory or used in the clinic.