The short‐term effects of 4‐nitroquinoline 1‐oxide on the immune response in mice

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Abstract
The short‐term effects of the carcinogen 4‐Nitroquinoline 1‐oxide (NQO) on the number of plaque‐forming spleen cells (PFC) after immunization with sheep erythrocytes have been tested in (C57BL × IF) mice. The number of PFC was reduced in the NQO‐treated mice and this reduction was greater with higher doses of carcinogen. The times of appearance of the peaks of the 19S and 7S antibody response do not appear to be altered. Two non‐carcinogenic analogues of NQO, chloroquinoline‐N‐oxide (CQO) and nitropyridine N‐oxide (NPO) had no such immunodepressive effect. NQO had its maximum immunosuppressive effect when administered two days after the antigen, at the time of maximum division of the antibody‐producing cells. Reconstitution experiments suggest that the rapidly dividing bone‐marrow cells are most affected by NQO and there is no evidence that the thymus cells are affected. Correspondingly, no depression of cell‐mediated immunity by NQO was found, either in rejection time of skin allografts or of the graft‐versus‐host reaction.These findings are discussed in relation to suggestions that immune depression by chemical carcinogens is of aetiological significance.