The effect of febrile temperatures on biologic actions of interferons: abrogation of suppression of delayed-type hypersensitivity and antibody production.

Interferons (IFN) have a complex immunoregulatory effect on all cells of the immune system. In most cases in which IFN had an enhancing effect, the suggested mechanism was inhibition of the generation or activity of suppressor cells. In the present study, we examined the effect of IFN on suppression of the delayed-type hypersensitivity (DTH) response. Suppression was induced with a low antigen dose of sheep erythrocytes (SRBC), and IFN was found to abrogate both the suppressed state and the transferability of this state. Cyclophosphamide had the same effect. However, the in vitro generation of suppressor cells was not altered by the addition of IFN to the culture medium at a normal temperature (37 degrees C). To reconcile the disparity between the successful anti-suppressive action of IFN in vivo compared with its failure in vitro, we considered the possibility that the pyrogenic action of IFN in vivo might create the optimal thermal environment for its anti-suppressive action. Indeed, when IFN was then tested in vitro at a febrile temperature (39.3 degrees C), it completely blocked the generation of suppressor cells. On the other hand, once suppressor cells were generated at 37 degrees C, IFN had no effect on their ability to suppress a fresh culture either at 37 degrees C or at 39.3 degrees C. IFN also had no effect on the generation of helper cells at either temperature, but help was greatly enhanced by high temperature alone. In vivo, we found our IFN preparation to be pyrogenic and observed that an anti-pyretic drug given before and during antigen stimulation abrogated the anti-suppressive effect of IFN. We suggest, therefore, that the febrile state induced by IFN promotes its action on suppressor cells.