title: Mechanism of interleukin 12-mediated toxicities during experimental viral infections: role of tumor necrosis factor and glucocorticoids.
abstract: Interleukin 12 (IL-12) doses in excess of 100 ng/d have been shown to induce profound immunotoxicities in mice infected with lymphocytic choriomeningitis virus (LCMV). These immunotoxicities are characterized by almost complete inhibition of virus-induced CD8+ T cell expansion and CTL activation, and up to 2 log increases in viral replication. They are accompanied by induction of serum tumor necrosis factor (TNF). The studies presented here were undertaken to characterize mechanisms for the IL-12-induced toxicities and to examine expression and function of TNF in this context. Several physiological changes were induced in IL-12-treated uninfected and dramatically elevated in IL-12-treated virus-infected mice. IL-12 induced (a) decreases in body weights, > 10% in uninfected and > 20% in LCMV-infected mice; (b) elevation of circulating glucocorticoid levels to > 10 micrograms/dl in uninfected and > 20 micrograms/dl in infected mice; and (c) decreases in thymic mass, > 30% in uninfected and up to 95% in infected mice. These changes are known to be associated with circulating TNF. Northern blot and in situ hybridization analyses demonstrated that IL-12 induced TNF-alpha expression and that LCMV infection synergized with IL-12 for induction of this factor. Antibodies neutralizing TNF reversed all of the IL-12-induced toxicities in LCMV-infected mice including the immunotoxicities against CD8+ T cells and anti-viral defenses. The TNF-mediated immunotoxicities appeared to result from an induced cellular sensitivity to the factor, as splenic leukocytes and CD8+ T cell subsets isolated from LCMV-infected mice were more sensitive to TNF-mediated cytotoxicity in culture than were equivalent populations prepared from uninfected mice. Experiments with the glucocorticoid type II receptor antagonist, RU486, demonstrated that endogenous glucocorticoids were secondary intermediaries in IL-12-induced thymic atrophy. Studies in IL-2-deficient mice showed that the synergism was dependent upon endogenous IL-2. The results delineate a unique mechanism of TNF-mediated toxicity. In addition, they have significant implications concerning potential detrimental consequences of in vivo TNF induction and of IL-12 administration for protective anti-viral responses.
authors.affiliation: Division of Biology and Medicine, Brown University, Providence, Rhode Island 02912.
authors.forename: J S
authors.initials: JS
authors.lastname: Orange
authors.forename: T P
authors.initials: TP
authors.lastname: Salazar-Mather
authors.forename: S M
authors.initials: SM
authors.lastname: Opal
authors.forename: R L
authors.initials: RL
authors.lastname: Spencer
authors.forename: A H
authors.initials: AH
authors.lastname: Miller
authors.forename: B S
authors.initials: BS
authors.lastname: McEwen
authors.forename: C A
authors.initials: CA
authors.lastname: Biron
mesh_terms: D000818:Animals; D018414:CD8-Positive T-Lymphocytes / Q000502:physiology; D003345:Corticosterone / Q000097:blood; D005938:Glucocorticoids / Q000502:physiology*; D018664:Interleukin-12 / Q000633:toxicity*; D007376:Interleukin-2 / Q000502:physiology; D008216:Lymphocytic Choriomeningitis / Q000276:immunology*; D008297:Male; D051379:Mice; D008810:Mice, Inbred C57BL; D015735:Mifepristone / Q000494:pharmacology; D014409:Tumor Necrosis Factor-alpha / Q000502:physiology*
chemical_list: D005938:Glucocorticoids; D007376:Interleukin-2; D014409:Tumor Necrosis Factor-alpha; D018664:Interleukin-12; D015735:Mifepristone; D003345:Corticosterone