title: IL-12 administered in vivo to young and aged mice. Discrepancy between the effects on tumor growth in vivo and cytotoxic T lymphocyte generation ex vivo: dependence on IFN-gamma.
abstract: Because IL-12 restores allogeneic cytotoxic T lymphocyte (CTL) activity by T cells of aged mice in vitro, we initially assessed whether IL-12 could overcome age-related deficits when given to aged mice in vivo. Growth of P815(H-2(d)) was enhanced in aged compared with young BALB/c (H-2(d)) mice and tumor growth was curtailed by IL-12 in both age groups. Unexpectedly, secondary CTL stimulated ex vivo with P815 were reduced in IL-12-treated mice compared with controls. Primary CTL generated ex vivo across MHC differences in IL-12 treated BALB/c and C57BL/6 young mice were reduced by 90-99%, were dose- and time-dependent, and were associated with reduced allo-stimulated NK-like activity and [3H]thymidine incorporation. IFN-gamma was elevated in sera and in supernatants from allo-stimulated cultures from IL-12-treated mice, while IL-4 was reduced in such supernatants, suggesting that, despite reduced CTL, IL-12 was associated with increased Th1- and reduced Th2-type cytokine production. IL-12 also induced splenomegaly, primarily due to increased numbers of cells lacking markers of mature T, B and NK cells, or macrophages, or polymorphonuclear leukocyte morphology. IFN-gamma mutant mice exhibited reduced splenic enlargement in response to IL-12, suggesting that the splenomegaly was due, in part, to IFN-gamma production. However, reduced CTL generation was not due entirely to dilution of CTL precursor cells because spleen cellularity and size increased 3-fold while CTL activity decreased 10- to 100-fold, and CTL generation normalized to CD8(+) T effector cells was still significantly reduced in IL-12-treated mice. Interestingly, purified CD4(+) and CD8(+) T cells from IL-12-treated normal mice exhibited greater proliferative and cytolytic activities respectively compared with controls. Thus, effector T cells in IL-12-treated mice were not impaired, but exhibited augmented responsiveness, suggesting that IL-12 induced complex interactions among spleen cell populations and that these effects, in part, are mediated by IFN-gamma.
authors.affiliation: Laboratory of Cellular Immunology (HFM-518), Center for Biologics Evaluation Research, Food and Drug Administration, Bethesda, MD 20892, USA.
authors.forename: J A
authors.initials: JA
authors.lastname: Horvath-Arcidiacono
authors.forename: H S
authors.initials: HS
authors.lastname: Mostowski
authors.forename: E T
authors.initials: ET
authors.lastname: Bloom
mesh_terms: D000276:Adjuvants, Immunologic / Q000008:administration & dosage; D000367:Age Factors; D000818:Animals; D002469:Cell Separation; D005260:Female; D006084:Graft Rejection / Q000276:immunology*; D007371:Interferon-gamma / Q000096:biosynthesis / Q000276:immunology*; D018664:Interleukin-12 / Q000008:administration & dosage* / Q000276:immunology*; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D009368:Neoplasm Transplantation; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology*; D014407:Tumor Cells, Cultured
chemical_list: D000276:Adjuvants, Immunologic; D018664:Interleukin-12; D007371:Interferon-gamma