title: IL-12 is required to maintain a Th1 response during Leishmania major infection.
abstract: IL-12 initiates Th1 cell development and cell-mediated immunity, but whether IL-12 contributes to the maintenance of a Th1 response is unclear. To address this question, we infected IL-12 p40-/- C57BL/6 mice with Leishmania major, an intracellular protozoan parasite controlled by a cell-mediated immune response, and simultaneously administered IL-12. Whereas untreated p40-/- mice developed an uncontrolled infection, p40-/- mice treated with IL-12 for the first 2 or 4 wk of infection developed a Th1 response and resolved their lesions. However, the induction of this protective Th1 cell response by IL-12 treatment was not associated with long term immunity. We observed that on rechallenge in the absence of IL-12, the mice exhibited a susceptible phenotype. In addition, without rechallenge, lesions in the IL-12-treated p40-/- mice developed several weeks after cessation of IL-12 treatment. In both cases, disease was associated with the loss of a Th1 response and the development of a Th2 response. Our observations are not limited to the C57BL/6 strain, because IL-12 treatment was also unable to provide lasting protection to p40-/- BALB/c mice. Finally, we found that although Th1 cells from healed wild-type C57BL/6 mice adoptively transferred protection to L. major-infected RAG-/- mice, they were unable to protect p40-/- mice. In conclusion, these studies provide the first demonstration that IL-12 is required not only to initiate Th1 cell development but also throughout infection to maintain a Th1 cell response and resistance to L. major.
authors.affiliation: Department of Pathobiology, University of Pennsylvania School of Veterinary Medicine, Philadelphia, PA 19104, USA.
authors.forename: A Y
authors.initials: AY
authors.lastname: Park
authors.forename: B D
authors.initials: BD
authors.lastname: Hondowicz
authors.forename: P
authors.initials: P
authors.lastname: Scott
mesh_terms: D019264:Adoptive Transfer; D000818:Animals; D004334:Drug Administration Schedule; D005260:Female; D016654:Genes, RAG-1 / Q000276:immunology; D007113:Immunity, Innate; D015552:Injections, Intralesional; D018664:Interleukin-12 / Q000008:administration & dosage / Q000172:deficiency / Q000235:genetics / Q000502:physiology*; D018320:Leishmania major / Q000276:immunology*; D016773:Leishmaniasis, Cutaneous / Q000235:genetics / Q000276:immunology* / Q000517:prevention & control; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D018417:Th1 Cells / Q000276:immunology* / Q000378:metabolism / Q000637:transplantation
chemical_list: D018664:Interleukin-12