title: Lack of IL-15 results in the suboptimal priming of CD4+ T cell response against an intracellular parasite.
abstract: IFN-gamma-producing CD4+ T cells, although important for protection against acute Toxoplasma gondii infection, can cause gut pathology, which may prove to be detrimental for host survival. Here we show that mice lacking IL-15 gene develop a down-regulated IFN-gamma-producing CD4+ T cell response against the parasite, which leads to a reduction in gut necrosis and increased level of survival against infection. Moreover, transfer of immune CD4+ T cells from WT to IL-15-/- mice reversed inhibition of gut pathology and caused mortality equivalent to levels of parental WT mice. Down-regulated CD4+ T cell response in the absence of IL-15, manifested as reduced antigen-specific proliferation, was due to defective priming of the T cell subset by dendritic cells (DCs) of these animals. When stimulated with antigen-pulsed DCs from WT mice, CD4+ T cells from IL-15-/- mice were primed optimally, and robust proliferation of these cells was observed. A defect in the DCs of knockout mice was further confirmed by their reduced ability to produce IL-12 upon stimulation with Toxoplasma lysate antigen. Addition of exogenous IL-15 to DC cultures from knockout mice led to increased IL-12 production by these cells and restored their ability to prime an optimal parasite-specific CD4+ T cell response. To our knowledge, this is the first demonstration of the role of IL-15 in the development of CD4+ T cell immunity against an intracellular pathogen. Furthermore, based on these observations, targeting of IL-15 should have a beneficial effect on individuals suffering from CD4+ T cell-mediated autoimmune diseases.
authors.affiliation: Department of Microbiology, Parasitology, and Immunology, Louisiana State University Health Sciences Center, New Orleans, LA 70112, USA.
authors.forename: Crescent L
authors.initials: CL
authors.lastname: Combe
authors.forename: Magali M
authors.initials: MM
authors.lastname: Moretto
authors.forename: Joseph D
authors.initials: JD
authors.lastname: Schwartzman
authors.forename: Jason P
authors.initials: JP
authors.lastname: Gigley
authors.forename: David J
authors.initials: DJ
authors.lastname: Bzik
authors.forename: Imtiaz A
authors.initials: IA
authors.lastname: Khan
mesh_terms: D019264:Adoptive Transfer; D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D003713:Dendritic Cells / Q000276:immunology; D005260:Female; D006801:Humans; D007371:Interferon-gamma / Q000096:biosynthesis; D018664:Interleukin-12 / Q000096:biosynthesis; D019409:Interleukin-15 / Q000172:deficiency* / Q000235:genetics; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D014122:Toxoplasma / Q000276:immunology* / Q000302:isolation & purification; D014124:Toxoplasmosis, Animal / Q000276:immunology* / Q000469:parasitology / Q000473:pathology
chemical_list: D019409:Interleukin-15; D018664:Interleukin-12; D007371:Interferon-gamma