title: NK cells help to induce CD8(+)-T-cell immunity against Toxoplasma gondii in the absence of CD4(+) T cells.
abstract: CD8(+) T-cell immunity plays an important role in protection against intracellular infections. Earlier studies have shown that CD4(+) T-cell help was needed for launching in vivo CD8(+) T-cell activity against these pathogens and tumors. However, recently CD4(+) T-cell-independent CD8 responses during several microbial infections including those with Toxoplasma gondii have been described, although the mechanism is not understood. We now demonstrate that, in the absence of CD4(+) T cells, T. gondii-infected mice exhibit an extended NK cell response, which is mediated by continued interleukin-12 (IL-12) secretion. This prolonged NK cell response is critical for priming parasite-specific CD8(+) T-cell immunity. Depletion of NK cells inhibited the generation of CD8(+) T-cell immunity in CD4(-/-) mice. Similarly neutralization of IL-12 reduces NK cell numbers in infected animals and leads to the down-regulation of CD8(+) T-cell immunity against T. gondii. Adoptive transfer of NK cells into the IL-12-depleted animals restored their CD8(+) T-cell immune response, and animals exhibited reduced mortality. NK cell gamma interferon was essential for cytotoxic T-lymphocyte priming. Our studies for the first time demonstrate that, in the absence of CD4(+) T cells, NK cells can play an important role in induction of primary CD8(+) T-cell immunity against an intracellular infection. These observations have therapeutic implications for immunocompromised individuals, including those with human immunodeficiency virus infection.
authors.affiliation: Department of Microbiology, Immunology, and Parasitology, Louisiana State University Health Sciences Center, 1901 Perdido Street, New Orleans, LA 70112, USA.
authors.forename: Crescent L
authors.initials: CL
authors.lastname: Combe
authors.forename: Tyler J
authors.initials: TJ
authors.lastname: Curiel
authors.forename: Magali M
authors.initials: MM
authors.lastname: Moretto
authors.forename: Imtiaz A
authors.initials: IA
authors.lastname: Khan
mesh_terms: D019264:Adoptive Transfer; D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D005260:Female; D018664:Interleukin-12 / Q000097:blood; D007694:Killer Cells, Natural / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D016176:T-Lymphocyte Subsets / Q000276:immunology; D013997:Time Factors; D014122:Toxoplasma / Q000276:immunology*; D014123:Toxoplasmosis / Q000276:immunology
chemical_list: D018664:Interleukin-12