title: CD8(+)-T-cell immunity against Toxoplasma gondii can be induced but not maintained in mice lacking conventional CD4(+) T cells.
abstract: T-cell immunity is critical for survival of hosts infected with Toxoplasma gondii. Among the cells in the T-cell population, CD8(+) T cells are considered the major effector cells against this parasite. It is believed that CD4(+) T cells may be crucial for induction of the CD8(+)-T-cell response against T. gondii. In the present study, CD4(-/-) mice were used to evaluate the role of conventional CD4(+) T cells in the immune response against T. gondii infection. CD4(-/-) mice infected with T. gondii exhibited lower gamma interferon (IFN-gamma) messages in the majority of their tissues. As a result, mortality due to a hyperinflammatory response was prevented in these animals. Interestingly, T. gondii infection induced a normal antigen-specific CD8(+)-T-cell immune response in CD4(-/-) mice. No difference in generation of precursor cytotoxic T lymphocytes (pCTL) or in IFN-gamma production by the CD8(+)-T-cell populations from the knockout and wild-type animals was observed. However, the mutant mice were not able to sustain CD8(+)-T-cell immunity. At 180 days after infection, the CD8(+)-T-cell response in the knockout mice was depressed, as determined by pCTL and IFN-gamma assays. Loss of CD8(+)-T-cell immunity at this time was confirmed by adoptive transfer experiments. Purified CD8(+) T cells from CD4(-/-) donors that had been immunized 180 days earlier failed to protect the recipient mice against a lethal infection. Our study demonstrated that although CD8(+)-T-cell immunity can be induced in the absence of conventional CD4(+) T cells, it cannot be maintained without such cells.
authors.affiliation: Department of Medicine, Dartmouth Medical School, Lebanon, New Hampshire 03756, USA.
authors.forename: Lori
authors.initials: L
authors.lastname: Casciotti
authors.forename: Kenneth H
authors.initials: KH
authors.lastname: Ely
authors.forename: Martha E
authors.initials: ME
authors.lastname: Williams
authors.forename: Imtiaz A
authors.initials: IA
authors.lastname: Khan
mesh_terms: D000284:Administration, Oral; D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology*; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D007371:Interferon-gamma / Q000096:biosynthesis; D007421:Intestine, Small / Q000473:pathology; D008099:Liver / Q000473:pathology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D013602:T-Lymphocytes, Cytotoxic / Q000276:immunology; D014122:Toxoplasma / Q000276:immunology; D014123:Toxoplasmosis / Q000276:immunology* / Q000469:parasitology / Q000473:pathology
chemical_list: D007371:Interferon-gamma