title: IFN-γ-induced priming maintains long-term strain-transcending immunity against blood-stage Plasmodium chabaudi malaria.
abstract: The mechanism by which protective immunity to Plasmodium is lost in the absence of continued exposure to this parasite has yet to be fully elucidated. It has been recently shown that IFN-γ produced during human and murine acute malaria primes the immune response to TLR agonists. In this study, we investigated whether IFN-γ-induced priming is important to maintain long-term protective immunity against Plasmodium chabaudi AS malaria. On day 60 postinfection, C57BL/6 mice still had chronic parasitemia and efficiently controlled homologous and heterologous (AJ strain) challenge. The spleens of chronic mice showed augmented numbers of effector/effector memory (TEM) CD4(+) cells, which is associated with increased levels of IFN-γ-induced priming (i.e., high expression of IFN-inducible genes and TLR hyperresponsiveness). After parasite elimination, IFN-γ-induced priming was no longer detected and protective immunity to heterologous challenge was mostly lost with >70% mortality. Spontaneously cured mice had high serum levels of parasite-specific IgG, but effector T/TEM cell numbers, parasite-driven CD4(+) T cell proliferation, and IFN-γ production were similar to noninfected controls. Remarkably, the priming of cured mice with low doses of IFN-γ rescued TLR hyperresponsiveness and the capacity to control heterologous challenge, increasing the TEM cell population and restoring the CD4(+) T cell responses to parasites. Contribution of TLR signaling to the CD4(+) T cell responses in chronic mice was supported by data obtained in mice lacking the MyD88 adaptor. These results indicate that IFN-γ-induced priming is required to maintain protective immunity against P. chabaudi and aid in establishing the molecular basis of strain-transcending immunity in human malaria.
authors.affiliation: Departamento de Imunologia, Instituto de Ciências Biomédicas, Universidade de São Paulo, 05508-000 São Paulo, Brazil.
authors.forename: Henrique Borges
authors.initials: HB
authors.lastname: da Silva
authors.forename: Erika Machado
authors.initials: EM
authors.lastname: de Salles
authors.forename: Raquel Hoffmann
authors.initials: RH
authors.lastname: Panatieri
authors.forename: Silvia Beatriz
authors.initials: SB
authors.lastname: Boscardin
authors.forename: Sérgio Marcelo
authors.initials: SM
authors.lastname: Rodríguez-Málaga
authors.forename: José Maria
authors.initials: JM
authors.lastname: Alvarez
authors.forename: Maria Regina
authors.initials: MR
authors.lastname: D'Império Lima
mesh_terms: D000818:Animals; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology* / Q000378:metabolism; D049109:Cell Proliferation; D005260:Female; D007074:Immunoglobulin G / Q000097:blood; D007371:Interferon-gamma / Q000276:immunology*; D018655:Lymphocyte Count; D008288:Malaria / Q000097:blood / Q000276:immunology* / Q000469:parasitology; D051379:Mice; D008810:Mice, Inbred C57BL; D018345:Mice, Knockout; D053594:Myeloid Differentiation Factor 88 / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D018512:Parasitemia / Q000276:immunology / Q000469:parasitology; D016788:Plasmodium chabaudi / Q000276:immunology*; D015398:Signal Transduction / Q000276:immunology
chemical_list: D007074:Immunoglobulin G; C507780:Myd88 protein, mouse; D053594:Myeloid Differentiation Factor 88; D007371:Interferon-gamma