title: Subcellular antigen location influences T-cell activation during acute infection with Toxoplasma gondii.
abstract: Effective control of the intracellular protozoan parasite Toxoplasma gondii depends on the activation of antigen-specific CD8(+) T-cells that manage acute disease and prevent recrudescence during chronic infection. T-cell activation in turn, requires presentation of parasite antigens by MHC-I molecules on the surface of antigen presenting cells. CD8(+) T-cell epitopes have been defined for several T. gondii proteins, but it is unclear how these antigens enter into the presentation pathway. We have exploited the well-characterized model antigen ovalbumin (OVA) to investigate the ability of parasite proteins to enter the MHC-I presentation pathway, by engineering recombinant expression in various organelles. CD8(+) T-cell activation was assayed using 'B3Z' reporter cells in vitro, or adoptively-transferred OVA-specific 'OT-I' CD8(+) T-cells in vivo. As expected, OVA secreted into the parasitophorous vacuole strongly stimulated antigen-presenting cells. Lower levels of activation were observed using glycophosphatidyl inositol (GPI) anchored OVA associated with (or shed from) the parasite surface. Little CD8(+) T-cell activation was detected using parasites expressing intracellular OVA in the cytosol, mitochondrion, or inner membrane complex (IMC). These results indicate that effective presentation of parasite proteins to CD8(+) T-cells is a consequence of active protein secretion by T. gondii and escape from the parasitophorous vacuole, rather than degradation of phagocytosed parasites or parasite products.
authors.affiliation: Department of Biology, University of Pennsylvania, Philadelphia, Pennsylvania, United States of America.
authors.forename: Beth
authors.initials: B
authors.lastname: Gregg
authors.forename: Florence
authors.initials: F
authors.lastname: Dzierszinski
authors.forename: Elia
authors.initials: E
authors.lastname: Tait
authors.forename: Kimberly A
authors.initials: KA
authors.lastname: Jordan
authors.forename: Christopher A
authors.initials: CA
authors.lastname: Hunter
authors.forename: David S
authors.initials: DS
authors.lastname: Roos
mesh_terms: D019264:Adoptive Transfer; D000818:Animals; D000938:Antigen-Presenting Cells / Q000276:immunology; D000953:Antigens, Protozoan / Q000276:immunology*; D015153:Blotting, Western; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology*; D002478:Cells, Cultured; D005260:Female; D005455:Fluorescent Antibody Technique; D006801:Humans; D008213:Lymphocyte Activation / Q000276:immunology*; D008285:Major Histocompatibility Complex / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D010047:Ovalbumin / Q000502:physiology; D013347:Subcellular Fractions; D014122:Toxoplasma / Q000235:genetics / Q000276:immunology; D014123:Toxoplasmosis / Q000276:immunology* / Q000378:metabolism / Q000469:parasitology*; D014617:Vacuoles / Q000276:immunology* / Q000469:parasitology
chemical_list: D000953:Antigens, Protozoan; D010047:Ovalbumin