title: Attachment ligands of viable Toxoplasma gondii induce soluble immunosuppressive factors in human monocytes.
abstract: Previous studies have demonstrated that surface antigen proteins, in particular SAG-1, of Toxoplasma gondii are important to this parasite as attachment ligands for the host cell. An in vitro assay was developed to test whether these ligands and other secretory proteins are involved in the immune response of human cells to toxoplasma. Human monocytes were infected with tachyzoites in the presence of antiparasite antibodies, and their effect on mitogen-induced lymphoproliferation was examined. The presence of antibody to either parasite-excreted proteins (MIC-1 and MIC-2) or surface proteins (SAG-1 and SAG-2) during infection neutralized the marked decrease seen in mitogen-induced lymphoproliferation in the presence of infected monocytes. Conversely, antibodies to other secreted proteins (ROP-1) and cytoplasmic molecules had no effect on parasite-induced, monocyte-mediated downregulation. Fluorescence microscope analysis detected microneme and surface antigen proteins on the monocyte cell surface during infection. These results suggest that microneme and surface antigen proteins trigger monocytes to downregulate mitogen-induced lymphoproliferation.
authors.affiliation: Departments of Microbiology, Dartmouth Medical School, Lebanon, New Hampshire, USA. Jacqueline.Channon@Dartmouth.Edu
authors.forename: J Y
authors.initials: JY
authors.lastname: Channon
authors.forename: E I
authors.initials: EI
authors.lastname: Suh
authors.forename: R M
authors.initials: RM
authors.lastname: Seguin
authors.forename: L H
authors.initials: LH
authors.lastname: Kasper
mesh_terms: D000818:Animals; D000953:Antigens, Protozoan / Q000378:metabolism; D002448:Cell Adhesion / Q000276:immunology; D002462:Cell Membrane / Q000276:immunology / Q000469:parasitology; D006801:Humans; D066298:In Vitro Techniques; D008024:Ligands; D008213:Lymphocyte Activation; D009000:Monocytes / Q000276:immunology* / Q000469:parasitology; D015800:Protozoan Proteins / Q000276:immunology* / Q000378:metabolism; D012995:Solubility; D013491:Suppressor Factors, Immunologic / Q000096:biosynthesis*; D014122:Toxoplasma / Q000276:immunology* / Q000472:pathogenicity*; D016781:Toxoplasmosis, Cerebral / Q000209:etiology / Q000276:immunology
chemical_list: D000953:Antigens, Protozoan; D008024:Ligands; D015800:Protozoan Proteins; C047168:SAG1 antigen, Toxoplasma; D013491:Suppressor Factors, Immunologic