title: Processing and major histocompatibility complex class II presentation of Legionella pneumophila antigens by infected macrophages.
abstract: To better understand interactions between the intracellular pathogen Legionella pneumophila and macrophages (Mphis), host and bacterial determinants important for presentation of antigens on major histocompatibility complex class II molecules (MHC-II) were investigated. It was determined that immune CD4 T-cell responses to murine bone marrow-derived Mphis (BMphis) infected with wild-type L. pneumophila were higher than the responses to avirulent dotA mutant bacteria. Although this enhanced response by immune T cells required modulation of vacuole transport mediated by the Dot/Icm system, it did not require intracellular replication of L. pneumophila. Intracellular cytokine staining identified a population of immune CD4 T cells that produced gamma interferon upon incubation with BMphis infected with wild-type L. pneumophila that did not respond to Mphi infection with dotA mutant bacteria. Endocytic processing was required for presentation of L. pneumophila antigens on MHC-II as determined by a defect in CD4 T-cell responses when the pH of BMphi endosomes was neutralized with chloroquine. Investigation of MHC-II presentation of antigens by BMphis infected with L. pneumophila icmR, icmW, and icmS mutants indicated that these mutants have an intermediate presentation phenotype relative to those of wild-type and dotA mutant bacteria. In addition, it was found that antigens from dot and icm mutants are presented earlier than antigens from wild-type L. pneumophila. Although immune CD4 T-cell responses to proteins secreted by the L. pneumophila Lsp system were not detected, it was found that the Lsp system is important for priming L. pneumophila-specific T cells in vivo. These data indicate that optimal antigen processing and MHC-II presentation to immune CD4 T cells involves synthesis of L. pneumophila proteins in an endoplasmic reticulum-derived compartment followed by transport to lysosomes.
authors.affiliation: Section of Microbial Pathogenesis, Boyer Center for Molecular Medicine, Yale University School of Medicine, 295 Congress Ave., New Haven, CT 06536, USA.
authors.forename: Annie
authors.initials: A
authors.lastname: Neild
authors.forename: Takahiro
authors.initials: T
authors.lastname: Murata
authors.forename: Craig R
authors.initials: CR
authors.lastname: Roy
mesh_terms: D000818:Animals; D017951:Antigen Presentation; D000942:Antigens, Bacterial / Q000378:metabolism*; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology; D004705:Endocytosis; D000949:Histocompatibility Antigens Class II / Q000502:physiology*; D007371:Interferon-gamma / Q000096:biosynthesis; D016952:Legionella pneumophila / Q000276:immunology*; D008213:Lymphocyte Activation; D008247:Lysosomes / Q000378:metabolism; D008264:Macrophages / Q000276:immunology* / Q000382:microbiology; D051379:Mice; D014617:Vacuoles / Q000382:microbiology
chemical_list: D000942:Antigens, Bacterial; D000949:Histocompatibility Antigens Class II; D007371:Interferon-gamma