Cooperation between Monocyte-Derived Cells and Lymphoid Cells in the Acute Response to a Bacterial Lung Pathogen.
Legionella pneumophila is the causative agent of Legionnaires' disease, a potentially fatal lung infection. Alveolar macrophages support intracellular replication of L. pneumophila, however the contributions of other immune cell types to bacterial killing during infection are unclear. Here, we used recently described methods to characterise the major inflammatory cells in lung after acute respiratory infection of mice with L. pneumophila. We observed that the numbers of alveolar macrophages rapidly decreased after infection coincident with a rapid infiltration of the lung by monocyte-derived cells (MC), which, together with neutrophils, became the dominant inflammatory cells associated with the bacteria. Using mice in which the ability of MC to infiltrate tissues is impaired it was found that MC were required for bacterial clearance and were the major source of IL12. IL12 was needed to induce IFNγ production by lymphoid cells including NK cells, memory T cells, NKT cells and γδ T cells. Memory T cells that produced IFNγ appeared to be circulating effector/memory T cells that infiltrated the lung after infection. IFNγ production by memory T cells was stimulated in an antigen-independent fashion and could effectively clear bacteria from the lung indicating that memory T cells are an important contributor to innate bacterial defence. We also determined that a major function of IFNγ was to stimulate bactericidal activity of MC. On the other hand, neutrophils did not require IFNγ to kill bacteria and alveolar macrophages remained poorly bactericidal even in the presence of IFNγ. This work has revealed a cooperative innate immune circuit between lymphoid cells and MC that combats acute L. pneumophila infection and defines a specific role for IFNγ in anti-bacterial immunity.
Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Melbourne, Victoria, Australia.
Andrew S
AS
Brown
Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia.
Chao
C
Yang
Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia.
Ka Yee
KY
Fung
Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia.
Annabell
A
Bachem
Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Melbourne, Victoria, Australia.
Dorothée
D
Bourges
Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia.
Sammy
S
Bedoui
Department of Microbiology and Immunology, University of Melbourne at the Peter Doherty Institute for Infection and Immunity, Melbourne, Victoria, Australia.
Elizabeth L
EL
Hartland
Department of Biochemistry and Molecular Biology, Bio21 Molecular Science and Biotechnology Institute, University of Melbourne, Melbourne, Victoria, Australia.
Ian R
IR
van Driel
D019264:Adoptive Transfer; D000818:Animals; D004195:Disease Models, Animal; D005434:Flow Cytometry; D007113:Immunity, Innate / Q000276:immunology; D007371:Interferon-gamma / Q000276:immunology*; D016952:Legionella pneumophila / Q000276:immunology; D007877:Legionnaires' Disease / Q000276:immunology*; D008214:Lymphocytes / Q000276:immunology*; D051379:Mice; D008810:Mice, Inbred C57BL; D008817:Mice, Mutant Strains; D009000:Monocytes / Q000276:immunology*; D016133:Polymerase Chain Reaction
D007371:Interferon-gamma