Cooperation between Monocyte-Derived Cells and Lymphoid Cells in the Acute Response to a Bacterial Lung Pathogen

Andrew S. Brown, Chao Yang, Ka Yee Fung, Annabell Bachem, Dorothée Bourges, Sammy Bedoui, Elizabeth L. Hartland, Ian R. van Driel

Research output: Contribution to journalArticleResearchpeer-review

30 Citations (Scopus)


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.

Original languageEnglish
Article numbere1005691
Number of pages20
JournalPLoS Pathogens
Issue number6
Publication statusPublished - 14 Jun 2016
Externally publishedYes

Cite this