Lipocalin 2 modulates dendritic cell activity and shapes immunity to influenza in a microbiome dependent manner.

Martin L Watzenboeck,Gabriel M Richard,Gijs A Versteeg,Asma Farhat,Barbara Drobits,Therese Lederer,Karin Lakovits,Louis Boon,Anastasiya Hladik,Anna-Dorothea Gorki,Birgit Strobl,Sylvia Knapp,Philipp Starkl,Federica Quattrone,Sophie Zahalka,Mehul Suthar

doi:10.1371/journal.ppat.1009487

Abstract

Lipocalin 2 (LCN2) is a secreted glycoprotein with roles in multiple biological processes. It contributes to host defense by interference with bacterial iron uptake and exerts immunomodulatory functions in various diseases. Here, we aimed to characterize the function of LCN2 in lung macrophages and dendritic cells (DCs) using Lcn2-/- mice. Transcriptome analysis revealed strong LCN2-related effects in CD103+ DCs during homeostasis, with differential regulation of antigen processing and presentation and antiviral immunity pathways. We next validated the relevance of LCN2 in a mouse model of influenza infection, wherein LCN2 protected from excessive weight loss and improved survival. LCN2-deficiency was associated with enlarged mediastinal lymph nodes and increased lung T cell numbers, indicating a dysregulated immune response to influenza infection. Depletion of CD8+ T cells equalized weight loss between WT and Lcn2-/- mice, proving that LCN2 protects from excessive disease morbidity by dampening CD8+ T cell responses. In vivo T cell chimerism and in vitro T cell proliferation assays indicated that improved antigen processing by CD103+ DCs, rather than T cell intrinsic effects of LCN2, contribute to the exacerbated T cell response. Considering the antibacterial potential of LCN2 and that commensal microbes can modulate antiviral immune responses, we speculated that LCN2 might cause the observed influenza phenotype via the microbiome. Comparing the lung and gut microbiome of WT and Lcn2-/- mice by 16S rRNA gene sequencing, we observed profound effects of LCN2 on gut microbial composition. Interestingly, antibiotic treatment or co-housing of WT and Lcn2-/- mice prior to influenza infection equalized lung CD8+ T cell counts, suggesting that the LCN2-related effects are mediated by the microbiome. In summary, our results highlight a novel regulatory function of LCN2 in the modulation of antiviral immunity.

Highlights

Lipocalin 2 (LCN2) is a 25-kDa secreted glycoprotein involved in a variety of biological processes, including immune responses, iron homeostasis and metabolism [1,2,3]
We explored the precise effects of LCN2 on cellular lung immunity, and discovered that LCN2 markedly impacted homeostatic expression of pulmonary dendritic cell (DC) genes related to anti-influenza immunity
We found the presence of LCN2 associated with dampened DC functions, preventing exuberant T cell activation during influenza infection

Summary

Introduction

Lipocalin 2 (LCN2) is a 25-kDa secreted glycoprotein involved in a variety of biological processes, including immune responses, iron homeostasis and metabolism [1,2,3]. Acting as scavenger of bacterial siderophores, LCN2 is known as host defense molecule with potent antibacterial activity against siderophore-dependent bacteria, such as Escherichia coli and Klebsiella pneumonia [4,5] In line with this function, LCN2 is highly expressed in barrier tissues exposed to microorganisms including the lungs [6] and further induced upon Toll-like receptor (TLR) stimulation [4]. Our group could previously show that LCN2 deactivates lung macrophages and worsens disease outcome from pneumonia caused by the siderophore-independent pathogen Streptococcus pneumoniae [10] These studies highlight effects of LCN2 on myeloid cell function and plasticity, with important consequences in various infectious and non-infectious diseases. Since the microbiome can strongly influence many aspects of the host immune system [11], this could be a major relay mediating LCN2-related immunomodulatory effects

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