Clodronate is not protective in lethal viral encephalitis despite substantially reducing inflammatory monocyte infiltration in the CNS

Alanna G Spiteri; Caryn van Vreden; Thomas M Ashhurst; Paula Niewold; Nicholas J C King

doi:10.3389/fimmu.2023.1203561

Clodronate is not protective in lethal viral encephalitis despite substantially reducing inflammatory monocyte infiltration in the CNS

Front Immunol. 2023 Jul 20:14:1203561. doi: 10.3389/fimmu.2023.1203561. eCollection 2023.

Authors

Alanna G Spiteri^{1

2}, Caryn van Vreden^{1

2}, Thomas M Ashhurst³, Paula Niewold^{1

2

4}, Nicholas J C King^{1

2

3

5

6}

Affiliations

¹ Viral Immunopathology Laboratory, Infection, Immunity and Inflammation Research Theme, School of Medical Sciences, Faculty of Medicine and Health, The University of Sydney, Sydney, NSW, Australia.
² Charles Perkins Centre, The University of Sydney, Sydney, NSW, Australia.
³ Sydney Cytometry, The University of Sydney and Centenary Institute, Sydney, NSW, Australia.
⁴ Department of Infectious Diseases, Leiden University Medical Centre, Leiden, Netherlands.
⁵ The University of Sydney Institute for Infectious Diseases, The University of Sydney, Sydney, NSW, Australia.
⁶ The University of Sydney Nano Institute, The University of Sydney, Sydney, NSW, Australia.

Abstract

Bone marrow (BM)-derived monocytes induce inflammation and tissue damage in a range of pathologies. In particular, in a mouse model of West Nile virus (WNV) encephalitis (WNE), nitric oxide-producing, Ly6C^hi inflammatory monocytes from the BM are recruited to the central nervous system (CNS) and contribute to lethal immune pathology. Reducing the migration of these cells into the CNS using monoclonal antibody blockade, immune-modifying particles or CSF-1R inhibitors reduces neuroinflammation, improving survival and/or clinical outcomes. Macrophages can also be targeted more broadly by administration of clodronate-encapsulated liposomes, which induce apoptosis in phagocytes. In this study, clodronate reduced the inflammatory infiltrate by 70% in WNE, however, surprisingly, this had no effect on disease outcome. More detailed analysis demonstrated a compensatory increase in neutrophils and enhanced activation status of microglia in the brain. In addition, we observed increased numbers of Ly6C^hi BM monocytes with an increased proliferative capacity and expression of SCA-1 and CD16/32, potentially indicating output of immature cells from the BM. Once in the brain, these cells were more phagocytic and had a reduced expression of antigen-presenting molecules. Lastly, we show that clodronate also reduces non-myeloid cells in the spleen and BM, as well as ablating red blood cells and their proliferation. These factors likely impeded the therapeutic potential of clodronate in WNE. Thus, while clodronate provides an excellent system to deplete macrophages in the body, it has larger and broader effects on the phagocytic and non-phagocytic system, which must be considered in the interpretation of data.

Keywords: CNS infection; bone marrow monopoiesis; clodronate; macrophage depletion; monocyte-derived cells; monocyte-mediated inflammation; neuroinflammation; virus-induced encephalitis.

Publication types

Research Support, Non-U.S. Gov't

MeSH terms

Animals
Central Nervous System / pathology
Clodronic Acid / pharmacology
Encephalitis, Viral* / pathology
Macrophages
Mice
Monocytes
West Nile Fever*

Substances

Clodronic Acid

Grants and funding

NK was supported by a National Health and Medical Research Council Project Grant 1088242 and the Merridew Foundation. AS was supported by the Australian Government Research Training Stipend Scholarship and The University of Sydney Postgraduate Merit Award.