AUTHOR=Hlavaty Sabina I. , Chang Yu-Mei , Orth Rachel P. , Goulian Mark , Planet Paul J. , Thamm Douglas H. , Punt Jennifer A. , Garden Oliver A. 

TITLE=Bacterial Killing Activity of Polymorphonuclear Myeloid-Derived Suppressor Cells Isolated From Tumor-Bearing Dogs

JOURNAL=Frontiers in Immunology

VOLUME=10

YEAR=2019

URL=https://www.frontiersin.org/journals/immunology/articles/10.3389/fimmu.2019.02371

DOI=10.3389/fimmu.2019.02371

ISSN=1664-3224

ABSTRACT=<p>Polymorphonuclear myeloid-derived suppressor cells (PMN-MDSCs) are implicated in the progression and outcome of a variety of pathological states, from cancer to infection. Our previous work has identified three antimicrobial peptides differentially expressed by PMN-MDSCs compared to conventional neutrophils isolated from dogs, mice, and human patients with cancer. We therefore hypothesized that PMN-MDSCs in dogs with cancer possess antimicrobial activity. In the current work, we observed that exposure of PMN-MDSCs to Gram-negative bacteria (<italic>Escherichia coli</italic>) increased the expression of reactive oxygen species by the PMN-MDSCs, indicating that they are capable of initiating an anti-microbial response. Electron microscopy revealed that the PMN-MDSCs phagocytosed Gram-negative and Gram-positive (<italic>Staphylococcus aureus</italic>) bacterial species. Lysis of bacteria within some of the PMN-MDSCs suggested bactericidal activity, which was confirmed by the recovery of significantly lower numbers of bacteria of both species following exposure to PMN-MDSCs isolated from tumor-bearing dogs. Our data therefore indicate that PMN-MDSCs isolated from dogs with cancer, in common with PMNs, have phagocytic and bactericidal activity. This nexus of immunosuppressive and antimicrobial activity reveals a hitherto unrecognized function of MDSCs.</p>