<i>M. tuberculosis</i> induced alterations in Siglecs’ expression on neutrophils predicts susceptibility to infection

Abstract The Presence of neutrophils in tuberculosis (TB) lung lesions is associated with bacterial growth. Despite being potent microbicidal cells, why neutrophils in TB lesions fail to control bacterial replication is poorly understood. By infecting mice with a hypervirulent replication reporter Mycobacterium tuberculosis (Mtb) W-Beijing Strain HN878, we found elevated neutrophils containing bacteria, associated with host susceptibility to infection. Phenotypic characterization of neutrophils from infected lungs revealed a downregulation of canonical neutrophil marker Siglec E (SigE) with concomitant upregulation of Siglec H (SigH), a marker generally used to define plasmacytoid dendritic cells. SigH expression on lung neutrophils increased with disease progression and predicts susceptibility to TB. Importantly, these non-conventional Ly6G+SigH+ neutrophils harbored more replicating bacteria compared to Ly6G+SigH-SigE+ lung neutrophils. In-vitro infection of naïve bone marrow neutrophils showed enhanced SigH expression with increased infectivity, and this was dependent on glycolysis and fatty acid metabolism. Treatment of immunocompetent mice with neutralizing antibodies for SigH reduced live cell bacterial burden, neutrophil infiltration, restricted bacterial replication and increased neutrophil expression of SigE. Further, SigH neutralized mice also showed elevated T cell numbers, indicating protective immunity. Collectively, our data suggests a model where Mtb induces SigH expression on neutrophils to survive within them, as a potential immune evasion strategy. Our future studies will determine the functional significance of this alteration in Siglecs on neutrophils and its role in TB pathogenesis. R56 AI148239-01A1 and R21AI16359 (sub-award) from NIH/NIAID toDr. Bibhuti B Mishra