Maturing Neutrophils of Lower Density Associate with Thrombocytopenia in Puumala Orthohantavirus-Caused Hemorrhagic Fever with Renal Syndrome - Human samples

Puumala orthohantavirus-caused hemorrhagic fever with renal syndrome (PUUV-HFRS) is characterized by significant neutrophil activation. Neutrophils, the most abundant immune cells in circulation, are equipped to respond rapidly to infections and exhibit a notable heterogeneity. This study aims to identify and characterize different neutrophil subsets in the circulation of PUUV-HFRS patients, focusing on low-density granulocytes (LDGs) and normal density polymorphonuclear cells (PMNs). The study finds that PMNs show activation of antiviral pathways, while circulating LDGs increase following acute PUUV-HFRS. Additionally, PUUV-associated LDGs, primarily immature, likely reflect increased bone marrow neutrophil production. Notably, the frequency of LDGs and a "left shift" in blood are associated with the extent of thrombocytopenia, a hallmark of severe HFRS, suggesting a role for maturing neutrophils in disease pathogenesis. Unlike COVID-19 associated LDGs, PUUV LDGs did not exhibit significant immunosuppressive ability, indicating inherent biological differences in LDG responses based on the causative virus or infection kinetics. RNA sequencing was performed on neutrophils isolated from four cohorts: healthy control PMNs, PUUV-infected PMNs, PUUV-infected CD16- LDGs, and PUUV-infected CD16+ LDGs. The RNA sequencing and subsequent bioinformatics analysis were conducted by the Biomedicum Functional Genomics Unit at the Helsinki Institute of Life Science and Biocenter Finland at the University of Helsinki.