To determine the contribution of specific neutrophil subsets to the pathogenesis of acute COVID-19, flow cytometry was used to identify immature (CD15+CD16+CD115–CXCR2–), mature (CD16hiCD62LhiCXCR2hiCXCR4lo), senescent (CD11bhiCXCR2loCD62LloCXCR4hi), and degranulated (CD11b+CD18+Gr-1int) neutrophils, and LDNs (mouse LDNs are ARG1+CD15+CD33+CD101–CXCR4+) (41) in the peripheral blood of middle-aged mice infected with 5000 PFU of SARS2-N501YMA30 (gating strategies are shown in Supplemental Figure 4A) (41). Here, CSF1R is linked to COVID-19.