SPP1 and COVID-19: The relative proportions of cell clusters revealed that SPP1 stimulation at 200 ng/mL, equivalent to plasma concentration of severe COVID-19, was associated with a significantly increased neutrophil proportion (Figure 6, B and C) with a shift from the normally dominant CD10+ (MME+) neutrophil phenotype to a CD274+ (PD-L1+) neutrophil phenotype.