PolyP suppresses total hemolytic activity. rRBCs were incubated with 4.5% serum in the presence of increasing concentrations of P₁ (●) or polyP_>1000 (○). Values were normalized to baseline lysis in the absence of phosphate. Curves were fitted to a nonlinear regression inhibitory dose–response model to determine IC₅₀ for P₁ and polyP, shown by dotted lines. Results are representative of 3 experiments, each performed in triplicate.