Effect of leukodepleted RBC supernatants on the neutrophil response to FMLP. Locomotory activity of neutrophils incubated in the upper compartment of the chemotaxis chamber with medium and exposed in the lower compartment for 45 minutes to medium (Nil) and 10 nM FMLP (FMLP) was compared with locomotory activity of cells incubated in the upper compartment with RBC supernatant (1: 1 × 10⁵, vol/vol dilution; SUP^RBCs + FMLP) or leukodepleted RBC supernatant (1:1 × 10⁵, vol/vol dilution; SUP^WBC + FMLP) and exposed in the lower compartment to 10 nM FMLP. Results are expressed as mean ± 1 SD of 3 experiments with neutrophils from different donors.