Migration of eosinophils into nitrocellulose micropore filters (5-μm pore size) toward various concentrations of soluble chemoattractants. Various concentrations of SN (0.1 pmol/L to 10 μmol/L), SP (0.01 pmol/L to 1 μmol/L), IL-8 (1 fmol/L to 0.1 μmol/L) (left panel), RANTES (1 fmol/L to 0.1 μmol/L), fMLP (0.01 pmol/L to 1 μmol/L), or β-endorphin (0.01 pmol/L to 1 μmol/L) (right panel) were placed in the lower wells of a modified Boyden chamber. RPMI 1640/0.5% BSA served as control to determine random migration. Thereafter 50 μL of human eosinophils at 1 × 10⁶ cells/mL were added to the upper wells and were allowed to migrate for 60 minutes at 37°C (humidified atmosphere; 5% CO₂). After fixing and staining of the filters migration depth was quantified microscopically. Data are expressed as mean ± SEM of the “Chemotaxis Index,” which is the ratio between the distance cells migrate toward test substances and that toward control medium. n = 6. Statistical analyses: Mann-Whitney U-test after Kruskal Wallis analysis of variance (P < .01); n.s., not significant; *, P < .05; **, P < .01.