Comparison of allergenic activity of rFel d 1 and PreS fusion proteins in the CD203c basophil activation test. Blood cells from 7 patients with cat allergy (Table 1, nos. 4, 7, 13, 14, 17, 18, and 23) were exposed to PBS (unstim.), anti-IgE, and serial dilutions (10-0.01 μg/mL) of rFel d 1, PreS-2xP1, PreS-2xP5, or PreS-P1-P5 (x-axes). CD203c expression on basophils was determined by means of FACS analysis. CD203c upregulation is displayed as the stimulation index (y-axes).