Immune response after immunization with ovalbumin loaded polystyrene particles. C57BL/6 mice were immunized once with 5 μg soluble ovalbumin (ova), or ovalbumin-coated polystyrene particles of 24 nm (24p), 60 nm (60p), 93 nm (93p), 220 nm (220p), or 340 nm diameter (340p) carrying 5 μg ovalbumin, either by intramuscular, footpad, subcutaneous or intraperitoneal injection. Two weeks after immunization ovalbumin specific IgG levels were determined luminometrically from 1:10000 dilutions of plasma by ELISA (A). To compare different amounts of protein, mice were immunized once by intramuscular injection with 50 ng, 500 ng, or 5000 ng of ovalbumin, either as soluble protein or coated on 93 nm polystyrene particles, and IgG1 (B) and IgG2c antibody titers (C) were analyzed in 1:100 dilution of plasma two weeks after immunization. Statistically significant differences compared to naïve mice or mice immunized with the respective amount of soluble ovalbumin are indicated by * or #, respectively (P < 0.05, Student-Newman-Keuls method). The graphs show mean values of RLU/s (relative light units per second) and standard errors of the means of 4 (B, C) or 8 mice per group (A); data was acquired in two independent experiments.