Mice were immunised s.c. in the scruff with 100 μg of ovalbumin (OVA) alone or conjugated to 20 nm, 40 nm, 100 nm, 200 nm or 1000 nm particles. 14 days later, serum was tested by ELISA for anti-OVA-IgG2c (A) and anti-OVA-IgG1 (B). Data show the mean (−) absorbance (405 nm) at a dilution of 1 in 200 with the five experimental animals per group (′) ***p < 0.001 comparing to the PBS group. To assess functional responses, C57BL/6 mice were immunised s.c. with 50 μg of hemagglutinin (HA) alone, conjugated to 40 or 200 nm particles, or emulsified with complete Freund's adjuvant (CFA). Weight changes were then monitored following intranasal infection with 300 PFU of influenza A virus (WSN) (C). Data shows the mean of five experimental animals per group ± standard deviation ***p < 0.001 comparing 200 nm group to 40 nm group.