Female Balb-c mice, 6-8 weeks old (Charles River, Netherlands), were housed in groups of 5 and maintained in the animal facility of Utrecht University with a 12 h day and night schedule, while food and water were ad libitum. The experiments were approved by the Ethical Committee for Animal Experimentation of Utrecht University. Mice (5 per group) were intramuscularly (i.m.) immunized twice with 2-week intervals. Mice received 100 ll of different formulations (Table 1 ) divided over two batches of 50 ll which were injected in each of the hind leg muscles. Before each immunization and 2 weeks after the last immunization, the mice were bled by cheek puncture and then sacrificed by inhalation of excess CO 2 . Individual serum samples were separated from blood cells and coagulated proteins by centrifugation for 5 min at 14,0009g and 4°C, and stored at -20°C.