All four CPEs were immunogenic for both mouse strains tested. All sera showed positive results when reacting to the homologous protein extract coated on the ELISA plate. There were no significant intergroup differences in serum reactivity of CPE sensitized C57BL/6 mice (Fig 4A). However, significant differences in reactivity of sensitized Balb/c mice were observed (Fig 4B). Animals sensitized with CPE-BB2ßME and those sensitized with CPE-BB presented significantly higher mean polyisotypic IgG antibody titers (p<0.01 and p<0.001, respectively) than those sensitized with CPE-TB/HCl and animals sensitized with CPE-BB presented significantly higher mean antibody titers (p<0.05) than those sensitized with CPE-SB (Fig 4B).