The aim of this study was to evaluate the ex vivo and in vivo studies immune potential of α-and κ-casein. Ex vivo, naïve mouse splenocytes were stimulated with α-or κ-casein. After 120 h of culture, the proliferation index (PI), determined by 3-(4,5 dimethylthiazol-2yl)-2,5-diphenyl tetrazolium bromide (MTT) assay and carboxyfluorescein diacetate N-succinimidyl ester (CFSE) staining, did not vary for either antigen, suggesting similar ex vivo immunogenic potential of both casein fractions. In vivo, BALB/ccmdb mice were sensitized with α-or κ-casein and then gavaged with primary antigen. Mice immunized with α-casein had higher levels of IgG (2 16.33) and IgA (2 10.22) in serum at the end of the experiment compared with mice immunized with κ-casein (2 15 and 2 9.3 for IgG and IgA, respectively). The use of α-casein for mouse immunization and ex vivo lymphocyte stimulation resulted in higher concentrations of secreted cytokines (IL-4, IL-10) compared with κ-casein stimulation. This is consistent with increasing regulatory T cell (Treg) lymphocyte populations, independent of the antigen used for stimulation. In summary, the immunogenic potential of α-and κ-casein was similar. Humoral and cellular immune responses confirmed their strong, independent potential to induce B and T cells. We propose that the lymphocyte proliferation index be used as an initial screening for protein immunogenicity.