HBsAg-specific immunoglobulin A (IgA) responses after intranasal (IN) immunization (small volume). BALB/c mice (n = 5–10) were immunized by IN inhalation of 10 µg of HBsAg with 1, 10, or 50 µg cholera toxin (CT) and/or CpG-containing oligodeoxynucleotides (CpG) as adjuvants in a volume of 20 µl Mice were boosted at 4 and 8 weeks. Each bar represents the group geometric mean of the ELISA end-point dilution titer (GMT) for HBsAg-specific IgA antibodies (anti-HBs IgA GMT) in lung and gut washes, feces, saliva, and vaginal washes collected 4 weeks after final immunization. Titers were defined as the highest sample dilution resulting in an absorbance value two times that of non-immune sample, with a cut-off value of 0.05. HBsAg, purified hepatitis B surface antigen.