Immunogenicity of DIII-C-AP205. Groups of female BALB/c mice (n = 4) were immunized subcutaneously three times (days 0, 14, and 28, arrows) with either 50 μg of DIII-C-AP205 or a mixture of the corresponding amounts of free DIII-C protein (13.6 μg) and free AP205 VLPs (36.4 μg) in the absence of adjuvants. DIII-C-specific IgG antibody titers were measured at the indicated time points. The dashed line indicates the detection limit. Shown are group means ± SEM.