3.4. ORF8-specific IgG response
ELISA assay was used to determine the ORF8-specific antibody titers in the BALB/c mice. As shown in Fig. 3A, the ORF8-specific IgG titers of the PBS and ORF8 groups were very low upon the three immunizations, suggesting the intrinsically low immunogenicity of ORF8. The ORF8-specific IgG titers of the ORF8-CRM, ORF8-PEG and ORF8/AL groups were all low at the first dose (day 7). The second (day 14) and the third doses (day 21) progressively enhanced the ORF8-specific IgG titers of the three groups. In particular, the ORF8-specific IgG titer of the ORF8-PEG group (2.6×104) was higher than those of the ORF8-CRM group (1.1×104) (P<0.05) and ORF8/AL group (1.8×104) (P<0.05) at the third dose (day 21). This indicated that the adjuvant effect of administration with aluminum adjuvant was lower than self-conjugation with 8-arm PEG, and higher than that of conjugation with CRM197.