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.