FIG. 4.

Recognition of E. histolytica surface lectin by baboon serum IgG antibodies as assessed by an IFA following intranasal vaccination with the synthetic peptide vaccine (1,600-μg dose). Sera collected from vaccinated baboons (▴) at 28 days and prepared as serial dilutions from 1/8 to 1/128 demonstrated positive reactions to whole trophozoites as determined by an IFA (P, <0.001 for each dilution compared to control baboon sera [○]). (Means are represented by solid and dotted lines, respectively.) In addition, serial dilutions of immune baboon sera demonstrated a stepwise decrease in IFA-measured fluorescence intensity (P, <0.01 for 1/8 to 1/16 and 1/16 to 1/32). Importantly, 100% of study baboons receiving this vaccine dose had positive serum responses as determined by an IFA (P, <0.001 compared to control baboons). Control baboon sera did not show a positive IFA result at any dilution compared to results from IFA studies without serum present (data not shown).