ADHERENCE-INHIBITORY INTESTINAL IgA ANTIBODY RESPONSE ELICITED IN BABOONS BY A SYNTHETIC INTRANASAL LECTIN-BASED AMEBIASIS SUBUNIT VACCINE. [Infect Immun] Journal article

We designed a amebiasis subunit vaccine that is constructed by using the four peptide epitopes of the galactose-inhibitable lectin heavy subunit that were recognized by intestinal sIgA antibodies from immune human subjects. These epitopes are contained within amino acids 758 to 1134 of the lectin heavy subunit of the heavy subunit, designated LC3. Baboons (Papio annibus) are natural hosts for Entamoeba histolytica; naturally infected baboons raised in captivity possess serum IgA antibodies to the same four LC3 epitopes as humans. Uninfected, seronegative baboons received four intranasal (IN) immunizations at 7 day interval with the synthetic peptide vaccine (400 microg, 800 microg, or 1600 microg per nostril) with cholera toxin (20 microg) as adjuvant. By ELISA, all 6 baboons immunized at each dose of the peptide vaccine elicited anti-peptide serum IgA, IgG and intestinal IgA antibody responses at 28 days, 7 days after the last immunization (p<0.01 for each compared to CT control). The peptide vaccine elicited serum IgG and intestinal IgA antibodies that recognized purified recombinant LC3 protein (p<0.008 and p = 0.02 respectively) and native lectin protein (p<0.01). In addition, IFA to whole trophozoites (p<0.01) and Western Blot analysis confirmed that serum IgG antibodies from vaccinated baboons recognized native lectin protein on the surface of axenic E. histolytica trophozoites or from solubilized ameba. All four synthetic peptides were immunogenic; the vaccine exhibited a dose and time dependent response as determined by ELISA OD readings for serum and intestinal production (p<0.02 for anti-peptide or anti-lectin antibodies respectively). As a positive control, IN immunization with purified recombinant LC3 protein with CT as adjuvant elicited a serum anti-LC3 IgA and IgG antibody response (p = 0.05 and p <0.0001 respectively); however, no intestinal anti-LC3 IgA antibody response was observed (p = 0.4). Of interest, serum IgA and IgG antibodies elicited by the recombinant LC3 vaccine did not recognize any of the four putatively protective LC3 peptide epitopes. Both serum and fecal antibodies elicited by the peptide vaccine exhibited neutralizing activity, as determined by their dose dependent inhibition of the galactose-specific adherence of E. histolytica trophozoites to Chinese Hamster Ovary cells in vitro, (p<0.001 for each compared to control). In summary, a lectin-based intranasal polylysine-linked synthetic peptide vaccine was effective in eliciting a adherence-inhibitory, intestinal anti-lectin IgA antibody response in baboons. Future studies in the baboon model will determine vaccine efficacy against asymptomatic E. histolytica intestinal infection.

Infect Immun