Vaccination of mice with a 30kDa Schistosoma antigen with and without human adjuvant induces high protection against S. mansoni infection A.M. Attallah 1 *, M.M. Abdel Aziz 2 , A.T. Abbas 2 , K.A. Elbakry 2,3 and M.M. El-Sharabasy 3 1 Biotechnology Research Center, PO Box 14, 23 July Street, Industrial Zone, New Damietta City 34517, Egypt: 2 Gastro-enterology Center, Mansoura University, Mansoura 35111, Egypt: 3 Faculty of Science – Damietta, Mansoura University, New Damietta 34517, Egypt Abstract A 30 kDa antigen was characterized as a hydrophobic polypeptide containing 16 amino acids and evaluated as a potential candidate vaccine against infection by Schistosoma mansoni. CD1 albino mice immunized at 0, 14, and 21 days with 25 or 50 mg of the 30 kDa antigen per mouse with and without alum developed high levels of IgG antibodies (predominantly IgG2a and IgG2b isotypes). When immunized mice were infected with 200 S. mansoni cercariae, the highest protection levels (61% and 65% reduction in worm burden in two separate experiments) were obtained using the 50-mg antigen without alum adjuvant. The granuloma size decreased to 10%, a non-significant level in mice immunized using alum adjuvant. The results demonstrate the ability of the 30 kDa antigen with and without alum adjuvant to protect mice against S. mansoni infection. Introduction Over the past decade, several promising candidate vaccine antigens for Schistosoma mansoni have been identified and characterized. Six antigens, selected by WHO for protection studies in two independent laboratories, showed resistance against challenge infec- tion but the stated goal of consistent induction of 40% protection or better was not reached with any of these antigen formulations, underlining the difficulty in characterizing and delivering an effective vaccine against schistosomes (Bergquist & Colley, 1998). Various approaches have been used to identify vaccine candi- dates, e.g. the development of monoclonal antibodies capable of conferring resistance (Capron et al., 1987; Harn et al., 1992). Attallah et al. (1999a) produced an IgG2a anti- S. mansoni monoclonal antibody, designated BRL4 mAb, which has been shown to reduce worm loads at 51.6%, 41.9% and 53.8% protection levels in three separate passive transfer experiments. The target epitope of the protective BRL4 mAb was identified in three different Schistosoma antigenic preparations of cercariae (CAP), adult worms (SWAP), and eggs (SEA) at 74 kDa molecular weight protein antigen (Attallah et al., 1998). The 74 kDa antigen has been shown to protect mice of different strains and to modulate the host immune system (Attallah et al., 1999b). However, a target reactive epitope of the BRL4 mAb was also identified at a lower molecular weight antigen of 30 kDa in urine of infected individuals and a-chymotrypsin and trypsin digestion products of the affinity purified 74 kDa antigen (Attallah et al., 1998). In the present study, we investigated the protection induced against S. mansoni infection by immunization of mice with the lower molecular weight antigen, 30 kDa, with and without human adjuvant, alum. Materials and methods Host animals, infection and perfusion Female outbred CD1 albino mice (about 20 g in weight) were used for immunization experiments. A Puerto Rican *Fax: þ20 57 401889 E-mail: amattallah@hotmail.com Journal of Helminthology (2004) 78, 189–194 DOI: 10.1079/JOH2004241