LAUSR

A vaccine is an important method to control schistosomiasis. Molecules related to lung-stage schistosomulum are considered potential vaccine candidates. We previously showed that glyceraldehyde-3-phosphate dehydrogenase (GAPDH) and cathepsin L3 (CL3) displayed differential expression in the lung-stage schistosomula of Schistosoma japonicum cocultured with host cells. In the present study, we prepared the two proteins and detected the protective effects of Sj GAPDH by immunizing mice with this protein alone and in combination with Sj CL3 with or without Freund’s adjuvant. Then, we investigated the possible mechanisms underlying S. japonicum infection. The results showed that vaccination of adjuvanted Sj GAPDH decreased the worm burden (37.8%) and egg load (38.1%), and the combination of adjuvanted Sj GAPDH and Sj CL3 further decreased the worm burden (65.6%) and egg load (70.9%) during Schistosoma japonicum infection. However, the immunization of a combination of adjuvant-free Sj GAPDH and Sj CL3 displayed a lower protective effect (< 15%) than those of the adjuvanted Sj CL3, the adjuvanted Sj GAPDH, and a combination of adjuvanted Sj GAPDH and Sj CL3. Flow cytometric results showed that the frequency of regulatory T cells (Tregs) was lower ( P < 0.05) in the group with adjuvanted Sj GAPDH and Sj CL3 (2.61%) than the remaining groups. The enzyme-linked immunosorbent assay (ELISA) results indicated that except for the uninfected and infected control groups, the remaining groups displayed a Th1-type shift in immune responses. These results showed the immunization of Sj GAPDH resulted in partial protection (approximately 38%); inoculation with a combination of Sj CL3 and Sj GAPDH in Freund’s adjuvant resulted in a high immunoprotective effect (> 65%) against Schistosoma japonicum infection in mice, which was possibly caused by the reduced percentage of Tregs and a Th1-type shift in immune responses; and Sj CL3 has no adjuvant-like effect, dissimilar to Sm CL3.