Immunological cross reactivity between Schistosoma mansoni and cholera toxin

Intranasal administration of schistosome antigens in combination with appropriate adjuvant may be an effective route for immunization against schistosomes, since the lungs represent an important site of elimination of schistosomulae. Our previous studies have shown that in mice intranasal administration of cholera toxin (CT) before infection with Schistosoma mansoni results in an enhancement of the worm burden in comparison to nontreated infected animals. In the present study, it was shown that mice treated intranasally with CT displayed high numbers of schistosome-reactive IgM-secreting cells in the spleen as well as high levels of schistosome-reactive serum IgM antibodies, whereas no significant immunological response against two other antigens, ovalbumin (OVA) or keyhole limpet haemocyanin (KLH) was noted. Sera from mice treated intranasally with CT recognized a 22 kDA antigen on SWAP blots. This band was not demonstrable after absorption of the sera with SWAP. These findings indicate a possible cross reactivity between cholera toxin and schistosome antigens. Further analysis by Western blot revealed that a 22 kDa antigen was detected on CT blots by sera from mice and humans infected with S. mansoni. This band was not demonstrable after absorption of the mouse or the human sera with CT. The 22 kDa cross reactive antigen was heat-stable. The antibodies against the 22 kDa antigen were only found within the IgM class but not within other Ig isotypes. Our findings also indicate that the 22 kDa antigen detected by anti-S. mansoni antibodies represents the A1 fragment of the cholera toxin.