Search

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.

Mice immunized with soluble adult worm antigen (SWAP) in combination with cholera toxin (CT) displayed significantly larger numbers of IgG1, IgM and IgA secreting cells in the spleen and in the lungs as compared to mice which had received SWAP only. The ratio of SWAP-specific IgG1 to IgG2a antibody-secreting spleen cells was also significantly higher in the SWAP-CT group. Analysis of cytokine responses revealed that SWAP-stimulated spleen and lung cells from the SWAP-CT group produced lower levels of IFN-gamma but higher levels of IL-4 and IL-5 as compared to cells from the SWAP group. These findings indicate that intranasal administration of SWAP-CT induces a Th2 cell response in the spleen and in the lungs. Our findings also suggest that CT was responsible for induction of this Th2 cell response, since intranasal administration of SWAP alone induced a Th1 type response in the spleen and in the lungs.

A comparison has been made of a new serological method, thin layer immunoassay (TIA), and an established method, enzyme-linked immunosorbent assay (ELISA), in the detection and quantification of antibodies in schistosomiasis. Using sera from known S. haematobium and S. mansoni cases, the performance of the two tests was almost identical; 95.6% positive for TIA and 96.4% by ELISA. TIA however produced a small number of false positives with sera from other helminth infections whereas ELISA gave none. There was excellent correlation between the tests in the quantification of anti-S. haematobium antibodies, both in human cases and in infected baboons. TIA has the advantage of being extremely simple to perform, but has the disadvantage of requiring a higher concentration of antigens.

The effect of the immunomodulating substance cyclosporin A (CyA) has been evaluated in mice infected with Schistosoma mansoni. Administration of CyA at the time of infection or during the schistosomulum stage resulted in failure of the larvae to develop into adult worms. However, a serological response was noted. Administration of CyA during the establishment of the adult worm stage resulted in a reduction of the worm burden as compared to non-treated mice. The established worm pairs, however, seemed to be sterile since no eggs were demonstrated in the liver. Infection of mice with cercariae which had been exposed to CyA in vitro resulted in only a slight reduction of the worm burden for the highest concentration of CyA tested (100 micrograms/ml). The results of the study show that administration of CyA in vivo affects the host-parasite relationship in favour of the host.