Mahmoud BAHGAT1, Katerina
FRANCKLOW2, Mike DOENHOFF2, Reda RAMZY3,
YONG Long Li4 and Andreas RUPPEL1
1 Department
of Tropical Hygiene, University of Heidelberg, Im Neuenheimer
Feld 324, 69120, Heidelberg, Germany
2School of Biological Sciences, University of Wales,
Bangor, UK
3Research and Training Center on Vectors of Diseases,
Ain Shams University, Cairo, Egypt
4Department of Parasitology, Tongji Medical College,
Huazhong Science and Technology University, Wuhan, P. R. China
Cercarial secretions (CSs) from different species of Schistosoma and from Trichobilharzia ocellata showed a 30 kDa digestion band in gelatin gel electrophoresis. This band corresponds to the cercarial elastase (CE). Using a colorimetric substrate, the specific activity of serine protease was always 2-3 folds higher in CSs from T. ocellata compared to S. mansoni. The enzyme showed optimal activity at pH 10, is Ca++-dependent (inhibition with EDTA), trypsin like (inhibition with anti-pain), and is a serine proteinase (inhibition with PMSF). Also minute concentration (8 nM) of aprotinin, a potent inhibitor for serine proteases, abolished 90 % of the activity in CSs of both parasites. IgG measurement by ELISA showed a high degree of cross-reaction among CSs from different species with both Chinese and African infection sera. In western blots, using infection sera from humans, heavily infected mice as well as rabbits, the reactiviy towards the 30 kDa protein fraction was, however, absent. This suggests the absence of an antibody response against the enzyme following natural infection. Moreover, when sections from infected snails (Biomphalaria and Bulinus) were analyzed by immunofluorescence using the same infection sera, only the tegument of the developing cercariae was recognized, but the acetabular glands were not reactive. In contrast, when sections were tested with antisera against CE from either S. mansoni or S. haematobium, reactivity was exclusively concentrated in the preacetabular glands of the cercariae. Sections from S.japonicum-infected snails (Oncomelania) did not cross-react with these antisera. In conclusion, although CE is essential in the penetration process of schistosomes, it does not apparently induce an antibody response following natural infection. MB was supported by a scholarship from the German Academic Research Council (DAAD), who also supports the collaboration between RR, YLL and AR.
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created 21/12/00
