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Schistosoma mansoni: anomalous immunogenic properties of a 27 kDa larval serine protease associated with protective immunity

Published online by Cambridge University Press:  01 September 1997

H. Y. DARANI
Affiliation:
School of Biological Sciences, University of Wales, Bangor, Deiniol Road, Bangor, Gwynedd LL57 2UW, UK
R. H. C. CURTIS
Affiliation:
School of Biological Sciences, University of Wales, Bangor, Deiniol Road, Bangor, Gwynedd LL57 2UW, UK
C. McNEICE
Affiliation:
School of Biological Sciences, University of Wales, Bangor, Deiniol Road, Bangor, Gwynedd LL57 2UW, UK
H. P. PRICE
Affiliation:
School of Biological Sciences, University of Wales, Bangor, Deiniol Road, Bangor, Gwynedd LL57 2UW, UK
J. R. SAYERS
Affiliation:
Present address: Rothamsted Experimental Station, Harpenden, Hertfordshire, AL5 2JQ. School of Biological Sciences, University of Wales, Bangor, Deiniol Road, Bangor, Gwynedd LL57 2UW, UK
M. J. DOENHOFF
Affiliation:
Present address: Department of Medicine and Pharmacology, Royal Hallamshire Hospital, Sheffield S10 2JF. School of Biological Sciences, University of Wales, Bangor, Deiniol Road, Bangor, Gwynedd LL57 2UW, UK

Abstract

A cationic Schistosoma mansoni cercarial antigen was shown to be a serine protease as it was capable of hydrolysing N-acetyl-dl-phenylalanine β-naphthyl ester (NAPBNE) after precipitation by immunoelectrophoresis, and this reaction was modulated by the serine protease inhibitors phenylmethanesulfonyl fluoride (PMSF) and diisopropylfluorophosphate (DFP). The antigen in the immunoprecipitin arcs could also be radio-isotope labelled with tritiated DFP. The peptidolytic enzyme identified in immunoelectrophoresis with polyspecific sera and radio-isotope labelled with tritiated DFP had a relative molecular size of approximately 27 kDa in sodium dodecyl sulphate polyacrylamide gel electrophoresis (SDS–PAGE), and evidence obtained after partial purification, SDS–PAGE and immunoblotting supported this size estimate for the enzyme. A rabbit antiserum raised against the peptidolytic antigen reacted against a doublet of antigens at 27/28 kDa in immunoelectrophoresis arcs and against an antigen of 60 kDa in Western immunoblots of crude cercarial homogenate. However, the latter serum precipitated the cationic antigen in immunoelectrophoresed cercarial homogenates only after pre-incubation of the homogenates with PMSF. Fractions containing the partially purified protease also degraded radio-isotope labelled human IgG. The reactivity of a range of polyspecific and monospecific rabbit antisera in Western blots with larval extracts indicated that antibody responses against the 27/28 kDa doublet may be modulated. When immunized with material which contained the 27 kDa enzyme as a major constituent, and which was secreted by S. mansoni cercariae during transformation, only 5 of 16 mice produced antibody to this antigen that was detectable in Western blots. The 5 antibody ‘responder’ mice were significantly (P<0·001) protected against challenge with a percutaneous infection of S. mansoni cercariae compared with a group of mice also immunized with CTF, but which had not produced antibodies against the 27/28 kDa doublet. The results indicate that the 27 kDa serine protease of S. mansoni larvae is a target that is sensitive to immunological attack.

Type
Research Article
Copyright
1997 Cambridge University Press

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