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Evidence suggests that the helminth antioxidant enzyme superoxide dismutase (SOD) may play a role in parasite's defense against the cellular immune mechanisms of the host. In order to investigate this for the human parasite Onchocerca volvulus, the enzyme activity was characterized, the release of SOD by the parasite was examined, and a complete cDNA encoding the O. volvulus SOD was identified. The SOD activity in adult O. volvulus was found to be 8.1 +/- 4.2 U/mg of protein. A Cu/Zn-containing enzyme was demonstrated by its sensitivity towards cyanide, azide, and hydrogen peroxide. Isoelectric focusing, combined with an enzyme activity assay, revealed two activities at pI 6.8 and 7.6, with both activities inhibited by KCN. Adult parasites, maintained in vitro, released SOD into the culture medium, which was detected by enzyme activity. In parallel, lactate production was measured to ensure the viability of the parasite. Oligonucleotides (based upon conserved sequences in the SOD genes of other organisms) and the polymerase chain reaction were used to identify a portion of the SOD gene from O. volvulus genomic DNA. A cDNA library was constructed in lambda unizapII and screened with the genomic polymerase chain reaction fragment. A complete cDNA encoding the Cu/Zn SOD was identified, and its nucleotide sequence was determined. Southern blot hybridization experiments indicated that the Cu/Zn SOD is encoded by a single-copy gene with at least one intron.

Type A2 phospholipase (PLA2) activity has been observed in integral membrane protein extracts of Schistosoma japonicum. Antiserum raised against bee venom PLA2 recognized a single 16-kDa band in the parasite extracts; it also localized to antigen in the gut lining of fixed adult schistosomes as shown by immunofluorescence techniques. Evidence was obtained that the molecule was expressed at low levels in comparison with other integral membrane proteins and was weakly immunogenic in rabbits. Two oligonucleotide probes were constructed on the basis of highly conserved regions between the nucleotide sequences of rat, bovine, rattlesnake, and bee venom PLA2; these probes were used to isolate S. japonicum genomic DNA phage clones. A 1.8-kb FnuD2 fragment was shown by Southern blot analysis to strongly hybridize with the 5' 32P-labeled PLA2 oligonucleotides in both S. japonicum genomic DNA and DNA from one of the phage clones. The nucleotide and predicted amino acid sequences of this fragment revealed homology with the C terminus of PLA2s from different species.

The four closely related genes encoding eggshell proteins in the human parasite Schistosoma japonicum are described. A cDNA and a genomic DNA library were constructed and members of the eggshell protein gene family isolated. The four genes in this family do not contain introns, and differ in organization and nucleotide sequence from the related set of genes in Schistosoma mansoni and Schistosoma haematobium. The coding sequences of two of the S. japonicum genes and their flanking regions were determined. Transcription start sites for these genes were shown by primer extension analysis to occur 47 and 50 nucleotides in front of the start codon. A female-specific component in nuclear extracts binds to a DNA fragment containing conserved sequences upstream of the transcription start sites. The deduced protein sequences of 207 and 212 amino acids are composed of 50% glycine with continuous glycine regions as long as 11 residues. In vitro translations of male and female RNAs revealed female-specific translation products, the sizes of which were consistent with the eggshell proteins.

A Mr 23,000 Ag of the human trematode parasite, Schistosoma mansoni, has been identified by immunoscreening an adult worm cDNA library with antibody affinity purified on the Mr 23,000 to 25,000 integral membrane protein fraction of the parasite. This Ag is immunogenic in infected humans as well as in rabbits exposed to S. mansoni. The protein sequence of the Ag as deduced from cloned DNA sequences is 218 amino acids long and contains four putative transmembrane regions. Of particular significance, the Ag is strikingly similar, with respect to both amino acid sequence (36% identity) and putative domain structure to ME491, a human stage-specific melanoma-associated Ag.

Both Schistosoma japonicum and S. mansoni contain 28- and 26-kDa glutathione S-transferases (GSTs). Despite their immunological cross-reactivity using rabbit antisera, the S. japonicum 28-kDa GST (Sj28) is weakly immunogenic relative to the S. mansoni protein (Sm28) in mouse immunization experiments using GSTs purified from adult worms. The difference in immunogenicity is also observed during schistosome infection in mice. Using surface-labeled living S. japonicum worms, evidence was obtained for a surface location of Sj28 comparable to that reported for the S. mansoni molecule. The nucleotide and deduced amino acid sequences of cDNA clones corresponding to Sj28 and Sm28 were compared. Despite obvious homology (77% identity), differences were found in regions known to contain T epitopes in the S. mansoni protein which may be an explanation for the striking differences in immunogenicity in regard to antibody production in mice. The 26-kDa GSTs of these two parasites (Sj26 and Sm26) are also closely related on the basis of nucleotide and deduced amino acid sequences, there being 82% identity in the putative coding regions. When the amino acid sequences of Sj28 and Sm28 were compared with those of Sj26 and Sm26, the overall sequence identity was approximately 20%. However, a relatively conserved region was identified in otherwise structurally different molecules which may participate in common properties of these enzymes.

A 43-kDa putative lipoprotein receptor (Sj43) of adult Schistosoma japonicum worms has been identified using ligand blotting techniques. Single and two dimensional electrophoretic analyses showed that Sj43 consisted of a single acidic polypeptide with multiple lipoprotein specificity. The molecule bound 125I-labelled low-density (apo-B), very low-density or high-density (apo-A and/or apo-C) lipoproteins from different mammalian hosts that are permissive to S. japonicum infection, but did not bind mouse apo-A containing lipoprotein. The binding of 125I-labelled lipoprotein to Sj43 could be inhibited by unlabelled human LDL, EDTA or Suramin, or by chemical modification of lipoprotein lysine or arginine residues. Sj43 was localised at the parasite's tegument and gut lining.