Saposin-like proteins are expressed in the gastrodermis of Schistosoma mansoni and are immunogenic in natural infections.
BACKGROUND
Schistosomes are parasitic blood flukes that inhabit the portal blood system of humans. Ingested red cells are lysed in the gastrodermis to enable the parasites to digest hemoglobin. Saposin-like proteins (SAPLIPs) have been reported from the gastrodermis of related flukes, and at least one is hemolytic and a promising vaccine antigen. We now provide the first report of SAPLIPs from schistosomes and explore their role in host-parasite interactions.


METHODS
We identified expressed sequence tags encoding a family of SAPLIPs from Schistosoma mansoni and produced one (termed Sm-SLP-1) in recombinant form using baculovirus. The anatomic site of SLP-1 expression within the worm was assessed and its recognition by sera from chronically infected humans and mice was determined. The vaccine efficacy of Sm-SLP-1 was tested in a mouse model.


RESULTS
Full-length sequences were obtained for two cDNAs, Sm-slp-1 and Sm-slp-2. The Sm-slp-1 open reading frame contained a single SAPLIP domain while Sm-slp-2 had a double domain. Sm-SLP-1 was immunolocalized to the gastrodermis of adult worms, but did not confer protection in a murine vaccination model of schistosomiasis. Mice infected with S. mansoni generated a specific antibody response to Sm-SLP-1. Individuals who were infected with S. mansoni had IgG that recognized Sm-SLP-1. IgG levels were statistically higher in individuals with heavy infection.


CONCLUSIONS
Sm-SLP-1 is expressed in the gastrodermis of S. mansoni. It is immunogenic in humans and mice, but is not protective as a vaccine in its current form. Schistosome SAPLIPs warrant further attention to elucidate their roles in host-parasite interactions and to further explore their potential as vaccine and diagnostic antigens.
Don
Tegan A
TA
Division of Infectious Diseases and Immunology, Queensland Institute of Medical Research, 300 Herston Rd, Brisbane 4006, Queensland, Australia.
Bethony
Jeffrey M
JM
Loukas
Alex
A
D000595:Amino Acid Sequence; D000818:Animals; D000909:Antibodies, Helminth / Q000097:blood* / Q000276:immunology; D020405:Dermis / Q000378:metabolism*; D005260:Female; D005753:Gastric Mucosa / Q000378:metabolism*; D015723:Gene Library; D015801:Helminth Proteins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D006790:Host-Parasite Interactions; D006801:Humans; D051379:Mice; D008808:Mice, Inbred CBA; D008969:Molecular Sequence Data; D016133:Polymerase Chain Reaction; D011994:Recombinant Proteins / Q000235:genetics / Q000378:metabolism; D049231:Saposins / Q000235:genetics / Q000276:immunology / Q000378:metabolism; D012550:Schistosoma mansoni / Q000276:immunology* / Q000378:metabolism; D012555:Schistosomiasis mansoni / Q000276:immunology* / Q000469:parasitology / Q000517:prevention & control; D017422:Sequence Analysis, DNA; D014612:Vaccines
D000909:Antibodies, Helminth; D015801:Helminth Proteins; D011994:Recombinant Proteins; D049231:Saposins; D014612:Vaccines