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.

Tetraspanins on the surface of Schistosoma mansoni are protective antigens against schistosomiasis.

Schistosomes are blood-dwelling flukes that infect 200 million people worldwide and are responsible for hundreds of thousands of deaths annually. Using a signal sequence trap, we cloned from Schistosoma mansoni two cDNAs, Sm-tsp-1 and Sm-tsp-2, encoding the tetraspanin (TSP) integral membrane proteins TSP-1 and TSP-2. We raised antibodies to recombinant TSP fusion proteins and showed that both proteins are exposed on the surface of S. mansoni. Recombinant TSP-2, but not TSP-1, is strongly recognized by IgG1 and IgG3 (but not IgE) from naturally resistant individuals but is not recognized by IgG from chronically infected or unexposed individuals. Vaccination of mice with the recombinant proteins followed by challenge infection with S. mansoni resulted in reductions of 57% and 64% (TSP-2) and 34% and 52% (TSP-1) for mean adult worm burdens and liver egg burdens, respectively, over two independent trials. Fecal egg counts were reduced by 65-69% in both test groups. TSP-2 in particular provided protection in excess of the 40% benchmark set by the World Health Organization for progression of schistosome vaccine antigens into clinical trials. When coupled with its selective recognition by naturally resistant people, TSP-2 seems to be an effective vaccine antigen against S. mansoni.

A pore-forming haemolysin from the hookworm, Ancylostoma caninum.

Hookworms feed on blood, but the mechanism by which they lyse ingested erythrocytes is unknown. Here we show that Ancylostoma caninum, the common dog hookworm, expresses a detergent soluble, haemolytic factor. Activity was identified in both adult and larval stages, was heat-stable and unaffected by the addition of protease inhibitors, metal ions, chelators and reducing agents. Trypsin ablated lysis indicating that the haemolysin is a protein. A closely migrating doublet of hookworm proteins with apparent molecular weights of 60-65 kDa bound to the erythrocyte membrane after lysis of cells using both unlabeled and biotinylated detergent-solubilised hookworm extracts. In addition, separation of detergent-soluble parasite extracts using strong cation-exchange chromatography, resulted in purification of 60-65 kDa proteins with trypsin-sensitive haemolytic activity. Erythrocytes lysed with particulate, buffer-insoluble worm extracts were observed using scanning electron microscopy and appeared as red cell ghosts with approximately 100 nm diameter pores formed in the cell membranes. Red blood cell ghosts remained visible indicating that lysis was likely caused by pore formation and followed by osmotic disruption of the cell.