Serum-induced expression of a surface protein in schistosomula of Schistosoma mansoni: a possible receptor for lipid uptake.

When freshly transformed schistosomula of Schistosoma mansoni are incubated with human serum, a protein doublet (molecular weight approximately 45 kDa) is expressed on the surfaces of the parasites; parasites incubated in defined media fail to express the doublet proteins. A 30 min exposure to serum is sufficient to induce the expression of the doublet, and even when the parasites are separated from the serum by a dialysis membrane, the doublet is still expressed. The doublet proteins are shown to be synthesized by cercariae, but not by schistosomula; they can be extracted using detergents and immunoprecipitated by specific antisera. Following expression of the doublet, purified low density lipoproteins from human serum interact with the schistosomula, become adsorbed onto their surface membranes and are possibly internalized and degraded.