SPECIFIC BINDING OF HUMAN LOW-DENSITY-LIPOPROTEIN TO THE SURFACE OF SCHISTOSOMULA OF SCHISTOSOMA-MANSONI AND INGESTION BY THE PARASITE

Low-density lipoproteins (LDL)1 may be important in human schistosomiasis because LDL bound to the surface of the parasite inhibits the binding of antischistosomal antibodies. Low-density lipoproteins also may serve as a source of lipids for the parasite membrane synthesis. Here LDL fluorescently labeled with carbocyanine dye (Dil-LDL) was used to measure the specificity of binding of LDL to the surface of schistosomula of Schistosoma mansoni and to examine the distribution of the LDL particles over time. Dil-LDL binding was saturable and specific, with strong inhibition by unlabeled LDL and apoB but not by apoA1, bovine serum albumin, or IgG, and only weak inhibition by high-density lipoproteins. Half of the bound Dil-LDL was displaced by unlabeled LDL. Dil-LDL remained bound on the surface of schistosomula for up to 36 hours in culture. However parasites also ingested both Dil-LDL and a second fluorescent LDL, Bodipy-LDL. Over time, both fluorophores appeared throughout the worm tissues, suggesting the LDL particles were breaking down and that the fluorophores and lipids originally contained within the LDL particle were partitioning throughout the worm. Thus human LDL appears to bind to the surface of schistosomula specifically. Ingested LDL appears to be broken down and may serve as a source of host lipids for the parasite.