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Abstract. The technique of fluorescence recovery after photobleaching was used to measure the lateral diffusion of fluorescent lipid analogues in the surface membrane of Schistosoma mansoni. Our data reveal that although some lipids could diffuse freely others exhibited restricted lateral diffusion. Quenching of lipid fluorescence by a non-permeant quencher, trypan blue, showed that there was an asymmetric distribution of lipids across the double bilayer of mature parasites. Those lipids that diffused freely were found to reside mainly in the external monolayer of the outer membrane whereas lipids with restricted lateral diffusion were located mainly in one or more of the monolayers beneath the external monolayer. Formation of surface membrane blebs allowed us to measure the lateral diffusion of lipids in the membrane without the influence of underlying cytoskeletal structures. The restricted diffusion found on the normal surface membrane of mature parasites was found to be released in membrane blebs. Quenching of fluorescent lipids on blebs indicated that all probes were present almost entirely in the external monolayer. Juvenile worms exhibited lower lateral diffusion coefficients than mature parasites: in addition, the lipids partitioned into the external monolayer. The results are discussed in terms of membrane organization, cytoskeletal contacts, and biological significance.

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Three monoclonal antibodies (K2-4F2, K3-2F2, and K3-4C8) of the immunoglobulin G2a class were raised against hepatitis A virus. The specificity of these antibodies was confirmed by immune electron microscopy, solid-phase radioimmunoassay, and in vitro neutralization in cell culture. Binding studies suggested that they all recognize closely related antigenic determinants. These monoclonal antibodies should prove to be of great value as diagnostic and research reagents.

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