EQUILIBRIUM IN LUNG SCHISTOSOMULA SPHINGOMYELIN BREAKDOWN AND BIOSYNTHESIS ALLOWS VERY SMALL MOLECULES, BUT NOT ANTIBODY, TO ACCESS PROTEINS AT THE HOST–PARASITE INTERFACE

The mechanism by which lung-stage schistosomula expose proteins at the host–parasite interface to nutrient, but not antibody, uptake has been obscure. We have found that Schistosoma mansoni and Schistosoma haematobium larvae emerging from host lung at a pH of around 7.5, and fixed with diluted formaldehyde (HCHO), readily bind specific antibodies in indirect membrane immunofluorescence. Data on inhibitors and activators of parasite tegument-bound, magnesium-dependent, neutral sphingomyelinase (nSMase), and sphingomyelin biosynthesis inhibitors revealed that equilibrium in schistosomular sphingomyelin breakdown and biosynthesis prevents antibody binding, yet permits access of small HO-CH₂-OH polymers to interact with and cross-link proteins at the host–parasite interface, allowing for their serological visualization.