Adherence of blood platelets and leucocytes to hybrid schistosomes

The bovine parasite, Schistosoma mattheei was crossed with the human schistosome, S. haematobium. The F1 hybrids resulting from this cross were viable in both snails and rodents. However, F1 x F1 (F2) crosses were less viable in snails and a proportion of them seemed to be changed structurally when viewed by scanning electron microscopy. Certain of the schistosomes were covered with a dense mass of interconnected blood platelets resembling a temporary haemostatic plug but not a blood clot. Interspersed between the platelets were a small number of leucocytes. We suggest that the platelets may have responded to the presence of an antigen which is masked in normal schistosomes but which is exposed in certain F2 hybrids.