Detection of antibodies to platelets and erythrocytes during infection with haemorrhage-causing Trypanosoma vivax in Ayrshire cattle.

Ayrshire cattle, which were infected with a stock of Trypanosoma vivax from Galana, Kenya, which produced haemorrhagic disease, were examined for the presence of antibodies to erythrocytes and platelets. Antibodies to normal erythrocytes and platelets were detected in the plasma of infected animals using the enzyme-linked immunosorbent assay (ELISA). The antibodies were detectable following the first peak of parasitaemia (10-15 days after infection) and antibody activity was maximal 30-35 days after infection. Plasma from cattle, taken 32 days after infection, precipitated radiolabelled proteins from autologous platelets and, less efficiently, from autologous erythrocytes. Fluorescence-activated cell sorter (FACS) assays demonstrated that erythrocytes and platelets from infected cattle bound IgM and IgG in vivo, and that both normal blood cell types could adsorb these antibodies following incubation in plasma from infected animals. Complement (C3) was similarly adsorbed to erythrocytes during infection. Antibodies adsorbed to infected erythrocytes could be eluted and the eluted antibodies bound to normal erythrocytes, as detected by immunofluorescence, but they did not react with the infecting trypanosome. It is hypothesised that although anti-blood cell antibodies may not be the primary cause of the severe anaemia and thrombocytopaenia which accompany the haemorrhagic syndrome, they could play an important role in the maintenance of these signs of disease, adversely affecting the outcome of T. vivax-associated haemorrhagic disease in the field.