Immunological studies of the mechanism of anaemia in experimental Trypanosama evansi infection in rats

Pathological changes in the blood of rats acutely infected with Trypanosoma evansi and the probable mechanism of the accompanying anaemia, were investigated. A severe anaemia, together with rreticulocytosis and hepato-splenomegaly, were regularly observed. Histological examination of the liver, spleen and bone-marrow confirmed the increasedin erythropoietic activity that the observed anaemia was due to increasedextravascular destruction of erythrocytes rather than by inhibition of haemopoietic activity. All the infected rats showed significant immune responses to the infecting trypanosome peak agglutinin titres occurring 10–12 days after injection, coincidentally with maximun destruction of erythrocytes. Serological examination of sera and erythrocytes from all infected and control rats did not reveal the presence of either circulating or adsorbed erythrocyte auto--antibodies. Furthermore, there was no in vivo trypanosomal antigen coating of the erythrocytes from either infected or multiple antigen-injected rats. Repeated intraveoous injections into rats of more than 100 μg per g body weight of soluble T. evansi antigen resulted in moderately severe, probably antibody-mediated, haemolytic anaemia. It is considered that an immunologically-mediated mechanism may be responsible for the development of the anaemia accompanying T. evansi infection.