Immunity of Babesia divergens in the rat. Histology of the infected liver and its possible role in removing PRBC's.

The ability of immune rats to resist challenge with Babesia divergens depends upon mechanisms which are largely spleen independent. The possible removal of B. divergens PREC's by the livers of immune splenectomised rats was investigated. The clearance of Cr51 labeled B. divergens infected erythrocytes was followed in splenectomised rats to test whether Cr51 labeled PREC's are cleared from the circulation of immune rats through uptake and phagocytosis by the liver. No significant difference was observed between the clearance radioactivity from the circulation as well as the liver uptake in the immune rats from the controls. The uptake of infected erythrocytes by the liver is unlikely to happen in immune rats. Other unknown mechanisms appear to take part in clearing the parasitaemia in these rats. This might depend upon antibody inhibition of merozoite invasion. The injection of irradiated parasites into the same rats showed that they were able to clear PRBC's from the blood stream and that immunity was not specifically directed at merozoites. It is speculated that parasites inside red cells are removed by lysis or phagocytosis. Histological studies on livers collected from immune rats showed that lymphocytes are accumulated in the Liver and these consisted of B & T cells leukocytes accumulating in the liver might therefore be very important in the development of acquired immunity to B. divergens in splenectomised rats.