Plasmodium berghei development in irradiated sporozoite-immunized C57BL6 mice

The C57BL6 strain of mice is highly susceptible to Plasmodium berghei sporo zoite infections and consequently requires repeated immunizations with irra diated sporozoites to obtain protective immunity. After a live sporozoite c hallenge in the immunized hosts, hepatic-stage parasites found in the liver after 48 h are of different sizes - small schizonts corresponding to block ed forms (derived from irradiated sporozoites), and schizonts of intermedia te size (derived from live sporozoites). Large schizonts corresponding to m ature hepatic forms are found only in unimmunized but challenged C57BL6 mic e. Using monoclonal and polyclonal antibodies directed to liver-stage paras ites, different patterns of binding reactivity to the above forms are obser ved. More than 20 % of the irradiated sporozoites transform into blocked fo rms after immunization and persist in the liver. Upon sporozoite challenge in such immunized animals the rate of transformation of sporozoites into he patic parasites is less than 2 %. These observations shed light on the fate of live sporozoite development in irradiated sporozoite-immunized C57BL6 m ice.