Plasmodium berghei: Production and Quantitation of Hepatic Stages Derived from Irradiated Sporozoites in Rats and Mice

Abstract

Immunization with irradiated-attenuated malaria sporozoites has been shown to protect both rodents and humans against a homologous sporozoite challenge. Irradiated-attenuated sporozoites retain their capacity to invade hepatocytes and transform into trophozoites without undergoing complete schizogony. As a result, the minute size of these trophozoites (4-8 microns) makes their detection by conventional microscopy difficult. An additional problem lies in obtaining sufficient quantities of exoerythrocytic stages of attenuated parasites in vivo to study their antigenic repertoire and the sequence of events that occur after immunization of hosts. We have used a previously described method of inoculating Plasmodium berghei sporozoites directly into specific liver lobes (HPBI = hepatic portal branch inoculation) to improve parasite yields. Comparing HPBI with tail vein inoculation of sporozoites in Brown Norway rats and C57BL/6 mice revealed up to a 6-fold increase in hepatic parasite yields by HPBI method. The inoculation of 3 x 10(6) irradiated sporozoites via HPBI yielded 139 +/- 2 and 69 +/- 2 exoerythrocytic parasites per cm2 of liver in Brown Norway rats and C57BL/6 mice, respectively. The HPBI method therefore not only facilitates visualization of a large number of irradiated hepatic stage parasites within the defined lobes of the liver but also provides ample numbers of parasites for immunization and for immunological analysis.

Reduced Plasmodium berghei sporozoite liver load associates with low protective efficacy after intradermal immunization

“…Whole parasite immunizations with sporozoites attenuated by radiation (RAS), or with sporozoites in combination with chloroquine chemo-prophylaxis (CPS), have been successfully conducted in mice and men resulting in complete protection (4)(5)(6). RAS arrest early in liver stage development (7) whereas CPS undergo full liver stage maturation releasing blood-stage parasites that are subsequently killed by chloroquine (4). While murine immunizations are generally performed by intravenous (IV) routing, alternative routes are required for sustainable clinical applications in humans.…”

Maintenance of protective immunity against malaria by persistent hepatic parasites derived from irradiated sporozoites.

“…Parallel rpm, and then freeze-thawed six times. Rats were then immunized with an aliquot of liver homogenate containing approximately 200,000 disrupted parasites as described (19). No adjuvant was used.…”

New Potential Antimalarial Agents: Therapeutic-Index Evaluation of Pyrroloquinazolinediamine and Its Prodrugs in a Rat Model of Severe Malaria

“…A rat model of malaria which resembles malaria in humans in terms of its symptoms, hyperparasitemia, and lethality (5,9,30) has successfully been developed in our laboratory for efficacy and toxicity studies (24,31).…”