One of the most comprehensive studies of this phenomenon to date was conducted using the rodent malaria parasite Plasmodium chabaudi chabaudi, for which it was shown that the major genetic determinant of the strain-specificity of the immunity achieved via immunization with blood-stage parasites is the merozoite surface protein

1 gene (msp1) (3). Natural malaria infections of both rodents and humans are initiated by the bite of malaria parasite-infected Anopheles see more mosquitoes, which inoculate sporozoites into the skin during blood feeding. Very effective protective immunity against malaria can be achieved by immunization with sporozoites that have been attenuated by irradiation (4). More recently, other methods of sporozoite attenuation such as genetic modification (5) and chemical attenuation (6) have also been shown to confer protective immunity against re-infection. A similar approach in which live sporozoites are inoculated contemporaneously with anti-erythrocytic stage drugs such as chloroquine (CQ) has recently been shown to confer sterile protective immunity against Plasmodium falciparum in human volunteers CHIR-99021 cell line (7).

The protective efficacies of these vaccine strategies have, most commonly, been assessed using parasites homologous to the vaccinating strain. Those few studies which have assessed the level of protection against heterologous challenge have almost exclusively assessed the degree of cross-protection between malaria parasite species (8–15) and are generally inconsistent

see more in their conclusions. Should it occur, parasite strain-specificity to the induction of immunity by live sporozoites of P. falciparum will need to be understood if such vaccination is to be used effectively. Here, we present the results of experiments to test for and determine the degree of cross protection between strains of Plasmodium chabaudi immunized by inoculation of live sporozoites in conjunction with mefloquine (MF) treatment. All experiments were carried out in compliance with the British Home Office Animals (Scientific Procedures) Act 1986. For sporozoite immunizations, two groups of 20 inbred female CBA/Ca mice (6 weeks old at the time of first immunization) were inoculated via intraperitoneal (IP) injection with known numbers of sporozoites of P. c. chabaudi clones AJ or CB diluted in a 50 : 50 mixture of Foetal Calf Serum (FCS) and Ringer’s solution contemporaneously with oral MF treatment (20 mg/kg/day for 5 days). Immunizations were performed twice with an interval of 3 weeks between inoculations. Each mouse received an inoculation of ∼400 sporozoites of each strain in the first immunization, and ∼2000 in the second. Twenty control mice were inoculated with 50 : 50 FCS: Ringer’s solution only, and also drug treated. Five weeks following the second immunization, mice were each challenged IP with 2400 sporozoites of either strain, or with 1 × 106 parasite-infected red blood cells (iRBCs).