Overall, RAS or CPS immunizations resulted in sporozoite-specific IFNγ responses in the liver (P = 0.03) and spleen (P = 0.008). Although not reaching statistical significance, there was a tendency of higher sporozoite-specific IFNγ response by

T cells with memory phenotype (CD44hi) in liver and spleen (Figure 2b) cells from IV immunized compared to ID immunized C57BL/6J mice. Within the T-cell population, similar observations were made for CD8+CD44hi T cells. Furthermore, the levels of CD8+ Tem cells in both IV and ID groups correlated with the IFNγ response in liver (R = 0.63, P = 0.003) and spleen (R = 0.54, P = 0.01). Three weeks after challenge, the observed high levels of liver CD8+ Tem cells (Figure 2c) and increased IFNγ responses (Figure 2d) were sustained in Selleckchem AP24534 IV immunized mice. No data were obtained from ID immunized mice as these did not

survive challenge infection (Table 1). Finally, functionality of RAS- and CPS-induced antibodies was tested in the sporozoite neutralization assay, testing their capacity to invade and subsequently develop in liver cells (24). Sporozoite invasion was strongly reduced in the presence of plasma from both RAS and CPS immunized mice (P ≤ 0.05), with stronger inhibition by IV immunized mice within the RAS group (P < 0.01) (Figure 3). As CPS ID immunized mice showed similar blocking activity compared to IV immunized mice, antibodies may contribute but are by themselves likely not selleck inhibitor sufficient

to induce complete protection. Our findings show that ID immunization Tryptophan synthase with whole live malaria parasites confers a far lower protective efficacy when compared to IV immunization. The reduced protective efficacy clearly associates with a lower number of sporozoites reaching the liver. Lower protective efficacy by ID immunization was observed in both BALB/c and C57BL6/j mice using two independent immunization protocols, that is, sporozoite liver cell invasion only with early developmental arrest (RAS) or full completion of liver maturation and early abrogation of blood-stage multiplication (CPS). Moreover, both RAS and CPS IV immunizations induce higher cellular immune responses compared to ID. Our data confirm the earlier formulated hypothesis by Epstein et al. (18): based on low hepatic immune responses in ID immunized animals and low protection level in a clinical trial, the authors suggest that the degree of parasite liver load following sporozoite administration associates with protective efficacy. However, ID immunization can induce high levels of protection provided that sufficiently high numbers of sporozoites (i.e. 9 × 104P. yoelii) are injected (17). The necessity of high numbers of sporozoites for ID induced protection supports the notion that liver parasite load might be important for protective efficacy of whole sporozoite immunization. ID injection of P.