SLTRiP immunization, antibody specificity, and sporozoite challenge assay.
A, antibody titers of mouse anti-SLTRiP polyclonal sera determined by the ELISA method. Error bar represents the standard deviation. Cont, control. B, mouse polyclonal sera generated against purified SLTRiP specifically recognizes SLTRiP in sporozoite lysate. Lane 1, purified recombinant GST-SLTRIP (72.5 kDa, E. coli expressed); lane 2, SLTRiP-KO sporozoite lysate; lane 3, WT blood stage lysate; lane 4, WT sporozoite lysate; and lane 5, protein molecular mass markers. Western blotting with anti-CSP antibody serves as control for KO and WT sporozoite samples. β-Actin was used as loading control. C, SLTRiP immunized mice show a 4-day delay in the first emergence of blood stage infection as compared with control group. Each data point represents the average parasitemia from five mice. D, parasite load in the livers of SLTRiP immunized mice as measured by qPCR for parasite 18S-rRNA copy numbers. The parasite load in the livers of SLTRiP immunized mice is 4 log scale (10,000 times) lower as compared with the control group of mice. Each bar represents the average 18S-rRNA copy number from five mice. Error bars represent the standard deviation in each group. *, p < 0.005. E, SNA with SLTRiP-Ab compared with the control sera. Infection was determined by measuring parasite 18S-rRNA copy numbers in samples using real time PCR. Error bars represent the standard deviation in each group. ns, not significant. p > 0.1.