Immunological and protection studies.

(A) Indirect immunofluorescence assay using group A Aotus monkey's sera (obtained 20 days after the 3rd immunization with HABP 24112 and 1 day prior to challenge), displaying a merozoite membrane reactivity pattern characteristic of MSP-2's localization in late schizonts. (B) Western blot analysis of schizont-lysate P. falciparum proteins reacting with sera from Group A monkeys (monkeys 192, 149, 250, 259, 239 and 277), obtained 20 days after the 3rd immunization and the day previous to the challenge, tested at 1∶200 dilution. Sera are recognizing P. falciparum proteins of 69 kDa and cleavage fragments of 63, 54, 51 and 48 kDa. (C) Parasitemias developed in immunized Aotus monkeys from groups A–C and the control group D. The percentage of parasitized red blood cells was evaluated daily by Acridine Orange staining read on a fluorescence microscope, starting on day 4 post-challenge and until day 15. In those fully protected Aotus monkeys the complete slide was read with ∼1.000.000 RBCs being screened. Each monkey in each group is represented by a different symbol.