Plasmodium falciparum surface-related antigen (PfSRA) localized on the merozoite surface is carried along with the glycosylphosphatidylinositol-anchored MSP119 into invaded erythrocytes. A, Colabeling of rabbit α-PfSRA-1 (1:100; red) with mouse α-PfMSP119 (1:100; green) antibodies in released merozoites shows that PfSRA is localized on the merozoite surface. Colocalization coefficient (R) is displayed at the far right. Secondary antibodies used are Alexa 488–conjugated goat α-mouse immunoglobulin G (IgG) and Alexa 568–conjugated goat α-rabbit IgG .Nuclei were stained with 4′,6-diamidino-2-phenylindole (DAPI) (blue). B, Nonpermeabilized, liquid immunofluorescence assays (IFAs) show colabeling of rabbit α-PfSRA-1 (1:100; green) with mouse α-PfAMA-1 (1:100; red) antibodies on the surface of released merozoites. Secondary antibodies used are Alexa 568–conjugated goat α-rat IgG and Alexa 488–conjugated goat α-rabbit IgG (1:200; Life Technologies). Permeabilized IFAs show colabeling of rabbit α-PfSRA-1 (1:100; red) and mouse α-Pfs48/45 (green). Secondary antibodies used were Alexa 568–conjugated goat α-rabbit IgG and Alexa 488–conjugated goat α-mouse IgG, (1:200; Life Technologies). Exposure times are identical for all images of the same channel. Nuclei were stained with DAPI (blue). C, Colabeling of schizont, released merozoite, and internalized merozoites with rabbit α-PfSRA P3 (red) and mouse α-Pfs48/45 (green) show staining of the different parasite stages, but no staining was observed for the gametocyte surface marker, Pfs48/45. Nuclei were stained with DAPI (blue). Secondary antibodies used were Alexa 488–conjugated goat α-mouse IgG and Alexa 568–conjugated goat α-rabbit IgG (1:200; Life Technologies). D, Invading merozoites were colabeled with α-MSP119 (red) and α-PfSRA P3 (green) to show the internalization of both proteins during invasion, and antibody labeling with both was visible at the development of ring-stage parasites. Secondary antibodies used were Alexa 488–conjugated goat α-mouse IgG and Alexa 568–conjugated goat α-rabbit IgG (1:200; Life Technologies). Abbreviations: BP, brightfield; DAPI, 4′,6-diamidino-2-phenylindole; PfSRA, Plasmodium falciparum surface-related antigen.

Amlabu E, Mensah-Brown H, Nyarko PB, Akuh OA, Opoku G, Ilani P, Oyagbenro R, Asiedu K, Aniweh Y, Awandare GA. Functional Characterization of Plasmodium falciparum Surface Related Antigen (PfSRA) as a Potential Blood-Stage Vaccine Target. J Infect Dis. 2018 Apr 18. [Epub ahead of print]