Babesia bigemina: identification of B cell epitopes associated with parasitized erythrocytes.
Rhoptries are involved in host cell invasion and rhoptry polypeptides, including the Babesia bigemina rhoptry-associated protein-1 (RAP-1), are targets for protective immune responses. Polyclonal antisera produced against isolated rhoptries is directed predominantly against RAP-1 and reacts with both the merozoite and the membrane of parasitized erythrocytes. To determine whether these B cell epitopes associated with the parasitized erythrocyte are derived from RAP-1 or, alternatively, from previously undetected merozoite polypeptides, monoclonal antibodies (mAbs) were generated from mice immunized with rhoptries isolated from the JG-29 clone of the Mexico strain. The anti-RAP-1 mAbs bound only merozoites in a punctate immunofluorescence pattern. A second group of four mAbs, none of which were reactive with RAP-1, bound the parasitized erythrocyte. Two of these latter mAbs, 64/44.17.3 and 64/05.7.2, reacted only with parasitized erythrocytes that had been permeabilized. MAb 64/44.17.3 bound a 54-kDa merozoite polypeptide while 64/05.7.2 bound a > or = 225-kDa merozoite polypeptide. MAbs 64/32.8.5 and 64/38.5.3 recognized epitopes on 17.5- and 76-kDa polypeptides exposed on the external surface of intact parasitized erythrocytes. The results indicate that the identified RAP-1 epitopes are not associated with the erythrocyte cytoskeleton or membrane and that anti-RAP-1 immunity is most likely generated against the free merozoite. All new mAbs reacted with every B. bigemina strain tested (Mexico, Puerto Rico, St. Croix, Texcoco, Jaboticabal). The conservation of RAP-1 epitopes among these strains supports the continued testing of RAP-1 as a vaccine component. In addition, the identification of epitopes expressed on the surface of erythrocytes infected with all five strains provides new candidate immunogens.
Vidotto
O
O
Department of Veterinary Microbiology and Pathology, Washington State University, Pullman 99164-7040, USA.
McElwain
T F
TF
Machado
R Z
RZ
Perryman
L E
LE
Suarez
C E
CE
Palmer
G H
GH
D000818:Animals; D000911:Antibodies, Monoclonal; D000953:Antigens, Protozoan / Q000276:immunology*; D001402:B-Lymphocytes / Q000276:immunology*; D001403:Babesia / Q000276:immunology*; D016793:Babesia bovis / Q000276:immunology; D015153:Blotting, Western; D002417:Cattle; D000939:Epitopes; D004912:Erythrocytes / Q000469:parasitology*; D005455:Fluorescent Antibody Technique; D011233:Precipitin Tests; D015800:Protozoan Proteins / Q000276:immunology*
D000911:Antibodies, Monoclonal; D000953:Antigens, Protozoan; D000939:Epitopes; D015800:Protozoan Proteins; C097551:rhoptry-associated protein-1, Babesia