Apicomplexan parasites include those of the generaPlasmodium,Cryptosporidium, andToxoplasmaand those of the relatively understudied zoonotic genusBabesia. In humans, babesiosis, particularly transfusion-transmitted babesiosis, has been emerging as a major threat to public health. Like malaria, the disease pathology is a consequence of the parasitemia which develops through cyclical replication ofBabesiaparasites in host erythrocytes. However, there are no exoerythrocytic stages inBabesia, so targeting of the blood stage and associated proteins to directly prevent parasite invasion is the most desirable option for effective disease control. Especially promising among such molecules are the rhoptry neck proteins (RONs), whose homologs have been identified in many apicomplexan parasites. RONs are involved in the formation of the moving junction, along with AMA1, but no RON has been identified and characterized in anyBabesiaspp. Here we identify the RON2 proteins ofBabesia divergens(BdRON2) andB. microti(BmRON2) and show that they are localized apically and that anti-BdRON2 antibodies are significant inhibitors of parasite invasionin vitro. Neither protein is immunodominant, as both proteins react only marginally with sera from infected animals. Further characterization of the direct role of both BdRON2 and BmRON2 in parasite invasion is required, but knowledge of the level of conformity of RON2 proteins within the apicomplexan phylum, particularly that of the AMA1-RON2 complex at the moving junction, along with the availability of an animal model forB. microtistudies, provides a key to target this complex with a goal of preventing the erythrocytic invasion of these parasites and to further our understanding of the role of these conserved ligands in invasion.
Identification and characterization of peptidoglycan-associated proteins in Neisseria gonorrhoeae.
