Immunoelectron microscopy of Schuffner's dots in Plasmodium vivax-infected human erythrocytes

Abstract

Plasmodium vivax induces morphologic alterations in infected host erythrocytes that are visible by light microscopy in Romanovsky-stained blood smears as multiple brick-red dots. These morphologic changes, referred to as Schuffner's dots, are important in the identification of this species of malarial parasite and have been associated by electron microscopy with caveola-vesicle complexes along the erythrocyte plasmalemma. We have produced a monoclonal antibody (MAb A 20) that identifies an antigen in Plasmodium vivax-infected erythrocytes that is associated with the caveola-vesicle complexes of the parasitized host cell. This monoclonal antibody reacts with air-dried P. vivax-infected erythrocytes to produce a pattern by the indirect immunofluorescence test (IFT) that is evocative of Schuffner's dots. Immunoelectron microscopy of P. vivax-infected human erythrocytes using MAb A 20 confirmed the location of this antigen within vesicles of caveola-vesicle complexes. On Western blots MAb A 20 recognized four polypeptides of 54, 64, 72, and 86 kd. MAb A 20 reacted by IFT with 90% of Sri Lankan isolates and with a Brazilian P. vixax isolate, which indicates that the epitope identified by this monoclonal is conserved.