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Abstract
BackgroundPlasmodium falciparum STEVOR proteins, encoded by the multicopy stevor gene family have no known biological functions. Their expression and unique locations in different parasite life cycle stages evoke multiple functionalities. Their abundance and hypervariability support a role in antigenic variation.MethodsImmunoblotting of total parasite proteins with an anti-STEVOR antibody was used to identify variant antigens of this gene family and to follow changes in STEVOR expression in parasite populations panned on CSA or CD36 receptors. Immunofluorescence assays and immunoelectron microscopy were performed to study the subcellular localization of STEVOR proteins in different parasite stages. The capacity of the antibody to inhibit merozoite invasion of erythrocytes was assessed to determine whether STEVOR variants were involved in the invasion process.ResultsAntigenic variation of STEVORs at the protein level was observed in blood stage parasites. STEVOR variants were found to be present on the merozoite surface and in rhoptries. An insight into a participation in erythrocyte invasion was gained through an immunofluorescence analysis of a sequence of thin slides representing progressive steps in erythrocyte invasion. An interesting feature of the staining pattern was what appeared to be the release of STEVORs around the invading merozoites. Because the anti-STEVOR antibody did not inhibit invasion, the role of STEVORs in this process remains unknown.ConclusionThe localization of STEVOR proteins to the merozoite surface and the rhoptries together with its prevalence as a released component in the invading merozoite suggest a role of these antigens in adhesion and/or immune evasion in the erythrocyte invasion process. These observations would also justify STEVORs for undergoing antigenic variation. Even though a role in erythrocyte invasion remains speculative, an association of members of the STEVOR protein family with invasion-related events has been shown.
Highlights
Plasmodium falciparum STEVOR proteins, encoded by the multicopy stevor gene family have no known biological functions
The multicopy var gene family encoding variant surface antigens known as P. falciparum erythrocyte membrane protein 1 (PfEMP1) is the best characterized exported protein that undergoes antigenic variation
Transcription studies demonstrated that the expression of stevor and Pfmc-2TM gene families is clonally variant and undergoes switching [7], but confirmation of antigenic variation at the protein level is lacking
Summary
Plasmodium falciparum STEVOR proteins, encoded by the multicopy stevor gene family have no known biological functions. Their expression and unique locations in different parasite life cycle stages evoke multiple functionalities. Their abundance and hypervariability support a role in antigenic variation. The multicopy var gene family encoding variant surface antigens known as P. falciparum erythrocyte membrane protein 1 (PfEMP1) is the best characterized exported protein that undergoes antigenic variation (reviewed in [2]). Transcription studies demonstrated that the expression of stevor and Pfmc-2TM gene families is clonally variant and undergoes switching [7], but confirmation of antigenic variation at the protein level is lacking
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