The surface variant antigens of Plasmodium falciparum contain cross-reactive epitopes

Abstract

Plasmodium falciparum parasites evade the host immune system by clonal expression of the variant antigen, P. falciparum erythrocyte membrane protein 1 (PfEMP1). Antibodies to PfEMP1 correlate with development of clinical immunity but are predominantly variant-specific. To overcome this major limitation for vaccine development, we set out to identify cross-reactive epitopes on the surface of parasitized erythrocytes (PEs). We prepared mAbs to the cysteine-rich interdomain region 1 (CIDR1) of PfEMP1 that is functionally conserved for binding to CD36. Two mAbs, targeting different regions of CIDR1, reacted with multiple P. falciparum strains expressing variant PfEMP1s. One of these mAbs, mAb 6A2-B1, recognized nine of 10 strains tested, failing to react with only one strain that does not bind CD36. Flow cytometry with Chinese hamster ovary cells expressing variant CIDR1s demonstrated that both mAbs recognized the CIDR1 of various CD36-binding PfEMP1s and are truly cross-reactive. The demonstration of cross-reactive epitopes on the PE surface provides further credence for development of effective vaccines against the variant antigen on the surface of P. falciparum-infected erythrocytes.

Immunization of Aotus monkeys with a functional domain of the Plasmodium falciparum variant antigen induces protection against a lethal parasite line

“…This is suggested by the boost in the antibody response to the respective 179 region by exposure to PEs expressing homologous and heterologous CIDR1 and was not observed in monkeys without y179 immunization (19). It is possible that this critical region is cryptic because of immunodominant variant epitopes in other regions of PfEMP1 (19,23,33). We provide data that immunization with y179 overcomes its cryptic nature and can lead to ''determinant spreading'' with subsequent P. falciparum infections (34).…”

“…ELISA, agglutination, and flow cytometry assays were performed as described (23). ELISA was performed with glutathione S-transferase-179, y179, or yPyCSP at 1 g͞ml by using 1:5,000 dilution alkaline phosphatase-conjugated goat anti-human IgG (Kirkegaard & Perry Laboratories).…”

“…ELISA was performed with glutathione S-transferase-179, y179, or yPyCSP at 1 g͞ml by using 1:5,000 dilution alkaline phosphatase-conjugated goat anti-human IgG (Kirkegaard & Perry Laboratories). Agglutination scores (0-5) were determined according to size and number of agglutinates as described (23). Flow cytometry was performed as described (23) with monkey sera diluted 1:250 followed by fluorescein-labeled goat antihuman IgG (Kirkegaard & Perry Laboratories) at 1:100 dilution.…”

“…Agglutination scores (0-5) were determined according to size and number of agglutinates as described (23). Flow cytometry was performed as described (23) with monkey sera diluted 1:250 followed by fluorescein-labeled goat antihuman IgG (Kirkegaard & Perry Laboratories) at 1:100 dilution. Results are given as median fluorescence intensity.…”

The Low Sulfated Chondroitin Sulfate Proteoglycans of Human Placenta Have Sulfate Group-clustered Domains That Can Efficiently Bind Plasmodium falciparum-infected Erythrocytes

“…P. falciparum EMP1 can bind, in a domain-specific manner, CD36, intercellular adhesion molecule-1, vascular cell adhesion molecule-1, E-selectin, platelet endothelial cell adhesion molecule-1/CD31, and thrombospondin on vascular endothelial cell surface (18 -24). In addition, P. falciparum EMP1 can also bind complement receptor (25), heparan sulfate (20), and chondroitin 4-sulfate (C4S) (22)(23)(24)(25)(26)(27)(28). Thus, the parasite, by its ability to express divergent P. falciparum EMP1s using the var gene repertoire, can adhere to various organs.…”