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. 2006 Mar 1;193(5):721-30.
doi: 10.1086/500145. Epub 2006 Jan 30.

Antigenic differences and conservation among placental Plasmodium falciparum-infected erythrocytes and acquisition of variant-specific and cross-reactive antibodies

James G Beeson  1 , Emily J Mann, Timothy J Byrne, Aphrodite Caragounis, Salenna R Elliott, Graham V Brown, Stephen J Rogerson
Affiliations

Antigenic differences and conservation among placental Plasmodium falciparum-infected erythrocytes and acquisition of variant-specific and cross-reactive antibodies

James G Beeson et al. J Infect Dis. .

Abstract

Background. Pregnant women are infected by Plasmodium falciparum with novel antigenic phenotypes that adhere to chondroitin sulfate A (CSA) and other receptors in the placenta. The diverse and variant parasite protein P. falciparum erythrocyte membrane protein 1 (PfEMP1), which is encoded by var genes, is a ligand for CSA and a major target of antibodies associated with protective immunity.Methods. Serum samples from pregnant women exposed to malaria were tested for immunoglobulin G, adhesion-inhibitory antibodies, and agglutinating antibodies to different CSA-binding isolates expressing conserved var2csa-type genes and to parasite isolates from infected placentas. Parasite isolates also were examined to assess PfEMP1 expression, the effect of trypsin treatment of infected erythrocytes on parasite adhesion and cleavage of PfEMP1, and inhibition of adhesion by rabbit antiserum raised against a CSA-binding isolate.Results. Findings demonstrated that (1) there are significant antigenic differences between CSA-binding isolates that correspond with polymorphisms in var2csa; (2) there are differences in the properties of PfEMP1 and antibody reactivity between CSA-binding and placental isolates, which express multiple PfEMP1 forms; (3) acquired antibodies target diverse and cross-reactive epitopes expressed by CSA-binding infected erythrocytes, and cross-reactive antibodies are not necessarily cross-inhibitory; and (4) the breadth of antibody reactivity is greater among multigravidae than among primigravidae.Conclusions. Immunity may be mediated by a repertoire of antibodies to diverse and common epitopes. Strategies based on vaccination with a single domain or isolate might be hindered by antigenic diversity.

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Figures

Figure 1
Figure 1
Demonstration, on Western blots, that 3 isolates selected for adhesion to chondroitin sulfate A (CSA) express Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) of the same relative molecular mass, whereas placental isolates appear to express multiple PfEMP1 forms. Membrane-bound proteins were extracted from P. falciparum-infected erythrocytes and were probed, in Western blots, with a PfEMP1-specific antibody raised against a conserved sequence of the acidic terminal segment. A, Isolates selected for adhesion to CSA (CS2, HCS3, and 3D7-CSA). Each isolate appears to express a single dominant form of PfEMP1 with a similar molecular weight (∼300 kDa; SDS-PAGE performed with Tris-acetate buffer on 3%-8% gradient gel). B, Labeling of PfEMP1 bands of different relative molecular masse with extracts from the CS2 isolate, compared with isolate E8B, which adheres to CD36 and intercellular adhesion molecule 1 (SDS-PAGE was performed with Tris-glycine buffer on 6% acrylamide gel). C, Labeling of multiple PfEMP1 bands in extracts from different placental isolates. Isolate CS2 was included for comparison (SDS-PAGE was performed with Tris-acetate buffer on 3%-8% gradient gel). Molecular weight markers (expressed in kilodaltons) appear to the left of each blot. No labeling of proteins was observed with extracts from uninfected erythrocytes (i.e., red blood cells [RBCs]).
Figure 2
Figure 2
Demonstration, on Western blots, of cleavage of Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) as a result of trypsin treatment (10 μg/mL for 15 min) of the surface of intact infected erythrocytes (IEs) that adhere to chondroitin sulfate A (CSA). Membrane-bound proteins were extracted from trypsin-treated and control IEs and were probed with a PfEMP1-specific antibody raised against a conserved sequence of the acidic terminal segment. Bands of lower relative molecular mass (Mr) that were labeled in the trypsin-treated samples (Tryp) were not observed in the control samples (Con). A, Yielding of 2 bands of low Mr by trypsin in both CS2 and HCS3. The Mr of the cleavage products also differed between the 2 isolates. An additional lane for HCS3 (far right; Con) is shown at reduced exposure to reveal the position of the major high-molecular-weight band. B, Detection of only 1 additional band in 3D7-CSA in trypsin-treated samples. This band was of lower Mr than were bands detected in CS2. An additional lane for 3D7-CSA (far right; Con) is shown at reduced exposure, to reveal the position of the major high-molecular-weight band. No labeling of proteins was observed with extracts from uninfected erythrocytes (i.e., red blood cells [RBCs]). Molecular weight markers (expressed in kilodaltons) appear to the left of the blots. SDS-PAGE was performed with Tris-acetate buffer (3%-8% gradient gel).
Figure 3
Figure 3
Differences between isolates in adhesion to chondroitin sulfate A (CSA) after trypsin treatment of the surface of intact infected erythrocytes (IEs), as well as differences in the inhibition of adhesion of isolates by antiserum. A, Effect of trypsin treatment of CS2, HCS3, and 3D7-CSA IEs on adhesion to CSA. Adhesion of CS2 IEs was largely resistant to trypsin, whereas adhesion of HCS3 IEs was highly sensitive to trypsin at all concentrations. 3D7-CSA was partially inhibited at a trypsin concentration of 10 μg/mL and was inhibited >90% at a concentration of 100 μg/mL. Values expressed relative to adhesion of control-treated IEs are the mean ± SEM of 2 experiments performed in triplicate. B, Effect of rabbit antiserum raised against CS2 IEs on adhesion of CS2 and HCS3 IEs to CSA. The CS2 antiserum completely inhibited adhesion of CS2 IEs at 1:10 and 1:20 dilution, whereas there was little inhibition of adhesion of HCS3 IEs. Values expressed relative to adhesion using control rabbit serum are the mean ± SEM of 2 experiments performed in triplicate. Differences between inhibition of CS2 and HCS3 IEs were statistically significant at all serum dilutions (P < .01, Wilcoxon rank-sum test).
Figure 4
Figure 4
Distinct and overlapping reactivity to different chondroitin sulfate A (CSA)-binding isolates by serum samples obtained from pregnant women. Binding of IgG to the surface of CS2-, HCS3-, and 3D7-CSA-infected erythrocytes (IEs) was determined using immunofluorescence with flow cytometry. All isolates were tested against the same panel of serum samples obtained from primigravid Malawian women. IgG binding is expressed as a ratio of the fluorescence of IEs to the fluorescence of uninfected erythrocytes. A relative score of 1, denoted by broken lines in the charts, indicates that no significant IgG binding to IEs was detected, compared with uninfected erythrocytes. Correlations are as follows: r = 0.839 and P < .001 for CS2 and 3D7-CSA (top; n = 46); r = 0.837 and P < .001 for CS2 and HCS3 (middle; n = 47); and r = 0.792 and P < .001 for HCS3 and 3D7-CSA (bottom; n = 46).
Figure 5
Figure 5
Isolate specificity and overlap in adhesion inhibitory activity and agglutinating antibodies for CS2, HCS3, and placental isolates among serum samples obtained from pregnant women. A, Representative example of the correlation between the inhibitory effect of samples on adhesion to chondroitin sulfate A (CSA) of CS2- vs. HCS3-infected erythrocytes (IEs) (samples from primigravid women were obtained at delivery; r = 0.42; P = .058). B, Inhibition of adhesion of CS2 and HCS3 IEs to CSA by serum samples obtained from multigravidae (MG) and primigravidae (PG) during the second trimester; values are the mean of 2 experiments performed in duplicate, and they are expressed relative to values for control samples. The gravidity of the donors is indicated below the X-axis. C, Antibodies to CSA-binding isolates CS2 and HCS3 in the serum samples obtained from pregnant women, as measured by agglutination. Data show the proportion of serum samples positive to CS2 only, to HCS3 only, or to both. A greater proportion of secundigravidae (SG) and MG had antibodies to both isolates, compared with PG (P < .05, χ2 test). The proportion of serum samples that were negative for both isolates was 50%, 33%, and 44% for PG, SG, and MG, respectively. D, Effect of serum samples obtained from pregnant women on the adhesion to CSA of IEs from isolate CS2 and a placental isolate. Gravidity of the donors is indicated below the X-axis. neg, negative; pos, positive.
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References

    1. Walter PR, Garin Y, Blot P. Placental pathologic changes in malaria: a histologic and ultrastructural study. Am J Pathol. 1982;109:330–42. - PMC - PubMed
    1. Beeson JG, Amin N, Kanjala M, Rogerson SJ. Selective accumulation of mature asexual stages of Plasmodium falciparum-infected erythrocytes in the placenta. Infect Immun. 2002;70:5412–5. - PMC - PubMed
    1. Fried M, Duffy PE. Adherence of Plasmodium falciparum to chondroitin sulfate A in the human placenta. Science. 1996;272:1502–4. - PubMed
    1. Beeson JG, Brown GV, Molyneux ME, Mhango C, Dzinjalamala F, Rogerson SJ. Plasmodium falciparum isolates from infected pregnant women and children are associated with distinct adhesive and antigenic properties. J Infect Dis. 1999;180:464–72. - PMC - PubMed
    1. Beeson JG, Rogerson SJ, Cooke BM, et al. Adhesion of Plasmodium falciparum-infected erythrocytes to hyaluronic acid in placental malaria. Nat Med. 2000;6:86–90. - PMC - PubMed

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