Characterization of an S antigen synthesized by several isolates of Plasmodium falciparum.

Abstract

The S antigen of a Papua New Guinean isolate of Plamodium falciparum was identified by immunoblotting as the dominant antigen in culture supernatants. An antigen identical in molecular weight (Mr 220,000), isoelectric point (pI 4.2), and immunoreactivity with sera from individuals exposed to malaria was expressed by four Papua New Guinean isolates and one isolate of unknown origin. The Mr 220,000 antigen was not detected in culture supernatants derived from two isolates from Thailand and one from Ghana. The Mr 220,000, pI 4.2 S antigen may characterize a subpopulation of parasites common to many isolates of P. falciparum, which is selected for by continuous culture in vitro A variant S antigen, 30 kilodaltons larger but with similar immunoreactivity, was expressed by 1 of 26 clonal populations derived by limit-dilution culture from one of the Papua New Guinean isolates of P. falciparum. The characteristics of the S antigen, defined by immunoblotting, allowed it to be identified in two-dimensional separations of [mS]methionine-labeled parasite proteins, thus confirming the parasite origin of the antigen.Plasmodiumfalciparum, the major cause of morbidity and mortality in malaria infections of man, exhibits considerable antigenic heterogeneity, which may be a major problem in developing an effective vaccine against malaria. The most extensive studies of antigenic heterogeneity in P. falciparum have concerned a system of soluble heat-stable antigens known as the S antigens. The S antigens were first demonstrated in extracts of infected placentas but are also found in the sera of some infected individuals. The S antigens, which have been the subject of a series of detailed studies by Wilson and colleagues (1-9), have the following characteristics: (i) stability to heating at 100°C for 5 min; (ii) serological complexity with individual isolates expressing more than one specificity; (iii) poor immunogenicityno heterologous antiserum has been produced and there is a marked age-dependent acquisition of antibodies in man; (iv) presence in the medium when P. falciparum is maintained in culture in vitro; and (v) molecular weight and charge heterogeneity.Techniques such as two-dimensional gel electrophoresis of biosynthetically labeled immunoprecipitates (10) and immunofluorescence with monoclonal antibodies (11) have provided new approaches to the direct demonstration of antigenic heterogeneity in P. falciparum. However, these techniques have not been directly applied to an analysis of the S antigens. A major limitation to the more detailed analysis of S antigens has been the failure to label the antigens with radioactive metabolites (12). Thus, to date, analyses of the S antigen have been dependent on relatively insensitive gel precipitation techniques and have been restricted to sources in which antibodies and antigens are sufficiently abundant to give visible precipitates.To circumvent the apparent problems of biosynthetic labeling S antigens, we have used the technique of "immunoblotting" to identify the pre...

Antibodies in malarial sera to parasite antigens in the membrane of erythrocytes infected with early asexual stages of Plasmodium falciparum.

“…The soluble supernatant antigens eluted from insolubilized antibodies of a hyperimmune Liberian serum were the most effective inhibitor of all those tested. Moreover, this inhibition was heat resistant, suggesting that the inhibitory antigens may be related to the S antigens, a serologically complex family of soluble, parasite-derived antigens of different molecular weights present both in patient sera and in supernatants of P. falciparum cultures (27,33,34).…”

Transcriptional variation in the malaria parasitePlasmodium falciparum

“…Clonal parasite lines 3D7, 7G8, D10, and HB3 have been previously described (Anders et al 1983;Burkot et al 1984;Walliker et al 1987). 3D7 stocks 3D7-A and 3D7-B, and 3D7-A subclones have also been described before (Cortés et al 2004(Cortés et al , 2007Cortés 2005).…”

Subtelomeric chromosome deletions in field isolates of Plasmodium falciparum and their relationship to loss of cytoadherence in vitro.

“…Trophozoite-rich parasite preparations were separated by sodium dodecyl sulfate/polyacrylamide gel electrophoresis and transferred to nitrocellulose filters. Filters were probed with affinity-purified human antibodies to the knob-associated histidine-rich protein (KAHRP) (18) or S antigen (19) as described (20).…”