Comparative analysis of the Plasmodium falciparum histidine-rich proteins HRP-I, HRP-II and HRP-III in malaria parasites of diverse origin

• Published in: Parasitology Vol. 95 ( Pt 2); p. 209
• Main Authors: Rock, E P, Marsh, K, Saul, A J, Wellems, T E, Taylor, D W, Maloy, W L, Howard, R J
• Format: Journal Article
• Language: English
• Published: England 01.10.1987
• Subjects: Adult; Animals; Antibodies, Monoclonal - immunology; Electrophoresis, Polyacrylamide Gel; Erythrocytes - parasitology; Female; Fluorescent Antibody Technique; Glycoproteins - analysis; Glycoproteins - immunology; Humans; Immune Sera - immunology; Immunoassay; Plasmodium falciparum - analysis; Plasmodium falciparum - immunology; Plasmodium malariae - analysis; Plasmodium malariae - immunology; Proteins - analysis; Proteins - immunology
• ISSN: 0031-1820
• DOI: 10.1017/S0031182000057681

Plasmodium falciparum-infected erythrocytes (IRBC) synthesize 3 histidine-rich proteins: HRP-I or the knob-associated HRP, HRP-II and HRP-III or SHARP. In order to distinguish these proteins immunochemically we prepared monoclonal antibodies which react with HRP-I, HRP-II and HRP-III, and rabbit antisera against synthetic peptides derived from the HRP-II and HRP-III sequences. A comparative analysis of diverse P. falciparum parasites was made using these antibodies and immunoprecipitation or Western blotting. HRP-I (Mr 80,000-115,000) was identified in all knob-positive P. falciparum parasites including isolates examined directly from Gambian patients. However, this protein was of lower abundance in these isolates and in 6 knob-positive, culture-adapted parasites compared to Aotus monkey-adapted parasites or culture-adapted parasites studied previously. HRP-II (Mr 60,000-105,000) was identified in all P. falciparum parasites regardless of knob-phenotype, and was recovered from culture supernatants as a secreted water-soluble protein. Within IRBC, HRP-II was found as a complex of several closely spaced bands. Cell surface radio-iodination of IRBC from several isolates and immunoprecipitation with a rabbit antiserum against the HRP-II repeat sequence identified HRP-II as a surface-exposed protein. Like HRP-I, the abundance of HRP-II was lower in the Gambian isolates than with Aotus monkey-adapted parasites studied earlier. Neither HRP-I nor HRP-II were identified in a knob-positive isolate of P. malariae collected from a Gambian patient. Analogues of these HRP were also absent from asexual parasites of diverse primate and murine malaria species screened with this panel of antibodies. HRP-III (Mr 40,000-55,000) was distinguished by its lower apparent size and by specific reaction with rabbit antibody against its 5-mer repeat sequence. HRP-III was of lowest abundance compared with the other two HRP. These antibody reagents and distinguishing properties should prove useful in studies on the separate functions of the 3 P. falciparum HRP.