Induction of opsonizing antibodies after injection of recombinant Plasmodium falciparum vaccine candidate antigens in preimmune Saimiri sciureus monkeys

Abstract

We have previously shown that Plasmodium falciparum recombinant antigens PfEB200, R23, and Pfi72 inhibit opsonization of infected erythrocytes by hyperimmune Saimiri sera, indicating that they contain target epitopes involved in the phagocytosis of infected erythrocytes. We have investigated in this study the immune response of Saimiri monkeys with previous experience of malaria infections (preimmune monkeys) after injection of these recombinant antigens, administered alone or simultaneously. The humoral response to the recombinant antigens was monitored by radioimmunoassay, and the response to P. falciparum blood stages was assayed by immunofluorescence. The relative proportion of protective versus nonprotective immunoglobulin subtypes was investigated by using 3A2/G6 and 3E4/H8 monoclonal antibodies, and the capacity of the antisera to promote in vitro phagocytosis of infected erythrocytes was evaluated. The antigens evoked in most cases a secondary-type antibody response, resulting in important increases in antigen-specific antibody titers and concomitantly in anti-P. falciparum titers. The ratio of 3A2/G6 to 3E4/H8 immunoglobulin subtypes varied with the immunogen used. Opsonizing antibodies were boosted in several animals, the most promising combination being the mixture of PfEB200 and R23 that induced long-lasting production in five of five animals. The detectable opsonizing activity appearing after immunization of the animals was antigen specific, as it was lost after adsorption of the recombinant antigens. The challenge of the animals with blood stage parasites confirmed previous findings showing a correlation between the presence of detectable opsonizing antibodies in serum and protection.

Immunity to asexual blood stage malaria and vaccine approaches

“…Parasite antigen‐specific Ab play an important role in controlling parasitaemia via Ab‐dependent cellular inhibition (ADCI), whereby binding of antibodies to phagocytes via Fc receptors leads to inhibition of parasite growth 13 , 26 , 32 , 33 . It has been demonstrated that specific Ab initiate parasite clearance by opsonization, thus enhancing the activity of phagocytic cells 34 or initiating complement‐mediated damage 35 , 36 . Merozoite surface protein 1 19 ‐specific Ab not only inhibit secondary processing of the MSP1 precursor 37 but also bind to MSP1 19 , thus preventing the merozoite from binding to the RBC surface 38 (see below).…”

Limited genetic diversity of Plasmodium falciparum in field isolates from Honduras.

“…One such antigen is Pf332, which is associated with the membrane of the trophozoite-and schizont-infected red blood cells and in the very late stages is exposed on the surface of the erythrocyte, 13 thus becoming an accessible target for opsonizing antibodies. [14][15][16][17] Previous studies have demonstrated a marked diversity by RFLP in the Pf332 gene from different parasite isolates. 3,18,19 Within the Pf332 locus, we examined size variability of a distinct region corresponding to a 498-basepair (bp) sequence that encodes repetitive, degenerate 11-mer amino acid sequences.…”

Breaking the Non‐Responsiveness of C57BL/6 Mice to the Malarial Antigen EB200 – The Role of Carrier and Adjuvant Molecules

“…Protein expression and purification. The recombinant EB200 was expressed as a fusion protein with GST in the pGEX vector (kindly provided by Dr Denise Mattei, Pasteur Institute, Paris, France) [2] using Escherichia coli strain RR1DM15 as the bacterial host. PGEXEB200transformed E. coli cells were cultured overnight (ON) at 37 C in Luria-Bertani (LB) medium supplemented with yeast extract and 100 mg/ml of ampicillin (Sigma, St. Louis, MO, USA) and the protein was induced for 4 h at 37 C with 0.2 mM isopropyl-b-thiogalactosidase (Saveen Biotech AB, Stockholm, Sweden).…”

“…A fragment of Pf332, termed EB200, fulfils a number of criteria for a vaccine candidate antigen. Immunization of squirrel monkeys with EB200 conferred partial protection against a P. falciparum challenge [2], and EB200 is immunogenic in humans [3]. However, in mice, EB200 exerts an MHC-restricted response [4] which is a drawback for creating a universal vaccine based on this antigen if the same limitation occurs in humans.…”