ABSTRACT
BACKGROUND: The use of prophylactic antisepsis to protect against coronavirus disease 2019 (COVID-19) has been suggested. This study investigated hydrogen peroxide antisepsis (HPA) at two hospitals in Ghana. METHODS: Cases of COVID-19 among healthcare workers (HCWs) using hydrogen peroxide (HP-HCWs) or not using hydrogen peroxide (NHP-HCWs), vaccinated or unvaccinated, were recorded at Shai-Osudoku Hospital (SODH), Dodowa, and Mount Olives Hospital (MOH), Techiman, between May 2020 and December 2021. The effect of HPA in all inpatients at MOH was also observed. Permutation tests were used to determine P values. FINDINGS: At SODH, there were 62 (13.5%) cases of COVID-19 among 458 NHP-HCWs but no cases among eight HP-HCWs (P=0.622) from May to December 2020. Between January and March 2021, 10 (2.7%) of 372 NHP-HCWs had COVID-19, but there were no cases among 94 HP-HCWs (P=0.206). At MOH, prior to HPA, 17 (20.2%) of 84 HCWs and five (1.4%) of 370 inpatients had COVID-19 in July 2020. From August 2020 to March 2021, two of 54 (3.7%) HCWs who stopped HPA had COVID-19; none of 32 NHP-HCWs contracted COVID-19. At SODH, none of 23 unvaccinated HP-HCWs and 35 (64%) of 55 unvaccinated NHP-HCWs had COVID-19 from April to December 2021 (P<0.0001). None of 34 vaccinated HP-HCWs and 53 (13.6%) of 390 vaccinated NHP-HCWs had COVID-19 (P=0.015). No inpatients on prophylactic HPA (total 7736) contracted COVID-19. CONCLUSION: Regular, daily HPA protects HCWs from COVID-19, and curtails nosocomial spread of SARS-CoV-2.
Subject(s)
COVID-19 , Antisepsis , COVID-19/prevention & control , Health Personnel , Humans , Hydrogen Peroxide , SARS-CoV-2ABSTRACT
A crude acetone/water (50/50) extract of neem leaves (IRAB) was evaluated for activity against the asexual (trophozoites/schizonts) and the sexual (gametocytes) forms of the malarial parasite, Plasmodium falciparum, in vitro. In separate 72 hour cultures of both asexual parasites and mature gametocytes treated with IRAB (0.5 microg/mL), parasite numbers were less than 50% of the numbers in control cultures, which had 8.0% and 8.5% parasitemia, respectively. In cultures containing 2.5 microg/mL, asexual parasites and mature and immature gametocytes were reduced to 0.1%, 0.2%, and 0% parasitemia, respectively. There were no parasites in the cultures containing 5.0 microg/mL. This extract, if found safe, may provide materials for development of new antimalarial drugs that may be useful both in treatment of malaria as well as the control of its transmission through gametocytes.
Subject(s)
Antimalarials/pharmacology , Azadirachta , Plasmodium falciparum/drug effects , Animals , Cells, Cultured , Dose-Response Relationship, Drug , Gametogenesis/drug effects , Plant Extracts/pharmacology , Plant Leaves/chemistry , Plasmodium falciparum/physiology , Reproduction/drug effects , Schizonts/drug effectsABSTRACT
To determine which species and populations of Anopheles transmit malaria in any given situation, immunological assays for malaria sporozoite antigen can replace traditional microscopical examination of freshly dissected Anopheles. We developed a wicking assay for use with mosquitoes that identifies the presence or absence of specific peptide epitopes of circumsporozoite (CS) protein of Plasmodium falciparum and two strains of Plasmodium vivax (variants 210 and 247). The resulting assay (VecTest Malaria) is a rapid, one-step procedure using a 'dipstick' test strip capable of detecting and distinguishing between P. falciparum and P. vivax infections in mosquitoes. The objective of the present study was to test the efficacy, sensitivity, stability and field-user acceptability of this wicking dipstick assay. In collaboration with 16 test centres world-wide, we evaluated more than 40 000 units of this assay, comparing it to the standard CS ELISA. The 'VecTest Malaria' was found to show 92% sensitivity and 98.1% specificity, with 97.8% accuracy overall. In accelerated storage tests, the dipsticks remained stable for > 15 weeks in dry conditions up to 45 degrees C and in humid conditions up to 37 degrees C. Evidently, this quick and easy dipstick test performs at an acceptable level of reliability and offers practical advantages for field workers needing to make rapid surveys of malaria vectors.
Subject(s)
Anopheles/immunology , Anopheles/parasitology , Antigens, Protozoan/immunology , Insect Vectors/immunology , Insect Vectors/parasitology , Plasmodium falciparum/immunology , Plasmodium vivax/immunology , Reagent Strips/standards , Animals , Enzyme-Linked Immunosorbent Assay , Malaria, Falciparum/transmission , Malaria, Vivax/transmission , Protozoan Proteins/immunology , Sensitivity and Specificity , Time FactorsABSTRACT
Direct automated DNA sequencing was used to analyze exons 2 and 3 of HLA-B alleles present in forty-four unrelated individuals residing in the village of Adiopodoume, Côte d'Ivoire (Ivory Coast). Of the 23 HLA-B alleles observed, the most frequently detected allele was HLA-B*5301 (22.7%), which is believed to confer resistance to severe Plasmodium falciparum malaria. B*4501 (9.1%), B*1503 (8.0%), B*0705 (5.7%), B*1510 (5.7%) and B*3501 (5.7%) occurred frequently in the population. A second allele of B53 was identified; B*5302 contains a single amino acid variation at residue 171 (Y-->H). Two additional novel alleles, B* 1405 (a single amino acid variant of B*1402) and B*4410 (a five amino acid variant of B*4403) were characterized.
Subject(s)
Alleles , Gene Frequency/immunology , HLA-B Antigens/genetics , Sequence Analysis, DNA , Base Sequence , Cote d'Ivoire , HLA Antigens , HLA-B14 Antigen , HLA-B44 Antigen , Humans , Molecular Sequence Data , Sequence Analysis, DNA/methodsABSTRACT
To examine the genetic diversity in west Africa, class I HLA-A and HLA-B alleles of 92 unrelated individuals from two areas in the Cameroon, the capital Yaoundé and the village of Etoa, were identified by direct automated DNA sequencing of exons 2 and 3 of the HLA-B locus alleles and sequence-specific oligonucleotide probe (SSOP) and/or sequencing of the HLA-A locus alleles. HLA-A*2301 (18.7%), A*2902 (10.4%), B*5301 (10.9%), and B*5802 (10.9%) were the most frequently detected alleles, present in at least 10% of the population. A total of 30 HLA-A locus and 33 HLA-B locus alleles, including six novel alleles, were detected. The novel alleles were HLA-A*03012, A*2612, A*3006 and HLA-B*1403, B*4016, and B*4703. HLA-B*4703 contains a novel amino acid sequence that is a combination of the first 5 amino acids of the Bw6 epitope and the last 2 residues of the Bw4 epitope. The addition of 6 alleles to the ever-expanding number of known class I HLA alleles supports our hypothesis that extensive genetic diversity, including previously undescribed alleles, would be observed in this African population. In the Yaoundé population, the allele frequency distribution at the HLA-A locus is consistent with distributions indicative of balancing selection. Extensive HLA-A-B haplotypes were observed in this population suggesting that only a fraction of the Cameroon HLA-A-B haplotype diversity has been observed.
Subject(s)
Genetic Variation , HLA-A Antigens/genetics , HLA-B Antigens/genetics , Alleles , Base Sequence , Cameroon , HLA-A Antigens/immunology , HLA-B Antigens/immunology , Humans , Molecular Sequence DataABSTRACT
Vaccines for P. falciparum will need to contain both T- and B-cell epitopes. Conserved epitopes are the most desirable, but they are often poorly immunogenic. The major merozoite surface protein 1 (MSP-1) is currently a leading vaccine candidate antigen. In this study, six peptides from conserved or partly conserved regions of MSP-1 were evaluated for immunogenicity in B10 congenic mice. Following immunization with the peptides, murine T cells were tested for the ability to proliferate in vitro and antibody responses to MSP-1 were evaluated in vivo. The results showed that one highly conserved sequence (MSP-1#1, VTHESYQELVKKLEALEDAV; located at amino acid positions 20 to 39) and one partly conserved sequence (MSP-1#23, GLFHKEKMILNEEEITTKGA; located at positions 44 to 63) contained both T- and B-cell epitopes. Immunization of mice with these peptides resulted in T-cell proliferation and enhanced production of antibody to MSP-1 upon exposure to merozoites. MSP-1#1 stimulated T-cell responses in three of the six strains of mice evaluated, whereas MSP-1#23 was immunogenic in only one strain. Immunization with the other four peptides resulted in T-cell responses to the peptides, but none of the resulting peptide-specific T cells recognized native MSP-1. These results demonstrate that two sequences located in the N terminus of MSP-1 can induce T- and B-cell responses following immunization in a murine model. Clearly, these sequences merit further consideration for inclusion in a vaccine for malaria.
Subject(s)
Conserved Sequence/immunology , Epitopes, B-Lymphocyte/immunology , Epitopes, T-Lymphocyte/immunology , Merozoite Surface Protein 1/immunology , Plasmodium falciparum/immunology , Protozoan Vaccines/immunology , Vaccines, Synthetic/immunology , Amino Acid Sequence , Animals , Antibodies, Protozoan/biosynthesis , Cell Division , Epitope Mapping , Female , H-2 Antigens/immunology , Histocompatibility Antigen H-2D , Humans , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Molecular Sequence Data , Peptides/immunology , T-Lymphocytes/cytology , T-Lymphocytes/immunology , T-Lymphocytes/parasitology , VaccinationABSTRACT
The Plasmodium falciparum rhoptry-associated proteins 1 and 2 (RAP1 and RAP2) are candidate antigens for a subunit malaria vaccine. The design of the study, which looks at the acquisition of immunity to malaria from childhood to old age, has allowed us to document the interaction of HLA and age on levels of antibody to specific malarial antigens. Antibodies reach maximum levels to RAP1 after the age of 15 but to RAP2 only after the age of 30. The effect of HLA-DRB1 and -DQB1 and age on levels of antibody to rRAP1 and rRAP2 was analyzed with a multiple regression model in which all HLA alleles and age were independent variables. DQB1*0301 and -*03032 showed an age-dependent association with levels of antibody to rRAP1, being significant in children 5 to 15 years (P < 0.001) but not in individuals over 15 years of age. DRB1*03011 showed an age-dependent association with antibody levels to rRAP2; however, this association was in adults over the age of 30 years (P < 0.01) but not in individuals under the age of 30 years. No associations were detected between DRB1 alleles and RAP1 antibody levels or between DQB1 alleles and RAP2 antibody levels. Thus, not only the HLA allele but also the age at which an interaction is manifested varies for different malarial antigens. The interaction may influence either the rate of acquisition of antibody or the final level of antibody acquired by adults.
Subject(s)
Antibodies, Protozoan/immunology , HLA-DQ Antigens/metabolism , HLA-DR Antigens/metabolism , Plasmodium falciparum/immunology , Protozoan Proteins/immunology , Adolescent , Adult , Age Factors , Aged , Alleles , Animals , Child , Child, Preschool , Enzyme-Linked Immunosorbent Assay , HLA-DRB1 Chains , Hemoglobin, Sickle/genetics , Hemoglobin, Sickle/immunology , Humans , Immunity , Malaria, Falciparum/genetics , Malaria, Falciparum/immunology , Middle Aged , Polymorphism, Genetic , Protozoan Proteins/blood , Recombinant Proteins/immunologyABSTRACT
In support of ongoing immunologic studies on immunity to Plasmodium falciparum, demographic, entomologic, parasitologic, and clinical studies were conducted in two Cameroonian villages located 3 km apart. Simbok (population = 907) has pools of water present year round that provide breeding sites for Anopheles gambiae, whereas Etoa (population = 485) has swampy areas that dry up annually in which A. funestus breed. Results showed that individuals in Simbok receive an estimated 1.9 and 1.2 infectious bites per night in the wet and dry season, respectively, whereas individuals in Etoa receive 2.4 and 0.4 infectious bites per night, respectively. Although transmission patterns differ, the rate of acquisition of immunity to malaria appears to be similar in both villages. A prevalence of 50-75% was found in children < 10 years old, variable levels in children 11-15 years old, and 31% in adults. Thus, as reported in other parts of Africa, individuals exposed to continuous transmission of P. falciparum slowly acquired significant, but not complete, immunity.
Subject(s)
Anopheles/parasitology , Malaria, Falciparum/epidemiology , Malaria, Falciparum/immunology , Plasmodium falciparum/isolation & purification , Adolescent , Adult , Age Distribution , Aged , Animals , Anopheles/classification , Cameroon/epidemiology , Child , Child, Preschool , Disease Vectors , Female , Humans , Infant , Infant, Newborn , Longitudinal Studies , Malaria, Falciparum/transmission , Male , Middle Aged , Plasmodium falciparum/immunology , Plasmodium falciparum/parasitology , Prevalence , SeasonsABSTRACT
To identify B-cell epitopes of the Plasmodium falciparum 25-kDa ookinete protein, Pfs25, 41 overlapping synthetic peptides spanning the entire length of the protein were used individually to immunize CAF1 (F1 hybrid of BALB/c female and A/J male) mice. Antipeptide sera were tested for reactivity to live intact zygote/early ookinete (post-fertilization stage) by immunofluorescence, and by Western blot analysis under nonreducing and reducing conditions, immunoprecipitation of 35S-cysteine-labeled antigen, and ELISA using a vaccinia recombinant Pfs25 antigen. Fourteen B-cell epitopes were identified. These peptides were immunogenic only when administered with high-dose recombinant interleukin-2. Antibodies to 11 peptides recognized only the native conformational structure, one peptide induced antibodies that recognized both reduced and native protein, and two other peptides, after primary immunization, made antibodies to denatured Pfs25, but after boosting the antibodies reacted to both denatured and native Pfs25. Anti-sera to peptides in the first (peptide 7) and fourth (peptide 34) epidermal growth factor-like domains of Pfs25 reacted most strongly with zygotes/ookinetes by immunofluorescence assay. The antibodies elicited by immunization with peptide 34 suppressed infectivity of the parasite to mosquitoes. We further observed that the secondary structure of Pfs25 may be important for immunogenicity because monoclonal antibodies (MAbs) 1C7 and 1D2, both transmission-blocking MAbs, protected enzyme cleavage sites in Pfs25 from proteolysis, suggesting that discontinuous segments of Pfs25 may come together to form immunogenic epitopic sites. Thus, definition of B- and T-cell epitopes may be required to construct a Pfs25 vaccine for optimum immunogenicity.
Subject(s)
Antibodies, Protozoan/immunology , Interleukin-2/pharmacology , Peptide Fragments/immunology , Plasmodium falciparum/immunology , Protozoan Proteins/chemistry , Protozoan Proteins/immunology , Amino Acid Sequence , Animals , Antibodies, Monoclonal , Epitopes/chemistry , Epitopes/immunology , Female , Humans , Immunization , Male , Mice , Mice, Inbred A , Mice, Inbred BALB C , Molecular Sequence Data , Peptide Fragments/chemistry , Plasmodium falciparum/chemistry , Protein Conformation , Recombinant Proteins/pharmacologyABSTRACT
T cells are thought to be of central importance in malaria immunity. Peptides copying malaria protein sequences often stimulate human CD4+ T cells and it was thought that they represented T cell epitopes present in the parasite and may thus have particular relevance to malaria vaccine development. To verify whether synthetic peptides representing highly conserved regions of parasite Ags may contribute to a malaria vaccine, we searched the data bank for conserved regions of Plasmodium falciparum malaria proteins that were not homologous to known self (human) proteins. We synthesized 24 such peptides representing 11 of the cloned and sequenced malaria asexual stage Ags, which were predicted by algorithms to represent T cell epitopes, and 6 peptides not predicted to be T cell epitopes and used these to generate T cell clones from individuals with an extensive previous history of malaria exposure. The T cell clones responded vigorously to many peptides but only a single clone, specific for a peptide within merozoite surface protein-1, 20-39, VTHESYQELVKKLEALEDAV, and not previously defined to be a T cell epitope responded to malaria parasites by proliferation and secretion of IFN-gamma. This epitope was not revealed by studying parasite-induced T cell lines and is thus subdominant. The clone was able to significantly inhibit parasite growth in vitro. The final step in the inhibition of parasite growth appears to be nonspecific because other activated clones (not specific for malaria sequences) can inhibit parasite growth. Our data suggest that few conserved peptides within malaria parasites can be processed from the intact parasite. However, such peptides that can be processed from malaria parasites may be expected to stimulate parasite-specific T cells that could inhibit parasite growth and as such may be lead candidates for a vaccine aimed at inducing cellular immunity to malaria.
Subject(s)
Antigens, Protozoan/immunology , Plasmodium falciparum/immunology , Protozoan Proteins/immunology , T-Lymphocytes/immunology , Adult , Aged , Amino Acid Sequence , Animals , Antigens, Protozoan/chemistry , Clone Cells , Female , Humans , Interferon-gamma/biosynthesis , Lymphocyte Activation , Male , Middle Aged , Molecular Sequence Data , Peptides/chemistry , Peptides/immunology , Protozoan Proteins/chemistryABSTRACT
We have defined a strategy for the development of a T-cell vaccine for blood stage immunity, taking into consideration the central role of T cells and MHC restriction in malaria immune responses. We have used the AMPHI computer algorithm to identify putative T-cell epitopes from conserved regions of 11 Plasmodium falciparum asexual stage proteins. Ten of the eleven proteins are currently candidates for vaccine development. Using this algorithm we selected 22 putative T-cell epitope peptides and 8 control peptides. These peptides were used to test the T-cell responses of three defined populations of Caucasians who have (1) recovered from P. falciparum malaria, (2) been exposed, but never clinically infected, (3) never been exposed or infected. Preliminary analysis of our data shows population differences in T-cell responses to putative T-cell epitope peptides. Ultimately, these studies will help to identify those T epitopes that can be incorporated into a T-cell vaccine for protective immunity.
Subject(s)
Plasmodium/immunology , Protozoan Vaccines/immunology , T-Lymphocytes/immunology , Animals , Epitopes , Humans , Major Histocompatibility Complex , Malaria/prevention & controlABSTRACT
Malarial infections are rarely observed in neonates. It has been postulated that some immunity may be passively transferred during nursing, but anti-malarial antibodies (Abs) have not been detected in human milk. In this study, milk samples, collected 2-14 days after parturition from women at the Central Maternity Hospital, Yaounde, were evaluated for total IgG and IgA antibody levels by radial diffusion, protein composition by SDS-PAGE, anti-malarial antibodies using an isotype-specific immunofluorescence assay, and the ability to immunoprecipitate Plasmodium falciparum antigens metabolically labelled with 35S-methionine. Results showed that anti-P. falciparum antibodies were present in breast milk, and that paired milk and serum samples from individual women contained Abs that recognized similar malarial antigens.
Subject(s)
Antibodies, Protozoan/analysis , Milk, Human/immunology , Plasmodium falciparum/immunology , Adolescent , Adult , Animals , Female , Humans , Immunoglobulin A/analysis , Immunoglobulin G/analysis , Immunoglobulin M/analysisABSTRACT
Pfs25 is a sexual stage antigen of Plasmodium falciparum that is expressed on the surface of zygote and ookinete forms of the parasite. Monoclonal antibodies directed against native Pfs25 can block completely the development of P. falciparum oocysts in the midgut of the mosquito vector. Thus, this 25-kD protein is a potential vaccine candidate for eliciting transmission-blocking immunity in inhabitants of malaria endemic regions. We have synthesized, by secretion from yeast, a polypeptide analogue of Pfs25 that reacts with conformation-dependent monoclonal antibodies, and elicits transmission-blocking antibodies when used to immunize mice and monkeys in conjunction with a muramyl tripeptide adjuvant. Our results suggest the further evaluation of recombinant DNA-derived Pfs25 in transmission-blocking vaccination studies in humans.
Subject(s)
Malaria, Falciparum/immunology , Plasmodium falciparum/immunology , Protozoan Proteins/immunology , Vaccines, Synthetic/immunology , Animals , Antibodies, Monoclonal/immunology , Antibodies, Protozoan/analysis , Antigens, Surface/immunology , Epidermal Growth Factor/immunology , Haplorhini , Immunization , Mice , Mice, Inbred BALB C , Protein Conformation , Protozoan Proteins/geneticsABSTRACT
Humans infected with Plasmodium falciparum frequently have elevated levels of proteins in their urine, but it is unclear if any of these proteins are parasite antigens or antimalarial antibodies. To resolve this question, urine samples from malaria patients and controls living in Thailand and Ghana were evaluated. Urine samples from 85% of the patients had elevated protein levels and contained proteins with Mrs ranging from less than 29,000 to greater than 224,000 as determined by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. Antisera were produced against urine from infected and control subjects. Antisera raised against infected, but not control, urine were positive by indirect immunofluorescence on P. falciparum parasites and immunoprecipitated approximately 12 unique bands from extracts of parasites metabolically labeled with 35S-methionine. These data suggest that a variety of P. falciparum antigens are released into urine during acute infection. It is also likely that anti-P. falciparum antibodies are present in the urine of malaria patients because samples from these patients, but not controls, were positive in indirect immunofluorescence assays and immunoprecipitated at least 19 P. falciparum antigens from extracts of metabolically labeled parasites. The detection of malarial antigens and antibodies in urine may lead to a new approach for the diagnosis of malaria.
Subject(s)
Antibodies, Protozoan/urine , Antigens, Protozoan/urine , Malaria/immunology , Plasmodium falciparum/immunology , Adult , Animals , Antigens, Protozoan/chemistry , Humans , Malaria/diagnosis , Malaria/urine , Molecular Weight , Protozoan Proteins/chemistry , Protozoan Proteins/immunology , Protozoan Proteins/urineABSTRACT
Monoclonal antibodies (MAbs) directed against different epitope regions on three sexual stage-specific gamete surface proteins of Plasmodium falciparum, Pfs 25, Pfs 230, and Pfs 48/45, were used to study the genetic diversity of these epitopes among fresh isolates of P. falciparum from Malaysia, using immunofluorescence microscopy (IFA). Among 45 Malaysian isolates, one epitope of Pfs 25, designated region I, showed evidence of variable reactivity with MAbs among different isolates; the Pfs 25 epitope, region II, was universally recognized by MAbs in all isolates. Two apparently distinct epitope regions of Pfs 230 were defined by MAbs, one of which was universally recognized by MAbs among the 45 isolates; the other was conserved in all but three isolates. The epitope regions of gamete-surface protein Pfs 48/45, designated regions I, IIa, IIb, IIc, III, and IV, were examined for reactivity by IFA in 33 isolates. Epitope regions I, IIb, III, and IV were conserved in all isolates; regions IIa and IIc existed in variant forms.
Subject(s)
Antigenic Variation , Antigens, Protozoan/immunology , Malaria/parasitology , Plasmodium falciparum/immunology , Protozoan Proteins/immunology , Adolescent , Adult , Animals , Antibodies, Monoclonal/immunology , Antibodies, Protozoan/immunology , Child , Child, Preschool , Epitopes/immunology , Humans , Malaysia , MaleABSTRACT
Many candidate antigens of malaria vaccines have limited immunological recognition. One exception is Pfs25, a cysteine-rich, 25-kilodalton sexual stage surface protein of Plasmodium falciparum. Pfs25 is a target of monoclonal antibodies that block transmission of malaria from vertebrate host to mosquito vector. The surface of mammalian cells infected with a recombinant vaccinia virus that expressed Pfs25 specifically bound transmission-blocking monoclonal antibodies. Furthermore, major histocompatibility complex-disparate congenic mouse strains immunized with recombinant Pfs25 elicited transmission-blocking antibodies, demonstrating that the capacity to develop transmission-blocking antibodies is not genetically restricted in mice. Live recombinant viruses may provide an inexpensive, easily administered alternative to subunit vaccines prepared from purified recombinant proteins to block transmission of malaria in developing countries.
Subject(s)
Antibodies, Protozoan/immunology , Malaria, Falciparum/prevention & control , Plasmodium falciparum/immunology , Protozoan Proteins/immunology , Vaccinia virus/immunology , Animals , Antibodies, Monoclonal/analysis , Antibodies, Monoclonal/immunology , Antigens, Protozoan , Immunization , Mice , Protozoan Proteins/genetics , Recombinant Proteins/immunology , Transfection , Vaccinia virus/geneticsABSTRACT
We have studied the properties of epitopes on Plasmodium falciparum gamete surface protein Pfs 48/45, a target antigen of malaria transmission blocking antibodies. Using a two site immunoradiometric assay we have defined three spacially separate, non-repeated, epitope regions on the peptides representing this antigen. Epitope region I is a target of monoclonal antibodies (MoAbs) which strongly suppress infectivity of gametocytes of P. falciparum to mosquitoes; the effect is complement independent and is mediated as effectively by the monovalent Fab fragments as by intact MoAb. Epitope region II consists of two spacially close subregions, IIa and IIb; variant forms of epitopes IIa and IIb occurred in different isolates of P. falciparum. Epitope region III also showed slight structural modification between isolates. MoAbs against regions II or III were relatively ineffective in suppressing gametocyte infectivity compared to MoAbs against region I. However, certain combinations of MoAbs against regions II and III together acted synergistically to suppress infectivity to mosquitoes. All these epitopes failed to react with MoAb when the antigen was presented in reduced form. A fourth epitope, however, was identified which reacted strongly with MoAb when the antigen was presented in reduced form. The MoAb against this epitope had no effect on the infectivity of gametocytes of P. falciparum to mosquitoes.
Subject(s)
Antibodies, Monoclonal/immunology , Antigens, Protozoan/immunology , Epitopes/immunology , Plasmodium falciparum/immunology , Animals , Antigens, Protozoan/analysis , Electrophoresis, Polyacrylamide Gel , Epitopes/analysis , Malaria/immunology , Malaria/prevention & control , Malaria/transmission , Membrane Proteins/immunology , Plasmodium falciparum/growth & development , Plasmodium falciparum/pathogenicity , Precipitin Tests , RadioimmunoassayABSTRACT
The circumsporozoite (CS) protein is a major candidate vaccine antigen for the sporozoite stage of malaria. Both cytotoxic T cells (CTL) and antibody specific for the CS protein are thought to be important in protection. By examining the immune response in mice and humans we have shown that genes mapping to the major histocompatibility complex (MHC) are important for immune responsiveness. F1 mice between high antibody responders and low antibody responders are high antibody responders, suggesting that in this model immune suppressor genes do not control the immune response. Using synthetic peptides to map epitopes for CTL and helper T cells (which are important for the antibody response) we have shown that the T-cell epitopes are located in the polymorphic region of the protein, and we hypothesize that T cells have indeed selected the variation observed in the CS protein. The success of subunit vaccines will depend on the pattern of variation in different geographical locations, the ability to construct multivalent vaccines containing different variant epitopes from this protein, and on the existence of other sporozoite and liver-stage proteins involved in protection.