Effects of immune pressure on parasite diversity

The overall aim of this project is to define mechanisms for P. falciparum parasites to evade neutralizing immune responses. The results generated in the project should provide new information of importance for a rational design of strategies for vaccine development. The project includes, on one hand, longitudinal studies with field isolates of parasites and immunoglobulins (Ig) from the same donors and, on the other hand, studies with established P. falciparum laboratory strains and antibodies to various vaccine candidate antigens. The specific objectives of the project are: -To analyse parasite neutralization in vitro of field isolates of P. falciparum in relation to parasite population dynamics and antigen expression; -To analyse the impact of the use of impregnated curtains on parasite neutralizing immune responses and on the complexity of infecting parasite populations; -To produce parasite neutralizing human monoclonal antibodies to conserved epitopes of different vaccine candidate antigens; -To analyse the effects of immune pressure exerted in vitro by antibodies on the growth and antigen expression of laboratory strains of P. falciparum.

Reference:
Bolad A and Berzins B: Antigenic diversity of Plasmodium falciparum and antibody-mediated parasite neutralization. 2000. Scand J Immunol 52, 233-239.

Evaluation of P. falciparum antigen Pf332 as a target for parasite neutralizing immune responses

This project is based on the P. falciparum antigen Pf332, which we identified in 1989 together with Mattei et al. at the Pasteur Institute in Paris. Subsequent data on Pf332, obtained mainly by our groups by laboratory experiments and epidemiological investigations, indicate that the antigen stands out as an attractive target for vaccine development. However, the previous research on Pf332 has involved mainly a 157 amino acids long fragment (EB200) of the antigen; the complete 5506 a.a. sequence became recently available from the sequencing of the P. falciparum genome. Due to the high degree of cross-reactivity of antibodies to EB200 with other P. falciparum antigens, it is difficult to deduce which antigen is the true target for them. This project will expand the studies on Pf332 to select new sequences in both the C- and N-terminal parts of the antigen, in order to evaluate it as a target for parasite neutralizing immune responses and its suitability as a vaccine component. The main objectives of the project are: - To define possible polymorphisms in Pf332; - To produce non-cross reactive antibodies to different parts of Pf332 and assessment of their parasite neutralizing activity; - To define epitopes in Pf332 which are targets for parasite neutralizing antibodies; - To analyze antibody responses to Pf332 in naturally primed individuals; - To analyze Pf332 synthesis, transport and location; - To design, construct and test the immunogenicity of nucleic acid-vaccines based on Pf332-epitopes.

Reference:
Adersson C, Vasconcelos N-M, Sievertzon M, Haddad D, Liljeqvist S, Berglund P, Liljeström P, Ahlborg N, Ståhl S and Berzins B: Comparative Immunization Study Using RNA and DNA constructs Encoding a Part of the Plasmodium falciparum Antigen Pf332. 2001. Scand J Immunol 54, 117-124.

A selection from Stockholm University publication database

• Associations of multi-locus polymorphisms in an immune network with susceptibility to uncomplicated Plasmodium falciparum malaria in Daraweesh village, Eastern Sudan

  2011. Hayder A. Giha (et al.). Infection, Genetics and Evolution 11 (7), 1674-1681

  Article

  Susceptibility to uncomplicated malaria (UM), as to other forms of the disease, is genetically determined. Over 9-years of clinical and parasitological follow up of inhabitants of Daraweesh, in Eastern Sudan, the relative susceptibility to UM was estimated in terms of number of episodes experienced by each individual. Previously, we reported that the levels of IgG2 and IgG3 to Pf332-C231 malaria antigen are negatively correlated with number of malaria episodes. In addition, four molecular markers for malaria susceptibility (CRP -286, GM/KM haplotypes, FcγRIIa131 and HbAS) were tested. In this study, the above data were combined and reanalysed. The CRP -286A allele and GM 1,17 5,13,14,6 phenotype were previously found to be associated with increased susceptibility to malaria; however, individuals have both polymorphism together were not more susceptible to UM than the non-carriers of the same double polymorphism. The FcγRIIa-RR131 and HbAA genotypes taken individually or as double polymorphism were not associated with malaria susceptibility; however, their combination with any or both of the former polymorphisms was mostly associated with increased susceptibility to malaria. None of the four markers were associated with the levels of IgG2 and IgG3 against Pf332-C231. In conclusion, while our data support the polygenic nature of susceptibility to UM and highlighted the role of immune markers polymorphisms, the combinations of these markers were not predictable, i.e. the combination of the susceptibility markers will not necessarily render the carriers more susceptible to UM.

  Read more about Associations of multi-locus polymorphisms in an immune network with susceptibility to uncomplicated Plasmodium falciparum malaria in Daraweesh village, Eastern Sudan

• Cytokine gene haplotypes with a potential effect on susceptibility to malaria in sympatric ethnic groups in Mali

  2011. Elisabeth Israelsson (et al.). Infection, Genetics and Evolution 11 (7), 1608-1615

  Article

  Cytokines are important players in the immune responses, and an unbalance in pro- and anti-inflammatory cytokine responses may affect parasitemia and pathology in a Plasmodium falciparum infection. Polymorphisms in cytokine genes may affect not only the levels of the protein, but many down-stream functions, such as production of C-reactive protein and immunoglobulin isotype switching. Susceptibility to malaria has been shown to differ between individuals with different genetic backgrounds, as indicated by studies in Fulani and non-Fulani ethnic groups. The aim of this study was to investigate possible interethnic differences in totally twelve single nucleotide polymorphisms (SNPs) in the genes encoding the cytokines IL-1β, IL-6, IL-10 and TNF. These SNPs are present in the promoter region of the genes, and have previously been associated with cytokine expression and with disease outcome in malaria. The results from the present study suggest that the Fulani ethnic group has a more pro-inflammatory response, due to high frequencies of high-producing alleles of IL1β and low-producing alleles of IL10. IL-6 could potentially also contribute to the relatively lower susceptibility to malaria in the Fulani ethnic group, whereas the TNF polymorphisms analysed in this study rather seem to associate with the severity of the infection and not the susceptibility for the infection itself. We therefore suggest that the polymorphisms analysed in this study all show a potential to influence the relatively lower susceptibility to malaria seen in the Fulani ethnic group as compared to the other sympatric ethnic groups.

  Read more about Cytokine gene haplotypes with a potential effect on susceptibility to malaria in sympatric ethnic groups in Mali

• Pattern of Pre-existing IgG Subclass Responses to a Panel of Asexual Stage Malaria Antigens Reported During the Lengthy Dry Season in Daraweesh, Sudan

  2011. A. Nasr (et al.). Scandinavian Journal of Immunology 74 (4), 390-396

  Article

  The anti-malarial IgG immune response during the lengthy and dry season in areas of low malaria transmission as in Eastern Sudan is largely unknown. In this study, ELISA was used for the measurement of pre-existing total IgG and IgG subclasses to a panel of malaria antigens, MSP2-3D7, MSP2-FC27, AMA-1 and Pf332-C231. The results showed that the antibody responses were predominantly age dependent, antigen specific, and their lifespan was at least 5-6 month long. Generally, the IgG3 was most abundant IgG subclass, and the most recognized antigen was Pf332-C231. Furthermore, the correlation between the levels of IgG subclasses was strongest between IgG1 and IgG3, which were more predictive to the total IgG levels. Finally, the response pattern of each of the IgG subclasses to the different test antigens that were spanning the dry season and the correlation between these responses were described in details for the first time.

  Read more about Pattern of Pre-existing IgG Subclass Responses to a Panel of Asexual Stage Malaria Antigens Reported During the Lengthy Dry Season in Daraweesh, Sudan

• Antibodies to the Plasmodiumfalciparum antigen Pf332 cooperated with human monocytes inhibit parasitegrowth by inducing intraerythrocytic abnormal parasite forms in vitro

  Lili Xu (et al.).

  IntraerythrocyticPlasmodium parasite proliferation istightly related to disease seriousness. Intraerythrocytic parasite developmentis fundamental to the proliferation of the malaria parasite which is affectedby many factors. Antibodies inhibiting intraerythrocytic parasite growth ordevelopment have been long indicated in protective immune mechanisms,particularly in cooperation with human monocytes. Here, we show that the developmentP. falciparum intraerythrocyticparasite was significantly disturbed by antibodies reactive with theintraerythrocytic parasitic antigen Pf332 by inducing parasites with anabnormal morphology. A synergistic effect in the induction of the abnormal formswas seen when antibodies cooperated with human monocytes. The long period of 48hours intraerythrocytic development provides a greater opportunity for antibodiesto react with the intraerythrocytic antigens than with merozoite stage antigens,which are exposed only for a short period of time.

  Read more about Antibodies to the Plasmodiumfalciparum antigen Pf332 cooperated with human monocytes inhibit parasitegrowth by inducing intraerythrocytic abnormal parasite forms in vitro

Show all publications by Klavs Berzins at Stockholm University