Evaluation of immunogenicity and protective efficacy of carrier-free Plasmodium falciparum R23 antigen in pre-exposed saimiri sciureus monkeys

[IgG responses to candidate malaria vaccine antigens in the urban area of Dakar (Senegal): evolution according to age and parasitemia in patients with mild symptoms]

Malaria remains a major problem in African countries despite substantial decreases in morbidity and mortality due to sustained control programs. Studies for the evaluation of qualitative or quantitative Ab responses to key targets of anti-plasmodium immunity were mostly done in rural endemic setting compared to urban area. In a cohort of 200 patients with mild malaria and living in Dakar, we analyze total and subclasses IgG responses to a panel of P. falciparum blood stage antigens: MSP1p19, MSP3, EB200, GST-5 and R23. A mean age of 15 yrs (4 to 56 yrs) and parasitemia between 0.1 to 17% were found. Levels of IgG anti-MSP3 were higher in patients with low parasitemia (≤1%) and appear negatively correlated to parasite densities (Rho =. 0.54; p= 0.021). This correlation is more significant in children (≤ 15 yrs). In addition, an increase of IgG responses against MSP1p19 is highly observed in adults having a parasitemia less than 1%. In those patients, we find that IgG1 subclasses were predominant (p <0.01). Our study shows an association between Ab responses and parasitemia. This association is dependant to IgG anti-MSP3 in children and IgG anti-MSP1p19 in adults living in urban area.

Association of antibody responses to the conserved Plasmodium falciparum merozoite surface protein 5 with protection against clinical malaria

Background

Plasmodium falciparum merozoite surface protein 5 (PfMSP5) is an attractive blood stage vaccine candidate because it is both exposed to the immune system and well conserved. To evaluate its interest, we investigated the association of anti-PfMSP5 IgG levels, in the context of responses to two other conserved Ags PfMSP1p19 and R23, with protection from clinical episodes of malaria in cross-sectional prospective studies in two different transmission settings.

Methods

Ndiop (mesoendemic) and Dielmo (holoendemic) are two Senegalese villages participating in an on-going long-term observational study of natural immunity to malaria. Blood samples were taken before the transmission season (Ndiop) or before peak transmission (Dielmo) and active clinical surveillance was carried out during the ensuing 5.5-month follow-up. IgG responses to recombinant PfMSP5, PfMSP1p19 and R23 were quantified by ELISA in samples from surveys carried out in Dielmo (186 subjects) and Ndiop (221 subjects) in 2002, and Ndiop in 2000 (204 subjects). In addition, 236 sera from the Dielmo and Ndiop-2002 surveys were analyzed for relationships between the magnitude of anti-PfMSP5 response and neutrophil antibody dependent respiratory burst (ADRB) activity.

Results

Anti-PfMSP5 antibodies predominantly IgG1 were detected in 60–74% of villagers, with generally higher levels in older age groups. PfMSP5 IgG responses were relatively stable for Ndiop subjects sampled both in 2000 and 2002. ADRB activity correlated with age and anti-PfMSP5 IgG levels. Importantly, PfMSP5 antibody levels were significantly associated with reduced incidence of clinical malaria in all three cohorts. Inclusion of IgG to PfMSP1p19 in the poisson regression model did not substantially modify results.

Conclusion

These results indicate that MSP5 is recognized by naturally acquired Ab. The large seroprevalence and association with protection against clinical malaria in two settings with differing transmission conditions and stability over time demonstrated in Ndiop argue for further evaluation of baculovirus PfMSP5 as a vaccine candidate.

Serotype distribution and antimicrobial susceptibility of Streptococcus pneumoniae strains isolated from middle ear fluids of children aged 0–24 months with acute otitis media

Az akut otitis media a két éven aluli korcsoport egyik leggyakoribb betegsége, amelynek legfőbb bakteriális kórokozója a Streptococcus pneumoniae . A jelenleg elérhető, hét szerotípus elleni védelmet adó konjugált pneumococcusvakcina világszerte jelentős hatással van az otitis media, különösen a vakcinában megtalálható hét szerotípusba tartozó pneumococcusok okozta otitis media előfordulására. Az oltás hatékonysága az adott régióban észlelt otopatogén pneumococcus törzsek szerotípus-megoszlásától függ. A vizsgálat célja: Kétévesnél fiatalabb gyermekekben középfülgyulladást okozó S. pneumoniae törzsek szerotípusának és antibiotikum-érzékenységének meghatározása, és ezek összehasonlítása a nemzetközi adatokkal. Betegek és módszerek: 2002 és 2005 között 10 budapesti gyermekgyógyászati intézményben megjelent, 0–24 hónapos korú, otitis media acutában szenvedő gyermek dobüregi váladékából 73 S. pneumoniae törzset izoláltunk, amelyeket a Fővárosi Szent László Kórház Mikrobiológiai Laboratóriumában identifikáltuk és Quellung-reakció segítségével szerotipizáltuk. Az antibiotikum-érzékenységi vizsgálatokat a laboratórium a Magyar Mikrobiológiai Társaság által elfogadott standard módszerek alapján végezte és értékelte. Eredmények: A 73 izolált S. pneumoniae törzs 14 szerotípust reprezentált. A 14 (13,7%), a 19F (13,7%), a 6B (13,7%), a 23A (11%) és a 3 (9,6%) szerotípusok voltak a leggyakoribbak. A törzsek 63%-a tartozott a hét szerotípus ellen védelmet nyújtó konjugált vakcinában megtalálható szerotípusba. A penicillinre mérsékelten érzékeny törzsek aránya 41% volt, e törzsek 90%-a a vakcina szerotípusaiba tartozott. Penicillinrezisztenciát nem észleltünk. A leginkább rezisztens törzsek a 9V, 14, 19F szerotípusokba tartoztak. Következtetés: Az otopatogén S. pneumoniae törzsek szerotípus-megoszlása a hét szerotípus ellen védelmet adó konjugált pneumococcusvakcináció szempontjából az egyéb régiókban megismerteknek megfelel. Ennek alapján az oltás hatása az otitis media előfordulására a külföldi tanulmányokban igazoltakhoz hasonló lehet majd Magyarországon is.

Blood typing in Saimiri sciureus monkeys: influence of anti-red blood cell alloantibodies on Plasmodium falciparum parasitaemia in vivo

The Saimiri sciureus monkey is a well-established host for experimental studies with human malaria parasites. During the course of iterative inoculations with Plasmodium falciparum parasitised red blood cells (RBC), anti-RBC alloantibodies were detected in the sera of two of eight Saimiri monkeys. These anti-RBC antibodies were further used to investigate RBC phenotypes in 35 colony-reared Saimiri monkeys by flow cytometry. Three RBC phenotypes (named I-III) were observed. Their distribution was I (86%), II (11%) and III (3%). Using the Palo Alto FUP-2 strain, a variant P. falciparum line insensitive to hyperimmune serum and the passive transfer of anti-RBC alloantibodies, a dramatic drop in parasite growth was documented in an incompatible monkey.

A new Apicomplexa-specific protein kinase family: multiple members in Plasmodium falciparum, all with an export signature

Background

Malaria caused by protozoan parasites of the genus Plasmodium spp. is a major health burden in tropical countries. The development of new control tools, including vaccines and drugs, is urgently needed. The availability of genome sequences from several malaria parasite species provides a basis on which to identify new potential intervention targets. Database mining for orthologs to the Plasmodium falciparum trophozoite protein R45, a vaccine candidate, led us identify a new gene family.

Results

Orthologs to the P. falciparum trophozoite protein R45 were detected exclusively in protozoan parasites of the phylum Apicomplexa, including several Plasmodium spp., Toxoplasma gondii and Cryptosporidium parvum. All family members are hybrid genes with a conserved C-terminal protein kinase domain of a novel type, recently called FIKK kinase, associated with a non conserved N-terminal region without any known functional signature. While a single copy gene was detected in most species, considerable gene expansion was observed in P. falciparum and its closest phylogenic relative P. reichenowi, with 20 and six copies, respectively, each with a distinct N-terminal domain. Based on full length protein sequence, pairs of orthologs were observed in closely related species, such as P. berghei and P.y. yoelii, P. vivax and P. knowlesi, or P. reichenowi and P. falciparum. All 20 P. falciparum paralogs possess a canonical Plasmodium export element downstream of a signal / anchor sequence required for exportation outside the parasitophorous vacuole. This is consistent with the reported association of the trophozoite protein R45, the only paralog characterised to date, with the infected red blood cell membrane. Interestingly, most genes are located in the subtelomeric region of chromosomes, in association with other multigene families contributing to the remodelling of the infected red blood cell membrane, in particular the ring erythrocyte surface antigen multigene family.

Conclusion

This Apicomplexan-specific gene family was called R45-FIKK kinase. The family hallmark is a kinase domain with unusual characteristics, raising the possibility of designing drug or vaccine strategies targeting this domain. The characteristics of the P. falciparum family suggest a role in remodelling the infected cell and as such possibly contribute to the particular virulence of this species.

Flow cytometry identification and characterization of mononuclear cell subsets in the neotropical primate Saimiri sciureus (squirrel monkey)

BACKGROUND

The neotropical primate squirrel monkey is used in many areas of biomedical research including neuroendocrinology, immunology and infectious diseases. However, research has been hampered by the lack of immunological tools for this primate.

METHODS

A series of 67 commercially available monoclonal antibodies to human CD antigens or cytokines were tested on Saimiri mononuclear cells and the specificity was assessed by double staining using flow cytometry.

RESULTS

Monoclonal antibodies defining the main mononuclear cells subsets (monocytes, B, T, including CD4 and CD8 T cells) as well as activation markers have been identified. The conditions to specifically identify the various cell subsets using two color flow cytometry and establish their relative proportions have been set-up. We also have established normal values of the main circulating mononuclear cell subsets for adult Saimiri sciureus monkeys from the breeding unit of Institut Pasteur in French Guiana. The distribution between spleen, blood and lymph nodes has been compared.

CONCLUSIONS

These tools allow documenting the phenotype of most Saimiri mononuclear cell subsets and assessing their activation level. This opens new perspectives for vaccinology and immunopathology research in this experimental non-human primate host, in particular for malaria research.

Relationship of binding of immunoglobulin G to Plasmodium falciparum-infected erythrocytes with parasite endemicity and antibody responses to conserved antigen in immune individuals

To investigate the potential for use of a well-established strain of Plasmodium falciparum as a reference strain for infected red blood cell (IRBC) surface reactivity, we monitored the binding of specific immunoglobulin G (IgG) from immune individuals to the reference Knob-positive FCR3 strain by flow cytometry. To permit interassay comparison for 162 plasma samples drawn after the rainy season, a labeling index (LI) was defined as the percentage of labeled parasites multiplied by the mean peak intensity. An LI ratio (LIR) was then calculated as the LI of the sample divided by the LI of the control. LIRs were calculated for individuals living in Dielmo and Ndiop, two Senegalese villages where P. falciparum is transmitted holoendemically and mesoendemically, respectively. The incidence (persons with an LIR of >3) observed in Dielmo was lower than that observed in Ndiop. Significantly higher LIRs were observed (i) for samples from Ndiop than for samples from Dielmo (P < 0.01) and (ii) in Ndiop, in subjects with hemoglobin AS (HbAS) than in those with hemoglobin AA (P = 0.03). No correlation with the cumulative age-associated immune status of the villagers was evidenced, contrary to antibody (Ab) responses against conserved IRBC-associated antigen (Ag) measured by enzyme-linked immunosorbent assay. These results are consistent with the notions that protection in HbAS individuals may relate to an increased IgG response to IRBC membrane Ags and that cell surface reactivity parallels IgG responses even though it is in itself a distinct indicator of the anti-P. falciparum Ab response. Measures of IgG binding to live IRBC are thus relevant for the functional screening of conserved IRBC-associated Ags that contribute to parasite destruction in vivo, as these Ags might be included in a multitarget vaccine.