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- Ahmed Ismail, Hodan
(författare)
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Functional antibody responses to the Plasmodium falciparum merozoite
- 2014
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Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
- Plasmodium falciparum is a leading cause of death among children under the age of five and pregnant women in sub-Saharan Africa. More than one third of the world’s population is at risk of contracting malaria, and 70 % of the cases are found in sub-Saharan Africa. Emerging drug resistance in parasites and limited effect of vector control calls for an effective vaccine. It is known that individuals living in malaria endemic countries develop naturally acquired immunity after repeated exposure. Antibodies are important components of acquired immunity, and it has been shown that passive transfer of antibodies from immune donors to individuals with P. falciparum infections reduced parasitemia and clinical symptoms. Antibodies against several P. falciparum merozoite antigens have been found to be associated with protective immunity. It is of great importance to understand the underlying functional role of antibodies in the development of protective immunity against severe malaria. In a cross-sectional study in Uganda, the quantitative and qualitative differences in antibody responses to a panel of merozoite antigens in children with uncomplicated or severe malaria were evaluated using a set of assays including ELISA, Invasion Inhibition Assays (IIA), NH4SCN-ELISA and Surface Plasmon Resonance (SPR). Children with uncomplicated malaria had higher antibody levels against PfEBA-181, MSP2-Fc27, MSP2-3D7 and PfAMA1 when compared to children with severe malaria. Acquired antibodies against PfRh2 and PfAMA1 in ELISA correlated with invasion inhibition of two clinical isolates in IIA, and anti-PfAMA1-antibodies in ELISA correlated with increased anti- PfAMA1-antibody affinity in SPR. Importantly, the only assay that correlated with initial parasitemia in the children was the IIA. Both MSP2-Fc27 and MSP2-3D7 allelic variants were present in both children groups, but there was a higher number of genotypes in uncomplicated malaria compared to in children with severe malaria. P. falciparum clinical isolates collected from Ugandan children with uncomplicated malaria or severe malaria were further investigated for rosetting, parasite multiplication and RBC invasion. Optimal in vitro growth conditions were established, which allowed for phenotypic studies of clinical P. falciparum isolates. Presence of serum in growth cultures was found to be essential for optimal surface presentation of PfEMP1 and maintenance of rosettes. Higher peripheral parasitemia, higher rosetting levels and higher multiplication rates were observed in children with severe malaria and these correlated positively with one another. Rosetting might enhance successful merozoite invasion in vivo, hence could be the reason it is found to be associated with severe disease. Furthermore, parasite invasion into trypsinand chymotrypsin-treated RBC differed between the uncomplicated and severe groups, and isolates from children with uncomplicated malaria showed higher sensitivity to enzyme treatment. The majority of clinical isolates used a sialic acid independent invasion pathway. Parasite invasion is central to parasite replication and virulence, and it is essential to know which invasion pathways are used for vaccine studies. Naturally acquired antibody responses to P. falciparum merozoite antigens was further studied in a longitudinal study over almost one year in children and adults from Nigeria. The malaria protective effects of the hemoglobin S (HbAS) allele were also investigated. In both children and adults, the antibody response against PfEBA175 was more prominent than that against PfRh2, and cytophilic IgG1 and IgG3 against PfEBA175 were the predominant antibodies even though we could also see some response for IgG2 and IgG4. Individuals with higher total IgG responses against both PfEBA175 and PfRh2 had lower parasitemia over the course of the study period. Furthermore, children with HbAS had higher antibody responses against merozoite antigens compared to adults, and this might have protective effects against malaria. In conclusion this thesis emphasizes the great importance of using a combination of functional assays, such as SPR and IIA, to study the functional role of acquired antibodies in the development of protective immunological responses against severe malaria. Furthermore, investigations of parasite invasion and rosetting in the context of pathogenesis of severe malaria are crucial as both are important for parasite replication and virulence. Taken together, future vaccine studies should include functional assays that would allow the investigation of differences in immunological responses against severe and uncomplicated malaria. Also, to consider the protective effects of red blood polymorphisms and their role in acquired immunity in the populations, would be of great value for future vaccine studies.
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| 2. |
- Eeg-Olofsson, Katarina, 1968, et al.
(författare)
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Real-world study of flash glucose monitoring among adults with type 2 diabetes within the Swedish National Diabetes Register
- 2022
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Ingår i: DIABETES & VASCULAR DISEASE RESEARCH. - : SAGE Publications. - 1479-1641 .- 1752-8984. ; 20:1
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Tidskriftsartikel (refereegranskat)abstract
- BackgroundThe Swedish National Diabetes Register (NDR) initiated registration of the FreeStyle Libre (R) system and other continuous glucose monitoring (CGM) systems in June 2016. We investigated change in HbA1c for people with type 2 diabetes (T2DM) using FreeStyle Libre in Sweden.MethodsWe included adults with T2DM, registered in the NDR after January 1, 2014, and an index date for first use of FreeStyle Libre of June 2016 or later. Methodology was a before/after comparison of HbA1c within 6 months before the index date versus HbA1c around 6 and 12 months after the index date.Results711 adults with T2DM using FreeStyle Libre had HbA1c measurements within the study period. Mean HbA1c was significantly reduced at 6 months (-0.50%-unit) and at 12 months (-0.52%-unit) in this group. Degree of change was negatively correlated to baseline HbA1c. Reductions in HbA1c were observed in incident users of FreeStyle Libre with T2DM who were truly naive to CGM or had unknown prior experience of CGM, and aged 25-74 years.ConclusionsThis real-world study on the Swedish NDR shows that people with T2DM using FreeStyle Libre system for 6 and 12 months significantly reduced their HbA1c.
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| 3. |
- Ismail, Hodan Ahmed, et al.
(författare)
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Subclass responses and their half-lives for antibodies against EBA175 and PfRh2 in naturally acquired immunity against Plasmodium falciparum malaria
- 2014
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Ingår i: Malaria Journal. - : Springer Science and Business Media LLC. - 1475-2875. ; 13
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Tidskriftsartikel (refereegranskat)abstract
- Background: Plasmodium falciparum EBA175 and PfRh2 belong to two main families involved in parasite invasion, and both are potential vaccine candidates. Current knowledge is limited regarding which target antigens and subclasses of antibodies are actually important for protection, and how naturally acquired immunity is achieved. Methods: Repeated blood samples were collected from individuals in Nigeria over a period of almost one year. ELISA was used to analyse subclasses of IgG responses. Results: For both EBA175 (region III-V) and (a fragment of) PfRh2, the dominant antibody responses consisted of IgG1 and IgG3 followed by IgG2, while for PfRh2 there was also a relatively prominent response for IgG4. High levels of IgG1, IgG2 and IgG3 for EBA175 and total IgG for PfRh2 correlated significantly with a lower parasitaemia during the study period. Children with HbAS had higher levels of some subclasses compared to children with HbAA, while in adults the pattern was the opposite. The half-lives of IgG2 and IgG4 against EBA175 were clearly shorter than those for IgG1 and IgG3. Conclusion: EBA175 and PfRh2 are potential targets for protective antibodies since both correlated with lower parasitaemia. The shorter half-lives for IgG2 and IgG4 might explain why these subclasses are often considered less important in protection against malaria. Triggering the right subclass responses could be of critical importance in a successful vaccine. Further studies are needed to evaluate the role of haemoglobin polymorphisms and their malaria protective effects in this process.
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| 4. |
- Ribacke, Ulf, et al.
(författare)
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Improved in vitro culture of plasmodium falciparum permits establishment of clinical isolates with preserved multiplication, invasion and rosetting phenotypes
- 2013
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Ingår i: PLOS ONE. - : Public Library of Science. - 1932-6203. ; 8:7
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Tidskriftsartikel (refereegranskat)abstract
- To be able to robustly propagate P. falciparum at optimal conditions in vitro is of fundamental importance for genotypic and phenotypic studies of both established and fresh clinical isolates. Cryo-preserved P. falciparum isolates from Ugandan children with severe or uncomplicated malaria were investigated for parasite phenotypes under different in vitro growth conditions or studied directly from the peripheral blood. The parasite cultures showed a minimal loss of parasite-mass and preserved percentage of multiple infected pRBCs to that in peripheral blood, maintained adhesive phenotypes and good outgrowth and multiplication rates when grown in suspension and supplemented with gas. In contrast, abnormal and greatly fluctuating levels of multiple infections were observed during static growth conditions and outgrowth and multiplication rates were inferior. Serum, as compared to Albumax, was found necessary for optimal presentation of PfEMP1 at the pRBC surface and/or for binding of serum proteins (immunoglobulins). Optimal in vitro growth conditions of P. falciparum therefore include orbital shaking (50 rev/min), human serum (10%) and a fixed gas composition (5% O2, 5% CO2, 90% N2). We subsequently established 100% of 76 frozen patient isolates and found rosetting with schizont pRBCs in every isolate (>26% schizont rosetting rate). Rosetting during schizogony was often followed by invasion of the bound RBC as seen by regular and time-lapse microscopy as well as transmission electron microscopy. The peripheral parasitemia, the level of rosetting and the rate of multiplication correlated positively to one another for individual isolates. Rosetting was also more frequent with trophozoite and schizont pRBCs of children with severe versus uncomplicated malaria (p<0.002; p<0.004). The associations suggest that rosetting enhances the ability of the parasite to multiply within the human host.
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