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- Ali, Magdi Mahmoud, 1963-
(author)
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Immunologic aspects of the pathogenesis of human onchocerciasis
- 2006
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Doctoral thesis (other academic/artistic)abstract
- Onchocerciasis, or river blindness, is a parasitic disease that affects more than 20 million people globally. The induction of pathology is directly related to the presence and destruction of the microfilarial stages (mf) of this filarial nematode. The disease presents clinically with a wide spectrum of dermal and ocular manifestations, the basis of the variation is believed to involve the immune system. The clinical presentations of infected hosts relate to the intensity of the reactions against the parasite. Anti-microfilarial drugs are also thought to somehow involve the immune system in their pharmacological action. In this study we have investigated some of the factors that might contribute to the pathogenesis, with the aim of gaining a better understanding of the role of immune response in these host inflammatory reactions to Onchocerca volvulus parasite. In the first study we have highlighted the clinically most severe form of dermal onchocerciasis, known as reactive onchocercal dermatitis (ROD), one that is often ignored and has not been properly identified. This form has special characteristics and important biological information that could greatly assist the general understanding of the disease as a whole. Amongst the three major foci of the disease in the study country, Sudan, the prevalence of ROD was found to be associated with different environmental and epidemiological characteristics; strikingly higher in the hypo-endemic areas. Including ROD cases in the prevalence will upgrade the level of endemicity of a locality, and often bring patients much in need of treatment into mass treatment programs that currently only treat localities with medium to high levels of endemicity. In the following research studies, we tried to address the immunological characteristics of the clinically different onchocerciasis patients. Then we also investigated the role of genetic polymorphism in the gene encoding receptor that links innate and adaptive immunity, namely, FcγRIIa.Patients with either of two major forms of the clinical spectrum-mild and severe dermatopathology were studied by assaying the antigen-driven proliferation of peripheral blood mononuclear cells and the ability of patients’ serum antibodies to promote cytoadherence activity to mf in vitro. Immune responses of those with severe skin disease were found to be stronger compared with the mild dermatopathology group. Mectizan® treatment was followed by an increase in immune responsiveness in those with initially poor responses. Thus the degree of dermatopathology is related to the host’s immune response against mf and immunocompetence may be necessary for Mectizan® to clear the infection efficiently.The infection has also been associated with increased levels of circulating immune complexes (CIC) containing parasite antigens and a cytokine response that involves both pro-and anti-inflammatory cytokines. Our fourth paper investigated the effect of IC from the O. volvulus infected patients on the production of pro-and anti-inflammatory cytokines. CIC were increased in all patients studied. The precipitate from plasma treated with polyethylene glycol (PEG) were added to peripheral blood mononuclear cell (PBMC) cultures, and the levels of IL-10, tumor necrosis factor TNF-α, IL-1β and their endogenous antagonists soluble TNF-Rp75 and IL-1-receptor antagonist (IL-1ra) were measured. A significant induction of all cytokines measured occurred in the onchocerciasis patients compared to healthy controls. However, the IL-1ra level was suppressed. The suppression of the production of IL-1ra suggests that the IC containing antigens may have a selectively suppressive effect on the production of this anti-inflammatory cytokine; thus implicating its possible role in counteracting inflammatory responses associated with the disease, and suggesting a potential therapeutic significance. FcgRIIa receptors are involved in many important biological responses, and considered as important mediators of inflammation. A polymorphism in the gene encoding this receptor, that is either arginine (R) or histidine (H) at position 131, affects the binding to the different IgG subclasses. We therefore hypothesized that this polymorphism might be one of the underlying mechanisms to the varied clinical presentations seen in this disease. FcgRIIa genotyping was carried out by gene specific polymerase chain reaction (PCR) and allele-specific restriction enzyme digestion of DNA from clinically characterized patients. The genotype R/R frequencies were found to be significantly higher among patients with the severe form of the disease (including ROD), and it was particularly associated with one tribe (Masaleet) compared to Fulani. Moreover, the H allele was found to be associated with lower risk of developing the severe form. As no significant difference was seen between onchocerciasis cases and controls, the study also implies that this polymorphism influences protection from developing the severe form rather than being related to protection from the infection.
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- Ali, Magdi M. M., et al.
(author)
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Fc gamma RIIa (CD32) polymorphism and onchocercal skin disease : implications for the development of severe reactive onchodermatitis (ROD)
- 2007
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In: American Journal of Tropical Medicine and Hygiene. - Lawrence, Kans. : American society of tropical medicine and hygiene. - 0002-9637 .- 1476-1645. ; 77:6, s. 1074-8
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Journal article (peer-reviewed)abstract
- The pathologic manifestations of Onchocerca volvulus infection depend on the interplay between the host and the parasite. A genetic single nucleotide polymorphism in the Fc gamma RIIa gene, resulting in arginine (R) or histidine (H) at position 131, affects the binding to the different IgG subclasses and may influence the clinical variations seen in onchocerciasis. This study investigated the relationship between this polymorphism and disease outcome. Fc gamma RIIa genotyping was performed on clinically characterized onchocerciasis patients (N = 100) and healthy controls (N = 74). Fc gamma RIIa genotype R/R131 frequencies were significantly higher among patients with severe dermatopathology (P < 0.001). Increased risk of developing this form was mostly associated with one tribe (Masalit) (OR = 3.2, 95% CI 1-9.9, P = 0.042). The H131 allele was found to be significantly associated with a reduced risk of having the severe form of the disease (adjusted OR = 0.26, 95% CI = 0.13-0.46, P < 0.001). Our findings suggest that the polymorphism influences the clinical outcome of onchocerciasis.
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- Awah, Nancy, 1976-, et al.
(author)
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Antibodies to the Plasmodium falciparum rhoptry protein RAP-2/RSP-2 in relation to anaemia in Cameroonian children
- 2011
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In: Parasite immunology (Print). - : Wiley. - 0141-9838 .- 1365-3024. ; 33:2, s. 104-115
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Journal article (peer-reviewed)abstract
- Previous studies have implicated reactive antibodies to the low molecular weight rhoptry-associated proteins (RAP-1, RAP-2/RSP-2 and RAP-3) in erythroid cell destruction during Plasmodium falciparum infection. In this pilot study, the frequency, specificity and functional capacity of naturally acquired anti-RAP-2/RSP-2 antibodies were investigated in the sera of anaemic and nonanaemic malaria-infected Cameroonian children. All sera recognized RAP-2/RSP-2 by FACS, irrespective of the clinical status of the subjects. However, the anaemic children showed higher levels of IgG antibodies than the nonanaemic group, while both groups showed similar levels of IgM antibodies. Only few individuals had detectable levels of RAP-2/RSP-2-specific IgG1 and IgG3 subclass antibodies, while no IgG2 and IgG4 subclass antibodies were detected in these subjects. By ELISA, the anaemic group tended to show higher levels of antibodies to RAP-2/RSP-2 regarding all antibody classes tested, except for IgG4 and IgE. Unexpectedly, sera from the nonanaemic group activated complement to a greater extent than those from the anaemic group. These results need to be confirmed in extended studies but indicate that the effector functions of the RAP-2/RSP-2-reactive antibodies may be more important than their amounts. Such antibodies could play a role in both immunity and pathogenesis during P. falciparum infection.
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- Awah, Nancy, 1976-
(author)
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Studies on Plasmodium falciparum asexual blood stage antigens : RAP-2/RSP-2 and Pf332 in focus
- 2011
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Doctoral thesis (other academic/artistic)abstract
- The life cycle of the malaria parasite is very complex and provides a number of potential targets for vaccination. In this thesis, data on two plasmodial asexual blood stage antigens (RAP-2 and Pf332) are presented. A partial aim of the work presented herein was to investigate the mechanisms responsible for the destruction of erythroid cells in anaemia, and more specifically to define the role of the rhoptry associated protein (RAP)-2 and other members of the RAP complex, RAP-1 and -3 in processes resulting in anaemia. Antibodies to the RAP complex were shown to have the potential to mediate the destruction of RAP-2-tagged erythroid cells by phagocytosis or by complement activation and lysis. In addition, antibodies to RAP-1 and RAP-2 could induce the apoptotic death of RAP-2- tagged erythroblasts. The frequency and functionality of naturally occurring RAP-2 antibodies in the sera of anaemic and non-anaemic Cameroonian children were also investigated. All sera tested contained RAP-2-reactive antibodies by both immunofluorescence and flow cytometry. The anaemic group of children had higher levels of IgG than the non-anaemic ones, while the levels of IgM were similar. With respect to IgG subclasses, higher levels of IgG3 were seen in the non-anaemic individuals as compared to anaemic subjects. The non-anaemic individuals recognised a greater proportion of RAP-2-tagged RBCs and activated complement to a greater extent than the anaemic ones. Earlier studies observed that humans continuously exposed to malaria, recognised Pf332 extensively. Further studies revealed that Pf332 antibodies were able to inhibit parasite growth and cytoadherence in vitro. Making use of Pf332-C231, a sub-fragment of Pf332, we studied the effects/mode of action of C231-specific antibodies on P. falciparum parasite growth and development in vitro. The antibodies appeared to act mainly on late stage parasites by two main mechanisms: 1) through the induction of abnormal/pyknotic parasites, and, 2) RBC lysis (disintegration of RBCs), thus limiting parasite growth and development. The antibody isotype in this context was IgG. Following the removal of immune pressure, parasites resumed growth, albeit at a much slower rate. The results suggest that during natural infections, antibodies to C231 could play a role in parasite control. In summary, these data suggest that antibodies to both antigens could be instrumental in immune responses leading to disease control, but could also mediate pathology.
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- Awah, Nancy W., et al.
(author)
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Mechanisms of malarial anaemia : potential involvement of the Plasmodium falciparum low molecular weight rhoptry-associated proteins.
- 2009
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In: Acta Tropica. - : Elsevier BV. - 0001-706X .- 1873-6254. ; 112:3, s. 295-302
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Journal article (peer-reviewed)abstract
- Plasmodium falciparum malaria is a major cause of morbidity and mortality throughout the tropics. Anaemia is a constant feature of the disease. Pregnant women mostly primigravidae and children below the age of 5 years are the most afflicted. Its pathogenesis is multifactorial and incompletely understood. Among several factors, the destruction of erythrocytes (RBCs) is the most frequently observed cause of severe malarial anaemia and the removal of non-parasitized RBCs (nEs) is thought to be the most important, accounting for approximately 90% of the reduction in haematocrit in acute malaria. Previous studies demonstrated that the tagging of nEs with the parasite antigen RAP-2 (rhoptry-associated protein-2; also designated RSP-2) due to either failed or aborted invasion by merozoites resulted in the destruction of these cells. In this study we further investigated the mechanisms mediating the destruction of nEs in the development of severe malarial anaemia and the possible involvement of RAP-2/RSP-2 and other members of the low molecular weight rhoptry complex (RAP-1: rhoptry-associated protein-1 and RAP-3: rhoptry-associated protein-3). Antibodies to the rhoptry-associated proteins were found to recognise the surface of nEs in a parasitaemia-dependent manner after merozoite release in P. falciparumin vitro cultures. These cells, as well as erythroblasts co-cultured with infected RBCs (IEs), could then be destroyed by either phagocytosis or lysis after complement activation. The ability of anti-rhoptry antibodies to mediate the destruction of RAP-2/RSP-2-tagged erythroblasts in the presence of effector cells was also investigated. Data obtained suggest that mouse monoclonal antibodies to the low molecular weight RAP proteins mediate the death of RAP-2/RSP-2-tagged erythroblasts on interaction with adherent monocytes. The mechanism of cell death is not yet fully known, but seems to involve primarily apoptosis. The above observations suggest that the antibody response against RAP-2/RSP-2 and other members of the complex could trigger the destruction of RAP-2/RSP-2-tagged host cells. Taken together it appears that during severe anaemia a defective bone marrow or dyserythropoiesis possibly due to erythroblast cell death, may overlap with the accelerated destruction of normal erythroid cells, either by opsonisation or complement activation further aggravating the anaemia which may become fatal. These observations could therefore have implications in the design, development and deployment of future therapeutic interventions against malaria.
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- Balogun, Halima A., et al.
(author)
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Immunogenicity and antigenic properties of Pf332-C231, a fragment of a non-repeat region of the Plasmodium falciparum antigen Pf332
- 2009
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In: Vaccine. - : Elsevier BV. - 0264-410X .- 1873-2518. ; 28:1, s. 90-97
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Journal article (peer-reviewed)abstract
- Antigen Pf332, a megadalton protein has been shown to be associated with the membrane of infected erythrocytes. Detailed functional studies on the antigen have remained hampered by the cross-reactive nature of antibodies generated to Pf332. Pf332-C231, identified in the C-terminal region of Pf332 was cloned and antibodies against the C231 fragment were shown to react with intact Pf332 antigen by both immunofluorescence and immunoblotting analyses. Antibodies to C231 inhibited in vitro Plasmodium falciparum growth efficiently. In addition, human sera from malaria-exposed individuals reacted with recombinant C231. We show that Pf332-C231 represents a functional domain and is expected to facilitate further studies on Pf332 as a potential target for protective immune responses and the function of the antigen.
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- Balogun, Halima Aramide, 1978-
(author)
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Immunological characteristics of a C-terminal fragment of the Plasmodium falciparum blood-stage antigen Pf332
- 2006
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Licentiate thesis (other academic/artistic)abstract
- Till date, there are no effective control strategies against the deadly disease of malaria, and millions of children across Africa, Oceania, Asia, and Latin America are at the mercy of this long term enemy of man every second that passes by. Other control measures combined with vaccination might help improve control strategy against malaria, but the development of vaccines face various challenges as well, due to the complexity of the parasites’ life cycle and other host factors. The asexual blood stage antigen Pf332 of Plasmodium falciparum, is expressed during the trophozoite stage, and transported from the parasitophorous membrane to the outer erythrocyte membrane during schizogony. Previous studies have suggested this antigen as a potential vaccine candidate, because Pf332-reactive human monoclonal antibody (mAb 33G2) inhibits parasite growth and cytoadherence in vitro. Elucidating and understanding the immunological capabilities of antigen Pf332, as a vaccine candidate was the aim of the studies presented in this thesis. In our first study we identified and characterized the immunogenicity of a non-repeat fragment of antigen Pf332, termed Pf332-C231, a 231 amino acids long fragment corresponding to 13 percent of the total protein. Various analyses carried out with this fragment reveal that recombinant C231 was immunogenic in rabbits. In addition, anti- C231 antibodies have in vitro inhibitory capabilities. In immunoflourescence and immunoblot assays, rabbit anti-C231 antibodies were able to recognize the native protein. In the other study, we examined the distribution of antibodies regarding recombinant C231 and crude P. falciparum extract in a malaria endemic area of Senegal. IgG antibody reactivity with crude P. falciparum antigen was detected in the sera of all the donors while many of the children lacked or had low levels of such antibodies against C231. The distribution of the anti-C231 antibodies in the different IgG subclasses differed from that shown by crude P. falciparum antigen. The crude P. falciparum antigen gives a higher IgG3 response than IgG2 for all age-groups, while C231 gave similar levels of IgG2 and IgG3. Correlation studies showed that the levels of anti-C231antibodies were associated with protection from clinical malaria, but this only reached significance with IgE. These findings further emphasize the inclusion of antigen Pf332 as a subunit vaccine candidate against P. falciparum malaria.
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