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CD4+ T cell responses to the Plasmodium falciparum erythrocyte membrane protein 1 in children with mild malaria.

ABSTRACT: The immune response against the variant surface Ag Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is a key component of clinical immunity against malaria. We have investigated the development and maintenance of CD4(+) T cell responses to a small semiconserved area of the Duffy binding-like domain (DBL)?-domain of PfEMP1, the DBL?-tag. Young children were followed up longitudinally, and parasites and PBMCs were isolated from 35 patients presenting with an acute case of uncomplicated malaria. The DBL?-tag from the PfEMP1 dominantly expressed by the homologous parasite isolate was cloned and expressed as recombinant protein. The recombinant DBL?-tag was used to activate PBMCs collected from each acute episode and from an annual cross-sectional survey performed after the acute malaria episode. In this article, we report that CD4(+) T cell responses to the homologous DBL?-tag were induced in 75% of the children at the time of the acute episode and in 62% of the children at the following cross-sectional survey on average 235 d later. Furthermore, children who had induced DBL?-tag-specific CD4(+)IL-4(+) T cells at the acute episode remained episode free for longer than children who induced other types of CD4(+) T cell responses. These results suggest that a wide range of DBL?-tag-specific CD4(+) T cell responses were induced in children with mild malaria and, in the case of CD4(+)IL-4(+) T cell responses, were associated with protection from clinical episodes.

SUBMITTER: Gitau EN

PROVIDER: S-EPMC3918862 | biostudies-literature | 2014 Feb

REPOSITORIES: biostudies-literature

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CD4+ T cell responses to the Plasmodium falciparum erythrocyte membrane protein 1 in children with mild malaria.

Gitau Evelyn N EN Tuju James J Karanja Henry H Stevenson Liz L Requena Pilar P Kimani Eva E Olotu Ally A Kimani Domtila D Marsh Kevin K Bull Peter P Urban Britta C BC

Journal of immunology (Baltimore, Md. : 1950) 20140122 4

The immune response against the variant surface Ag Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1) is a key component of clinical immunity against malaria. We have investigated the development and maintenance of CD4(+) T cell responses to a small semiconserved area of the Duffy binding-like domain (DBL)α-domain of PfEMP1, the DBLα-tag. Young children were followed up longitudinally, and parasites and PBMCs were isolated from 35 patients presenting with an acute case of uncomplicate ...[more]

PMID: 24453249

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Project description:Plasmodium falciparum malaria remains one of the most deadly infections worldwide. The pathogenesis of the infection results from the sequestration of infected erythrocytes (IRBC) in vital organs, including the brain, with resulting impairment of blood flow, hypoxia, and lactic acidosis. Sequestration occurs through the adhesion of IRBC to host receptors on microvascular endothelium by Plasmodium falciparum erythrocyte membrane protein 1 (PfEMP1), a large family of variant surface antigens, each with up to seven extracellular domains that can bind to multiple host receptors. Consequently, antiadhesive therapies directed at single endothelial adhesion molecules may not be effective. In this study, we demonstrated that the serine protease thrombin, which is pivotal in the activation of the coagulation cascade, cleaved the major parasite adhesin on the surface of IRBC. As a result, adhesion under flow was dramatically reduced, and already adherent IRBC were detached. Thrombin cleavage sites were mapped to the Duffy binding-like δ1 (DBLδ1) domain and interdomains 1 and 2 in the PfEMP1 of the parasite line IT4var19. Furthermore, we observed an inverse correlation between the presence of thrombin and IRBC in cerebral malaria autopsies of children. We investigated a modified (R67A) thrombin and thrombin inhibitor, hirugen, both of which inhibit the binding of substrates to exosite I, thereby reducing its proinflammatory properties. Both approaches reduced the barrier dysfunction induced by thrombin without affecting its proteolytic activity on PfEMP1, raising the possibility that thrombin cleavage of variant PfEMP1 may be exploited as a broadly inhibitory antiadhesive therapy. Plasmodium falciparum malaria is the third leading cause of mortality due to a pathogen, with 214 million people infected and 438,000 deaths annually. The adhesion of Plasmodium falciparum-infected erythrocytes (IRBC) to microvascular endothelium is a major pathological process in severe malaria. While the recent implementation of artemisinin-based antimalarial therapy for severe malaria improves patient survival by targeting all parasite stages, antiparasite drugs alone may not immediately reverse pathophysiological processes in occluded vessels. Here we show that thrombin, an enzyme intimately involved in the clotting process, cleaves the main parasite adhesin expressed on the surface of IRBC, thereby preventing and reversing the binding of IRBC to endothelial cells. This beneficial effect of thrombin can be achieved by modified thrombins that cause significantly less clotting and vessel leakage while preserving the ability to cleave the parasite protein. Our results provide the basis for using modified thrombins as adjunctive therapy in severe malaria.

Dataset Information

CD4+ T cell responses to the Plasmodium falciparum erythrocyte membrane protein 1 in children with mild malaria.

Publications

CD4+ T cell responses to the Plasmodium falciparum erythrocyte membrane protein 1 in children with mild malaria.

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