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Title: The role of immunoglobulin M in immune evasion by Plasmodium falciparum
Author: Lloyd, Katy
ISNI:       0000 0004 5357 0592
Awarding Body: University of Liverpool
Current Institution: University of Liverpool
Date of Award: 2015
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Plasmodium falciparum parasites have evolved numerous ingenious methods to subvert immune recognition, in order to survive within the human host. One such immune evasion mechanism features the expression of ligands which bind to the Fcportion of human IgM. The binding of IgM to P. falciparum-encoded PfEMP1 molecules expressed on infected erythrocyte surfaces has been well characterised. Recently, two novel IgM-binding proteins expressed on merozoites were identified, known as DBLMSP and DBLMSP2. The aim of this project was to characterise the binding of these merozoite surface proteins to IgM, and to investigate what advantage IgM binding may afford P. falciparum merozoites. Although DBLMSP and DBLMSP2 have been implicated in camouflaging critical epitopes from immune responses, it is unknown whether these proteins function to alter the binding of IgM to IgM-receptors, such as the human Fcµ receptor. A panel of domain-swap antibodies, in which homologous domains are exchanged between human IgA and IgM, identified the Cµ4 domain of human IgM as the target of both the DBLMSP proteins and hFcµR. Despite this, the binding of DBLMSP and DBLMSP2 to IgM did not prevent its binding to hFcµR, suggesting the malarial proteins recognise an alternative region on IgM than that recognised by hFcµR. In fact, DBLMSP and DBLMSP2 engaged IgM bound to both hFcµR and DC-SIGN, which was found to facilitate interactions of these malarial proteins with IgMpositive human lymphocytes. However, binding of recombinant DBLMSP and DBLMSP2 per se did not induce proliferation or apoptosis of human lymphocytes. A possible explanation for this is that DBLMSP and DBLMSP2 were found to exist in complex with IgM and other unidentified parasite molecules. This suggests that these proteins associate with other merozoite surface proteins in vivo, which could potentially induce functional consequences upon lymphocyte binding. This thesis lays the foundation for future research into how native IgM-parasite protein complexes may function to bind to lymphocytes and modulate host immune responses. This thesis also presents data that hFcµR functions as an endocytosis receptor for human IgM, in which the binding and internalisation of human IgM occurs in a glycan-independent manner.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
Keywords: Q Science (General) ; QR180 Immunology