Structural and functional studies of mannose binding lectin (MBL) and the lectin pathway of complement in children with cancer

• Main Author: Dommett, Rachel Mary
• Published: University College London (University of London) 2008
• Subjects: 618.92
• Online Access: http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.502649

Infection remains a major cause of morbidity and hospitalisation in children receiving chemotherapy treatment for cancer. Among patients with the same diagnosis and treatment regimen, not all suffer equally from infectious complications. This suggests that as yet unidentified host factors may contribute to increased susceptibility to infection. Deficiency of mannose binding lectin (MBL), a pattern recognition receptor of the innate immune system, has been proposed as one such factor but clinical studies have been inconclusive. MBL works in concert with MBL associated serine proteases (MASPs) to activate the lectin pathway of complement. Functional activity of the pathway has not been investigated in children with cancer to date. Children undergoing chemotherapy were recruited to cross sectional observational and longitudinal studies with details of febrile neutropenia (FN) episodes recorded prospectively. MBL gene polymorphisms were characterized by heteroduplexing and reverse hybridization. MBL protein and MASP levels were measured and functional activity of the lectin pathway was quantified. High oligomer structure of MBL was analysed by Western blotting. Transcriptional regulation of MBL in response to infection and inflammation was studied. The MBL promoter was cloned and its activity investigated using luciferase assays. A major finding is that individuals in possession of MBL variant alleles suffered from more frequent and longer episodes of FN over the study period compared to wildtype individuals. Functional analysis enabled identification of specific deficiencies within the pathway in patients deemed MBL sufficient by their genotype and protein level. Changes in MASP levels were noted in response to chemotherapy and complement function was observed to increase during FN episodes. Structural analysis revealed variability in MBL higher order oligomer structure during the acute phase of FN and promoter studies further highlighted the complexity of MBL regulation. The results presented in this thesis provide further evidence that MBL deficiency increases the frequency and the duration of FN in the largest paediatric cancer cohort studied to date. The complex interplay between other pathway components appears crucial to MBL function but their influence on clinical outcome is not yet fully understood.