The role and diagnosis of complement dysregulation in disease

The proposed research addresses basic questions of how a central part of the immune system is controlled. It is relevant because understanding of these mechanisms and their disturbance in disease will better equip us to identify those at risk of disease to target prevention and treatment.
Complement is part of our immune defence against infection, a group of proteins in blood plasma that recognise, attack and destroy bacteria. This role of complement is important for health and people with complement defects are susceptible to infections. However, this defence comes at a price. Because of its powerful cell-killing properties, complement must be tightly controlled to prevent damage to our own cells resulting in disease. Recently, it has become apparent that small inherited changes in complement proteins, when present in specific combinations, affect this control and greatly increase the risk that complement will attack our own cells and damage organs, particularly kidney and eye. These include a common form of irreversible kidney failure in children (aHUS) and the commonest cause of blindness in the elderly (AMD). We plan to study the ways in which these small inherited changes (either common and called polymorphisms or rare and called mutations) in complement lead to loss of control. To do this we will first gain an understanding of how complement is normally activated and controlled using tools to study the ways that proteins interact. We will use these tools to test how the polymorphisms and mutations weaken control. This knowledge will be used to benefit health in two ways. First, we will develop simple and inexpensive blood tests to identify people carrying risky polymorphisms; those at risk can then be monitored closely to reduce the risk of getting disease. Second, better understanding of the problems in control will enable the design of appropriate treatments to restore control in the complement system to prevent and treat disease.
The work will be performed by a team with proven expertise in complement biology and genetics that has already made contributions to understanding how complement drives disease. The work involves analyses of proteins, either obtained from patients or healthy volunteers or manufactured in the laboratory, to discover how small changes in these proteins predispose to common diseases such as AMD and lethal disorders such as aHUS.

The proposed work will address the hypothesis that subtle effects on activation and regulation caused by common polymorphisms and rare mutations in components and regulators of the complement system synergise to cause dysregulation of complement that predisposes to disease. The hypothesis is built upon accumulating clinical evidence from patients with specific renal and ocular diseases but may have much broader relevance across many pathologies linked by chronic, low-grade inflammation and activation of the alternative pathway of complement. The research objectives are: first, to address how common polymorphisms (individual and in combination) in complement components and regulators affect the assembly, activity and regulation of the convertase enzymes; second, to determine how rare mutations in components and regulators identified in patients affect convertase assembly, activity and regulation; third, to develop tools for the rapid and efficient identification of disease-predisposing combinations of complement polymorphisms in plasma samples from individuals. The work will utilise state-of-the-art methods for analysing the effects of these polymorphisms and mutations on alternative pathway convertase function and regulation. These will include measures of intermolecular interactions using surface plasmon resonance, conformational changes using dual polarisation interferometry, and convertase function using assays of C3 cleavage, convertase decay and haemolytic capacity. These studies will utilise complement proteins and regulators either purified from plasma or recombinantly expressed as appropriate. The results will explain how individual mutations predispose to pathology and identify those combinations of complement polymorphisms that confer high risk of dysregulation and disease. To facilitate identification of individuals with high risk combinations of polymorphisms we will use proven methods to develop novel monoclonal antibodies that distinguish in plasma the relevant polymorphic variants. These will be used to develop simple immunoassays optimised for routine use to enable screening of relevant populations for disease risk. These assays will not only identify the complement polymorphic status of an individual but also quantify the various isoforms of components and regulators in plasma, information that further aids identification of those at risk of disease. The findings will be disseminated through publication and presentation at research and clinical meetings. Commercially exploitable findings will be patented prior to publication. Commercial partners will be involved at an early stage of assay development.